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Rollup merge of #77697 - WaffleLapkin:iter_split_adaptors, r=m-ou-se

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Split each iterator adapter and source into individual modules

This PR creates individual modules for each iterator adapter and iterator source.

This is done to enhance the readability of corresponding modules (`adapters/mod.rs` and `sources.rs`) which were hard to navigate and read because of lots of repeated lines (e.g.: `adapters/mod.rs` was 3k lines long). This is also in line with some adapters which already had their own modules (`Flatten`, `FlatMap`, `Chain`, `Zip`, `Fuse`).

This PR also makes `Take`s adapter fields private (I have no idea why they were `pub(super)` before).

r? ``@LukasKalbertodt``
This commit is contained in:
Mara Bos 2020-11-22 23:00:55 +01:00 committed by GitHub
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33 changed files with 3575 additions and 3467 deletions
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3
library/core/src/iter/adapters/chain.rs
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@ -1,6 +1,5 @@
use crate::iter::{DoubleEndedIterator, FusedIterator, Iterator, TrustedLen};
use crate::ops::Try;
use crate::usize;
use crate::{ops::Try, usize};
/// An iterator that links two iterators together, in a chain.
///

139
library/core/src/iter/adapters/cloned.rs Normal file
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use crate::iter::adapters::{zip::try_get_unchecked, TrustedRandomAccess};
use crate::iter::{FusedIterator, TrustedLen};
use crate::ops::Try;
/// An iterator that clones the elements of an underlying iterator.
///
/// This `struct` is created by the [`cloned`] method on [`Iterator`]. See its
/// documentation for more.
///
/// [`cloned`]: Iterator::cloned
/// [`Iterator`]: trait.Iterator.html
#[stable(feature = "iter_cloned", since = "1.1.0")]
#[must_use = "iterators are lazy and do nothing unless consumed"]
#[derive(Clone, Debug)]
pub struct Cloned<I> {
it: I,
}
impl<I> Cloned<I> {
pub(in crate::iter) fn new(it: I) -> Cloned<I> {
Cloned { it }
}
}
fn clone_try_fold<T: Clone, Acc, R>(mut f: impl FnMut(Acc, T) -> R) -> impl FnMut(Acc, &T) -> R {
move |acc, elt| f(acc, elt.clone())
}
#[stable(feature = "iter_cloned", since = "1.1.0")]
impl<'a, I, T: 'a> Iterator for Cloned<I>
where
I: Iterator<Item = &'a T>,
T: Clone,
{
type Item = T;
fn next(&mut self) -> Option<T> {
self.it.next().cloned()
}
fn size_hint(&self) -> (usize, Option<usize>) {
self.it.size_hint()
}
fn try_fold<B, F, R>(&mut self, init: B, f: F) -> R
where
Self: Sized,
F: FnMut(B, Self::Item) -> R,
R: Try<Ok = B>,
{
self.it.try_fold(init, clone_try_fold(f))
}
fn fold<Acc, F>(self, init: Acc, f: F) -> Acc
where
F: FnMut(Acc, Self::Item) -> Acc,
{
self.it.map(T::clone).fold(init, f)
}
unsafe fn __iterator_get_unchecked(&mut self, idx: usize) -> T
where
Self: TrustedRandomAccess,
{
// SAFETY: the caller must uphold the contract for
// `Iterator::__iterator_get_unchecked`.
unsafe { try_get_unchecked(&mut self.it, idx).clone() }
}
}
#[stable(feature = "iter_cloned", since = "1.1.0")]
impl<'a, I, T: 'a> DoubleEndedIterator for Cloned<I>
where
I: DoubleEndedIterator<Item = &'a T>,
T: Clone,
{
fn next_back(&mut self) -> Option<T> {
self.it.next_back().cloned()
}
fn try_rfold<B, F, R>(&mut self, init: B, f: F) -> R
where
Self: Sized,
F: FnMut(B, Self::Item) -> R,
R: Try<Ok = B>,
{
self.it.try_rfold(init, clone_try_fold(f))
}
fn rfold<Acc, F>(self, init: Acc, f: F) -> Acc
where
F: FnMut(Acc, Self::Item) -> Acc,
{
self.it.map(T::clone).rfold(init, f)
}
}
#[stable(feature = "iter_cloned", since = "1.1.0")]
impl<'a, I, T: 'a> ExactSizeIterator for Cloned<I>
where
I: ExactSizeIterator<Item = &'a T>,
T: Clone,
{
fn len(&self) -> usize {
self.it.len()
}
fn is_empty(&self) -> bool {
self.it.is_empty()
}
}
#[stable(feature = "fused", since = "1.26.0")]
impl<'a, I, T: 'a> FusedIterator for Cloned<I>
where
I: FusedIterator<Item = &'a T>,
T: Clone,
{
}
#[doc(hidden)]
#[unstable(feature = "trusted_random_access", issue = "none")]
unsafe impl<I> TrustedRandomAccess for Cloned<I>
where
I: TrustedRandomAccess,
{
#[inline]
fn may_have_side_effect() -> bool {
true
}
}
#[unstable(feature = "trusted_len", issue = "37572")]
unsafe impl<'a, I, T: 'a> TrustedLen for Cloned<I>
where
I: TrustedLen<Item = &'a T>,
T: Clone,
{
}

155
library/core/src/iter/adapters/copied.rs Normal file
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@ -0,0 +1,155 @@
use crate::iter::adapters::{zip::try_get_unchecked, TrustedRandomAccess};
use crate::iter::{FusedIterator, TrustedLen};
use crate::ops::Try;
/// An iterator that copies the elements of an underlying iterator.
///
/// This `struct` is created by the [`copied`] method on [`Iterator`]. See its
/// documentation for more.
///
/// [`copied`]: Iterator::copied
/// [`Iterator`]: trait.Iterator.html
#[stable(feature = "iter_copied", since = "1.36.0")]
#[must_use = "iterators are lazy and do nothing unless consumed"]
#[derive(Clone, Debug)]
pub struct Copied<I> {
it: I,
}
impl<I> Copied<I> {
pub(in crate::iter) fn new(it: I) -> Copied<I> {
Copied { it }
}
}
fn copy_fold<T: Copy, Acc>(mut f: impl FnMut(Acc, T) -> Acc) -> impl FnMut(Acc, &T) -> Acc {
move |acc, &elt| f(acc, elt)
}
fn copy_try_fold<T: Copy, Acc, R>(mut f: impl FnMut(Acc, T) -> R) -> impl FnMut(Acc, &T) -> R {
move |acc, &elt| f(acc, elt)
}
#[stable(feature = "iter_copied", since = "1.36.0")]
impl<'a, I, T: 'a> Iterator for Copied<I>
where
I: Iterator<Item = &'a T>,
T: Copy,
{
type Item = T;
fn next(&mut self) -> Option<T> {
self.it.next().copied()
}
fn size_hint(&self) -> (usize, Option<usize>) {
self.it.size_hint()
}
fn try_fold<B, F, R>(&mut self, init: B, f: F) -> R
where
Self: Sized,
F: FnMut(B, Self::Item) -> R,
R: Try<Ok = B>,
{
self.it.try_fold(init, copy_try_fold(f))
}
fn fold<Acc, F>(self, init: Acc, f: F) -> Acc
where
F: FnMut(Acc, Self::Item) -> Acc,
{
self.it.fold(init, copy_fold(f))
}
fn nth(&mut self, n: usize) -> Option<T> {
self.it.nth(n).copied()
}
fn last(self) -> Option<T> {
self.it.last().copied()
}
fn count(self) -> usize {
self.it.count()
}
unsafe fn __iterator_get_unchecked(&mut self, idx: usize) -> T
where
Self: TrustedRandomAccess,
{
// SAFETY: the caller must uphold the contract for
// `Iterator::__iterator_get_unchecked`.
*unsafe { try_get_unchecked(&mut self.it, idx) }
}
}
#[stable(feature = "iter_copied", since = "1.36.0")]
impl<'a, I, T: 'a> DoubleEndedIterator for Copied<I>
where
I: DoubleEndedIterator<Item = &'a T>,
T: Copy,
{
fn next_back(&mut self) -> Option<T> {
self.it.next_back().copied()
}
fn try_rfold<B, F, R>(&mut self, init: B, f: F) -> R
where
Self: Sized,
F: FnMut(B, Self::Item) -> R,
R: Try<Ok = B>,
{
self.it.try_rfold(init, copy_try_fold(f))
}
fn rfold<Acc, F>(self, init: Acc, f: F) -> Acc
where
F: FnMut(Acc, Self::Item) -> Acc,
{
self.it.rfold(init, copy_fold(f))
}
}
#[stable(feature = "iter_copied", since = "1.36.0")]
impl<'a, I, T: 'a> ExactSizeIterator for Copied<I>
where
I: ExactSizeIterator<Item = &'a T>,
T: Copy,
{
fn len(&self) -> usize {
self.it.len()
}
fn is_empty(&self) -> bool {
self.it.is_empty()
}
}
#[stable(feature = "iter_copied", since = "1.36.0")]
impl<'a, I, T: 'a> FusedIterator for Copied<I>
where
I: FusedIterator<Item = &'a T>,
T: Copy,
{
}
#[doc(hidden)]
#[unstable(feature = "trusted_random_access", issue = "none")]
unsafe impl<I> TrustedRandomAccess for Copied<I>
where
I: TrustedRandomAccess,
{
#[inline]
fn may_have_side_effect() -> bool {
I::may_have_side_effect()
}
}
#[stable(feature = "iter_copied", since = "1.36.0")]
unsafe impl<'a, I, T: 'a> TrustedLen for Copied<I>
where
I: TrustedLen<Item = &'a T>,
T: Copy,
{
}

87
library/core/src/iter/adapters/cycle.rs Normal file
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@ -0,0 +1,87 @@
use crate::{iter::FusedIterator, ops::Try};
/// An iterator that repeats endlessly.
///
/// This `struct` is created by the [`cycle`] method on [`Iterator`]. See its
/// documentation for more.
///
/// [`cycle`]: Iterator::cycle
/// [`Iterator`]: trait.Iterator.html
#[derive(Clone, Debug)]
#[must_use = "iterators are lazy and do nothing unless consumed"]
#[stable(feature = "rust1", since = "1.0.0")]
pub struct Cycle<I> {
orig: I,
iter: I,
}
impl<I: Clone> Cycle<I> {
pub(in crate::iter) fn new(iter: I) -> Cycle<I> {
Cycle { orig: iter.clone(), iter }
}
}
#[stable(feature = "rust1", since = "1.0.0")]
impl<I> Iterator for Cycle<I>
where
I: Clone + Iterator,
{
type Item = <I as Iterator>::Item;
#[inline]
fn next(&mut self) -> Option<<I as Iterator>::Item> {
match self.iter.next() {
None => {
self.iter = self.orig.clone();
self.iter.next()
}
y => y,
}
}
#[inline]
fn size_hint(&self) -> (usize, Option<usize>) {
// the cycle iterator is either empty or infinite
match self.orig.size_hint() {
sz @ (0, Some(0)) => sz,
(0, _) => (0, None),
_ => (usize::MAX, None),
}
}
#[inline]
fn try_fold<Acc, F, R>(&mut self, mut acc: Acc, mut f: F) -> R
where
F: FnMut(Acc, Self::Item) -> R,
R: Try<Ok = Acc>,
{
// fully iterate the current iterator. this is necessary because
// `self.iter` may be empty even when `self.orig` isn't
acc = self.iter.try_fold(acc, &mut f)?;
self.iter = self.orig.clone();
// complete a full cycle, keeping track of whether the cycled
// iterator is empty or not. we need to return early in case
// of an empty iterator to prevent an infinite loop
let mut is_empty = true;
acc = self.iter.try_fold(acc, |acc, x| {
is_empty = false;
f(acc, x)
})?;
if is_empty {
return try { acc };
}
loop {
self.iter = self.orig.clone();
acc = self.iter.try_fold(acc, &mut f)?;
}
}
// No `fold` override, because `fold` doesn't make much sense for `Cycle`,
// and we can't do anything better than the default.
}
#[stable(feature = "fused", since = "1.26.0")]
impl<I> FusedIterator for Cycle<I> where I: Clone + Iterator {}

238
library/core/src/iter/adapters/enumerate.rs Normal file
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use crate::iter::adapters::{zip::try_get_unchecked, SourceIter, TrustedRandomAccess};
use crate::iter::{FusedIterator, InPlaceIterable, TrustedLen};
use crate::ops::{Add, AddAssign, Try};
/// An iterator that yields the current count and the element during iteration.
///
/// This `struct` is created by the [`enumerate`] method on [`Iterator`]. See its
/// documentation for more.
///
/// [`enumerate`]: Iterator::enumerate
/// [`Iterator`]: trait.Iterator.html
#[derive(Clone, Debug)]
#[must_use = "iterators are lazy and do nothing unless consumed"]
#[stable(feature = "rust1", since = "1.0.0")]
pub struct Enumerate<I> {
iter: I,
count: usize,
}
impl<I> Enumerate<I> {
pub(in crate::iter) fn new(iter: I) -> Enumerate<I> {
Enumerate { iter, count: 0 }
}
}
#[stable(feature = "rust1", since = "1.0.0")]
impl<I> Iterator for Enumerate<I>
where
I: Iterator,
{
type Item = (usize, <I as Iterator>::Item);
/// # Overflow Behavior
///
/// The method does no guarding against overflows, so enumerating more than
/// `usize::MAX` elements either produces the wrong result or panics. If
/// debug assertions are enabled, a panic is guaranteed.
///
/// # Panics
///
/// Might panic if the index of the element overflows a `usize`.
#[inline]
fn next(&mut self) -> Option<(usize, <I as Iterator>::Item)> {
let a = self.iter.next()?;
let i = self.count;
// Possible undefined overflow.
AddAssign::add_assign(&mut self.count, 1);
Some((i, a))
}
#[inline]
fn size_hint(&self) -> (usize, Option<usize>) {
self.iter.size_hint()
}
#[inline]
fn nth(&mut self, n: usize) -> Option<(usize, I::Item)> {
let a = self.iter.nth(n)?;
// Possible undefined overflow.
let i = Add::add(self.count, n);
self.count = Add::add(i, 1);
Some((i, a))
}
#[inline]
fn count(self) -> usize {
self.iter.count()
}
#[inline]
fn try_fold<Acc, Fold, R>(&mut self, init: Acc, fold: Fold) -> R
where
Self: Sized,
Fold: FnMut(Acc, Self::Item) -> R,
R: Try<Ok = Acc>,
{
#[inline]
fn enumerate<'a, T, Acc, R>(
count: &'a mut usize,
mut fold: impl FnMut(Acc, (usize, T)) -> R + 'a,
) -> impl FnMut(Acc, T) -> R + 'a {
move |acc, item| {
let acc = fold(acc, (*count, item));
// Possible undefined overflow.
AddAssign::add_assign(count, 1);
acc
}
}
self.iter.try_fold(init, enumerate(&mut self.count, fold))
}
#[inline]
fn fold<Acc, Fold>(self, init: Acc, fold: Fold) -> Acc
where
Fold: FnMut(Acc, Self::Item) -> Acc,
{
#[inline]
fn enumerate<T, Acc>(
mut count: usize,
mut fold: impl FnMut(Acc, (usize, T)) -> Acc,
) -> impl FnMut(Acc, T) -> Acc {
move |acc, item| {
let acc = fold(acc, (count, item));
// Possible undefined overflow.
AddAssign::add_assign(&mut count, 1);
acc
}
}
self.iter.fold(init, enumerate(self.count, fold))
}
unsafe fn __iterator_get_unchecked(&mut self, idx: usize) -> <Self as Iterator>::Item
where
Self: TrustedRandomAccess,
{
// SAFETY: the caller must uphold the contract for
// `Iterator::__iterator_get_unchecked`.
let value = unsafe { try_get_unchecked(&mut self.iter, idx) };
(Add::add(self.count, idx), value)
}
}
#[stable(feature = "rust1", since = "1.0.0")]
impl<I> DoubleEndedIterator for Enumerate<I>
where
I: ExactSizeIterator + DoubleEndedIterator,
{
#[inline]
fn next_back(&mut self) -> Option<(usize, <I as Iterator>::Item)> {
let a = self.iter.next_back()?;
let len = self.iter.len();
// Can safely add, `ExactSizeIterator` promises that the number of
// elements fits into a `usize`.
Some((self.count + len, a))
}
#[inline]
fn nth_back(&mut self, n: usize) -> Option<(usize, <I as Iterator>::Item)> {
let a = self.iter.nth_back(n)?;
let len = self.iter.len();
// Can safely add, `ExactSizeIterator` promises that the number of
// elements fits into a `usize`.
Some((self.count + len, a))
}
#[inline]
fn try_rfold<Acc, Fold, R>(&mut self, init: Acc, fold: Fold) -> R
where
Self: Sized,
Fold: FnMut(Acc, Self::Item) -> R,
R: Try<Ok = Acc>,
{
// Can safely add and subtract the count, as `ExactSizeIterator` promises
// that the number of elements fits into a `usize`.
fn enumerate<T, Acc, R>(
mut count: usize,
mut fold: impl FnMut(Acc, (usize, T)) -> R,
) -> impl FnMut(Acc, T) -> R {
move |acc, item| {
count -= 1;
fold(acc, (count, item))
}
}
let count = self.count + self.iter.len();
self.iter.try_rfold(init, enumerate(count, fold))
}
#[inline]
fn rfold<Acc, Fold>(self, init: Acc, fold: Fold) -> Acc
where
Fold: FnMut(Acc, Self::Item) -> Acc,
{
// Can safely add and subtract the count, as `ExactSizeIterator` promises
// that the number of elements fits into a `usize`.
fn enumerate<T, Acc>(
mut count: usize,
mut fold: impl FnMut(Acc, (usize, T)) -> Acc,
) -> impl FnMut(Acc, T) -> Acc {
move |acc, item| {
count -= 1;
fold(acc, (count, item))
}
}
let count = self.count + self.iter.len();
self.iter.rfold(init, enumerate(count, fold))
}
}
#[stable(feature = "rust1", since = "1.0.0")]
impl<I> ExactSizeIterator for Enumerate<I>
where
I: ExactSizeIterator,
{
fn len(&self) -> usize {
self.iter.len()
}
fn is_empty(&self) -> bool {
self.iter.is_empty()
}
}
#[doc(hidden)]
#[unstable(feature = "trusted_random_access", issue = "none")]
unsafe impl<I> TrustedRandomAccess for Enumerate<I>
where
I: TrustedRandomAccess,
{
fn may_have_side_effect() -> bool {
I::may_have_side_effect()
}
}
#[stable(feature = "fused", since = "1.26.0")]
impl<I> FusedIterator for Enumerate<I> where I: FusedIterator {}
#[unstable(feature = "trusted_len", issue = "37572")]
unsafe impl<I> TrustedLen for Enumerate<I> where I: TrustedLen {}
#[unstable(issue = "none", feature = "inplace_iteration")]
unsafe impl<S: Iterator, I: Iterator> SourceIter for Enumerate<I>
where
I: SourceIter<Source = S>,
{
type Source = S;
#[inline]
unsafe fn as_inner(&mut self) -> &mut S {
// SAFETY: unsafe function forwarding to unsafe function with the same requirements
unsafe { SourceIter::as_inner(&mut self.iter) }
}
}
#[unstable(issue = "none", feature = "inplace_iteration")]
unsafe impl<I: InPlaceIterable> InPlaceIterable for Enumerate<I> {}

152
library/core/src/iter/adapters/filter.rs Normal file
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use crate::fmt;
use crate::iter::{adapters::SourceIter, FusedIterator, InPlaceIterable};
use crate::ops::Try;
/// An iterator that filters the elements of `iter` with `predicate`.
///
/// This `struct` is created by the [`filter`] method on [`Iterator`]. See its
/// documentation for more.
///
/// [`filter`]: Iterator::filter
/// [`Iterator`]: trait.Iterator.html
#[must_use = "iterators are lazy and do nothing unless consumed"]
#[stable(feature = "rust1", since = "1.0.0")]
#[derive(Clone)]
pub struct Filter<I, P> {
iter: I,
predicate: P,
}
impl<I, P> Filter<I, P> {
pub(in crate::iter) fn new(iter: I, predicate: P) -> Filter<I, P> {
Filter { iter, predicate }
}
}
#[stable(feature = "core_impl_debug", since = "1.9.0")]
impl<I: fmt::Debug, P> fmt::Debug for Filter<I, P> {
fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
f.debug_struct("Filter").field("iter", &self.iter).finish()
}
}
fn filter_fold<T, Acc>(
mut predicate: impl FnMut(&T) -> bool,
mut fold: impl FnMut(Acc, T) -> Acc,
) -> impl FnMut(Acc, T) -> Acc {
move |acc, item| if predicate(&item) { fold(acc, item) } else { acc }
}
fn filter_try_fold<'a, T, Acc, R: Try<Ok = Acc>>(
predicate: &'a mut impl FnMut(&T) -> bool,
mut fold: impl FnMut(Acc, T) -> R + 'a,
) -> impl FnMut(Acc, T) -> R + 'a {
move |acc, item| if predicate(&item) { fold(acc, item) } else { try { acc } }
}
#[stable(feature = "rust1", since = "1.0.0")]
impl<I: Iterator, P> Iterator for Filter<I, P>
where
P: FnMut(&I::Item) -> bool,
{
type Item = I::Item;
#[inline]
fn next(&mut self) -> Option<I::Item> {
self.iter.find(&mut self.predicate)
}
#[inline]
fn size_hint(&self) -> (usize, Option<usize>) {
let (_, upper) = self.iter.size_hint();
(0, upper) // can't know a lower bound, due to the predicate
}
// this special case allows the compiler to make `.filter(_).count()`
// branchless. Barring perfect branch prediction (which is unattainable in
// the general case), this will be much faster in >90% of cases (containing
// virtually all real workloads) and only a tiny bit slower in the rest.
//
// Having this specialization thus allows us to write `.filter(p).count()`
// where we would otherwise write `.map(|x| p(x) as usize).sum()`, which is
// less readable and also less backwards-compatible to Rust before 1.10.
//
// Using the branchless version will also simplify the LLVM byte code, thus
// leaving more budget for LLVM optimizations.
#[inline]
fn count(self) -> usize {
#[inline]
fn to_usize<T>(mut predicate: impl FnMut(&T) -> bool) -> impl FnMut(T) -> usize {
move |x| predicate(&x) as usize
}
self.iter.map(to_usize(self.predicate)).sum()
}
#[inline]
fn try_fold<Acc, Fold, R>(&mut self, init: Acc, fold: Fold) -> R
where
Self: Sized,
Fold: FnMut(Acc, Self::Item) -> R,
R: Try<Ok = Acc>,
{
self.iter.try_fold(init, filter_try_fold(&mut self.predicate, fold))
}
#[inline]
fn fold<Acc, Fold>(self, init: Acc, fold: Fold) -> Acc
where
Fold: FnMut(Acc, Self::Item) -> Acc,
{
self.iter.fold(init, filter_fold(self.predicate, fold))
}
}
#[stable(feature = "rust1", since = "1.0.0")]
impl<I: DoubleEndedIterator, P> DoubleEndedIterator for Filter<I, P>
where
P: FnMut(&I::Item) -> bool,
{
#[inline]
fn next_back(&mut self) -> Option<I::Item> {
self.iter.rfind(&mut self.predicate)
}
#[inline]
fn try_rfold<Acc, Fold, R>(&mut self, init: Acc, fold: Fold) -> R
where
Self: Sized,
Fold: FnMut(Acc, Self::Item) -> R,
R: Try<Ok = Acc>,
{
self.iter.try_rfold(init, filter_try_fold(&mut self.predicate, fold))
}
#[inline]
fn rfold<Acc, Fold>(self, init: Acc, fold: Fold) -> Acc
where
Fold: FnMut(Acc, Self::Item) -> Acc,
{
self.iter.rfold(init, filter_fold(self.predicate, fold))
}
}
#[stable(feature = "fused", since = "1.26.0")]
impl<I: FusedIterator, P> FusedIterator for Filter<I, P> where P: FnMut(&I::Item) -> bool {}
#[unstable(issue = "none", feature = "inplace_iteration")]
unsafe impl<S: Iterator, P, I: Iterator> SourceIter for Filter<I, P>
where
P: FnMut(&I::Item) -> bool,
I: SourceIter<Source = S>,
{
type Source = S;
#[inline]
unsafe fn as_inner(&mut self) -> &mut S {
// SAFETY: unsafe function forwarding to unsafe function with the same requirements
unsafe { SourceIter::as_inner(&mut self.iter) }
}
}
#[unstable(issue = "none", feature = "inplace_iteration")]
unsafe impl<I: InPlaceIterable, P> InPlaceIterable for Filter<I, P> where P: FnMut(&I::Item) -> bool {}

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@ -0,0 +1,150 @@
use crate::fmt;
use crate::iter::{adapters::SourceIter, FusedIterator, InPlaceIterable};
use crate::ops::{ControlFlow, Try};
/// An iterator that uses `f` to both filter and map elements from `iter`.
///
/// This `struct` is created by the [`filter_map`] method on [`Iterator`]. See its
/// documentation for more.
///
/// [`filter_map`]: Iterator::filter_map
/// [`Iterator`]: trait.Iterator.html
#[must_use = "iterators are lazy and do nothing unless consumed"]
#[stable(feature = "rust1", since = "1.0.0")]
#[derive(Clone)]
pub struct FilterMap<I, F> {
iter: I,
f: F,
}
impl<I, F> FilterMap<I, F> {
pub(in crate::iter) fn new(iter: I, f: F) -> FilterMap<I, F> {
FilterMap { iter, f }
}
}
#[stable(feature = "core_impl_debug", since = "1.9.0")]
impl<I: fmt::Debug, F> fmt::Debug for FilterMap<I, F> {
fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
f.debug_struct("FilterMap").field("iter", &self.iter).finish()
}
}
fn filter_map_fold<T, B, Acc>(
mut f: impl FnMut(T) -> Option<B>,
mut fold: impl FnMut(Acc, B) -> Acc,
) -> impl FnMut(Acc, T) -> Acc {
move |acc, item| match f(item) {
Some(x) => fold(acc, x),
None => acc,
}
}
fn filter_map_try_fold<'a, T, B, Acc, R: Try<Ok = Acc>>(
f: &'a mut impl FnMut(T) -> Option<B>,
mut fold: impl FnMut(Acc, B) -> R + 'a,
) -> impl FnMut(Acc, T) -> R + 'a {
move |acc, item| match f(item) {
Some(x) => fold(acc, x),
None => try { acc },
}
}
#[stable(feature = "rust1", since = "1.0.0")]
impl<B, I: Iterator, F> Iterator for FilterMap<I, F>
where
F: FnMut(I::Item) -> Option<B>,
{
type Item = B;
#[inline]
fn next(&mut self) -> Option<B> {
self.iter.find_map(&mut self.f)
}
#[inline]
fn size_hint(&self) -> (usize, Option<usize>) {
let (_, upper) = self.iter.size_hint();
(0, upper) // can't know a lower bound, due to the predicate
}
#[inline]
fn try_fold<Acc, Fold, R>(&mut self, init: Acc, fold: Fold) -> R
where
Self: Sized,
Fold: FnMut(Acc, Self::Item) -> R,
R: Try<Ok = Acc>,
{
self.iter.try_fold(init, filter_map_try_fold(&mut self.f, fold))
}
#[inline]
fn fold<Acc, Fold>(self, init: Acc, fold: Fold) -> Acc
where
Fold: FnMut(Acc, Self::Item) -> Acc,
{
self.iter.fold(init, filter_map_fold(self.f, fold))
}
}
#[stable(feature = "rust1", since = "1.0.0")]
impl<B, I: DoubleEndedIterator, F> DoubleEndedIterator for FilterMap<I, F>
where
F: FnMut(I::Item) -> Option<B>,
{
#[inline]
fn next_back(&mut self) -> Option<B> {
#[inline]
fn find<T, B>(
f: &mut impl FnMut(T) -> Option<B>,
) -> impl FnMut((), T) -> ControlFlow<B> + '_ {
move |(), x| match f(x) {
Some(x) => ControlFlow::Break(x),
None => ControlFlow::CONTINUE,
}
}
self.iter.try_rfold((), find(&mut self.f)).break_value()
}
#[inline]
fn try_rfold<Acc, Fold, R>(&mut self, init: Acc, fold: Fold) -> R
where
Self: Sized,
Fold: FnMut(Acc, Self::Item) -> R,
R: Try<Ok = Acc>,
{
self.iter.try_rfold(init, filter_map_try_fold(&mut self.f, fold))
}
#[inline]
fn rfold<Acc, Fold>(self, init: Acc, fold: Fold) -> Acc
where
Fold: FnMut(Acc, Self::Item) -> Acc,
{
self.iter.rfold(init, filter_map_fold(self.f, fold))
}
}
#[stable(feature = "fused", since = "1.26.0")]
impl<B, I: FusedIterator, F> FusedIterator for FilterMap<I, F> where F: FnMut(I::Item) -> Option<B> {}
#[unstable(issue = "none", feature = "inplace_iteration")]
unsafe impl<S: Iterator, B, I: Iterator, F> SourceIter for FilterMap<I, F>
where
F: FnMut(I::Item) -> Option<B>,
I: SourceIter<Source = S>,
{
type Source = S;
#[inline]
unsafe fn as_inner(&mut self) -> &mut S {
// SAFETY: unsafe function forwarding to unsafe function with the same requirements
unsafe { SourceIter::as_inner(&mut self.iter) }
}
}
#[unstable(issue = "none", feature = "inplace_iteration")]
unsafe impl<B, I: InPlaceIterable, F> InPlaceIterable for FilterMap<I, F> where
F: FnMut(I::Item) -> Option<B>
{
}

7
library/core/src/iter/adapters/flatten.rs
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@ -1,9 +1,7 @@
use crate::fmt;
use crate::iter::{DoubleEndedIterator, Fuse, FusedIterator, Iterator, Map};
use crate::ops::Try;
use super::super::{DoubleEndedIterator, Fuse, FusedIterator, Iterator};
use super::Map;
/// An iterator that maps each element to an iterator, and yields the elements
/// of the produced iterators.
///
@ -14,8 +12,9 @@ use super::Map;
pub struct FlatMap<I, U: IntoIterator, F> {
inner: FlattenCompat<Map<I, F>, <U as IntoIterator>::IntoIter>,
}
impl<I: Iterator, U: IntoIterator, F: FnMut(I::Item) -> U> FlatMap<I, U, F> {
pub(in super::super) fn new(iter: I, f: F) -> FlatMap<I, U, F> {
pub(in crate::iter) fn new(iter: I, f: F) -> FlatMap<I, U, F> {
FlatMap { inner: FlattenCompat::new(iter.map(f)) }
}
}

7
library/core/src/iter/adapters/fuse.rs
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@ -1,9 +1,6 @@
use super::InPlaceIterable;
use crate::intrinsics;
use crate::iter::adapters::zip::try_get_unchecked;
use crate::iter::adapters::SourceIter;
use crate::iter::TrustedRandomAccess;
use crate::iter::{DoubleEndedIterator, ExactSizeIterator, FusedIterator, Iterator};
use crate::iter::adapters::{zip::try_get_unchecked, InPlaceIterable, SourceIter};
use crate::iter::{DoubleEndedIterator, ExactSizeIterator, FusedIterator, TrustedRandomAccess};
use crate::ops::Try;
/// An iterator that yields `None` forever after the underlying iterator

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use crate::fmt;
use crate::iter::{adapters::SourceIter, FusedIterator, InPlaceIterable};
use crate::ops::Try;
/// An iterator that calls a function with a reference to each element before
/// yielding it.
///
/// This `struct` is created by the [`inspect`] method on [`Iterator`]. See its
/// documentation for more.
///
/// [`inspect`]: Iterator::inspect
/// [`Iterator`]: trait.Iterator.html
#[must_use = "iterators are lazy and do nothing unless consumed"]
#[stable(feature = "rust1", since = "1.0.0")]
#[derive(Clone)]
pub struct Inspect<I, F> {
iter: I,
f: F,
}
impl<I, F> Inspect<I, F> {
pub(in crate::iter) fn new(iter: I, f: F) -> Inspect<I, F> {
Inspect { iter, f }
}
}
#[stable(feature = "core_impl_debug", since = "1.9.0")]
impl<I: fmt::Debug, F> fmt::Debug for Inspect<I, F> {
fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
f.debug_struct("Inspect").field("iter", &self.iter).finish()
}
}
impl<I: Iterator, F> Inspect<I, F>
where
F: FnMut(&I::Item),
{
#[inline]
fn do_inspect(&mut self, elt: Option<I::Item>) -> Option<I::Item> {
if let Some(ref a) = elt {
(self.f)(a);
}
elt
}
}
fn inspect_fold<T, Acc>(
mut f: impl FnMut(&T),
mut fold: impl FnMut(Acc, T) -> Acc,
) -> impl FnMut(Acc, T) -> Acc {
move |acc, item| {
f(&item);
fold(acc, item)
}
}
fn inspect_try_fold<'a, T, Acc, R>(
f: &'a mut impl FnMut(&T),
mut fold: impl FnMut(Acc, T) -> R + 'a,
) -> impl FnMut(Acc, T) -> R + 'a {
move |acc, item| {
f(&item);
fold(acc, item)
}
}
#[stable(feature = "rust1", since = "1.0.0")]
impl<I: Iterator, F> Iterator for Inspect<I, F>
where
F: FnMut(&I::Item),
{
type Item = I::Item;
#[inline]
fn next(&mut self) -> Option<I::Item> {
let next = self.iter.next();
self.do_inspect(next)
}
#[inline]
fn size_hint(&self) -> (usize, Option<usize>) {
self.iter.size_hint()
}
#[inline]
fn try_fold<Acc, Fold, R>(&mut self, init: Acc, fold: Fold) -> R
where
Self: Sized,
Fold: FnMut(Acc, Self::Item) -> R,
R: Try<Ok = Acc>,
{
self.iter.try_fold(init, inspect_try_fold(&mut self.f, fold))
}
#[inline]
fn fold<Acc, Fold>(self, init: Acc, fold: Fold) -> Acc
where
Fold: FnMut(Acc, Self::Item) -> Acc,
{
self.iter.fold(init, inspect_fold(self.f, fold))
}
}
#[stable(feature = "rust1", since = "1.0.0")]
impl<I: DoubleEndedIterator, F> DoubleEndedIterator for Inspect<I, F>
where
F: FnMut(&I::Item),
{
#[inline]
fn next_back(&mut self) -> Option<I::Item> {
let next = self.iter.next_back();
self.do_inspect(next)
}
#[inline]
fn try_rfold<Acc, Fold, R>(&mut self, init: Acc, fold: Fold) -> R
where
Self: Sized,
Fold: FnMut(Acc, Self::Item) -> R,
R: Try<Ok = Acc>,
{
self.iter.try_rfold(init, inspect_try_fold(&mut self.f, fold))
}
#[inline]
fn rfold<Acc, Fold>(self, init: Acc, fold: Fold) -> Acc
where
Fold: FnMut(Acc, Self::Item) -> Acc,
{
self.iter.rfold(init, inspect_fold(self.f, fold))
}
}
#[stable(feature = "rust1", since = "1.0.0")]
impl<I: ExactSizeIterator, F> ExactSizeIterator for Inspect<I, F>
where
F: FnMut(&I::Item),
{
fn len(&self) -> usize {
self.iter.len()
}
fn is_empty(&self) -> bool {
self.iter.is_empty()
}
}
#[stable(feature = "fused", since = "1.26.0")]
impl<I: FusedIterator, F> FusedIterator for Inspect<I, F> where F: FnMut(&I::Item) {}
#[unstable(issue = "none", feature = "inplace_iteration")]
unsafe impl<S: Iterator, I: Iterator, F> SourceIter for Inspect<I, F>
where
F: FnMut(&I::Item),
I: SourceIter<Source = S>,
{
type Source = S;
#[inline]
unsafe fn as_inner(&mut self) -> &mut S {
// SAFETY: unsafe function forwarding to unsafe function with the same requirements
unsafe { SourceIter::as_inner(&mut self.iter) }
}
}
#[unstable(issue = "none", feature = "inplace_iteration")]
unsafe impl<I: InPlaceIterable, F> InPlaceIterable for Inspect<I, F> where F: FnMut(&I::Item) {}

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use crate::fmt;
use crate::iter::adapters::{zip::try_get_unchecked, SourceIter, TrustedRandomAccess};
use crate::iter::{FusedIterator, InPlaceIterable, TrustedLen};
use crate::ops::Try;
/// An iterator that maps the values of `iter` with `f`.
///
/// This `struct` is created by the [`map`] method on [`Iterator`]. See its
/// documentation for more.
///
/// [`map`]: Iterator::map
/// [`Iterator`]: trait.Iterator.html
///
/// # Notes about side effects
///
/// The [`map`] iterator implements [`DoubleEndedIterator`], meaning that
/// you can also [`map`] backwards:
///
/// ```rust
/// let v: Vec<i32> = vec![1, 2, 3].into_iter().map(|x| x + 1).rev().collect();
///
/// assert_eq!(v, [4, 3, 2]);
/// ```
///
/// [`DoubleEndedIterator`]: trait.DoubleEndedIterator.html
///
/// But if your closure has state, iterating backwards may act in a way you do
/// not expect. Let's go through an example. First, in the forward direction:
///
/// ```rust
/// let mut c = 0;
///
/// for pair in vec!['a', 'b', 'c'].into_iter()
/// .map(|letter| { c += 1; (letter, c) }) {
/// println!("{:?}", pair);
/// }
/// ```
///
/// This will print "('a', 1), ('b', 2), ('c', 3)".
///
/// Now consider this twist where we add a call to `rev`. This version will
/// print `('c', 1), ('b', 2), ('a', 3)`. Note that the letters are reversed,
/// but the values of the counter still go in order. This is because `map()` is
/// still being called lazily on each item, but we are popping items off the
/// back of the vector now, instead of shifting them from the front.
///
/// ```rust
/// let mut c = 0;
///
/// for pair in vec!['a', 'b', 'c'].into_iter()
/// .map(|letter| { c += 1; (letter, c) })
/// .rev() {
/// println!("{:?}", pair);
/// }
/// ```
#[must_use = "iterators are lazy and do nothing unless consumed"]
#[stable(feature = "rust1", since = "1.0.0")]
#[derive(Clone)]
pub struct Map<I, F> {
iter: I,
f: F,
}
impl<I, F> Map<I, F> {
pub(in crate::iter) fn new(iter: I, f: F) -> Map<I, F> {
Map { iter, f }
}
}
#[stable(feature = "core_impl_debug", since = "1.9.0")]
impl<I: fmt::Debug, F> fmt::Debug for Map<I, F> {
fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
f.debug_struct("Map").field("iter", &self.iter).finish()
}
}
fn map_fold<T, B, Acc>(
mut f: impl FnMut(T) -> B,
mut g: impl FnMut(Acc, B) -> Acc,
) -> impl FnMut(Acc, T) -> Acc {
move |acc, elt| g(acc, f(elt))
}
fn map_try_fold<'a, T, B, Acc, R>(
f: &'a mut impl FnMut(T) -> B,
mut g: impl FnMut(Acc, B) -> R + 'a,
) -> impl FnMut(Acc, T) -> R + 'a {
move |acc, elt| g(acc, f(elt))
}
#[stable(feature = "rust1", since = "1.0.0")]
impl<B, I: Iterator, F> Iterator for Map<I, F>
where
F: FnMut(I::Item) -> B,
{
type Item = B;
#[inline]
fn next(&mut self) -> Option<B> {
self.iter.next().map(&mut self.f)
}
#[inline]
fn size_hint(&self) -> (usize, Option<usize>) {
self.iter.size_hint()
}
fn try_fold<Acc, G, R>(&mut self, init: Acc, g: G) -> R
where
Self: Sized,
G: FnMut(Acc, Self::Item) -> R,
R: Try<Ok = Acc>,
{
self.iter.try_fold(init, map_try_fold(&mut self.f, g))
}
fn fold<Acc, G>(self, init: Acc, g: G) -> Acc
where
G: FnMut(Acc, Self::Item) -> Acc,
{
self.iter.fold(init, map_fold(self.f, g))
}
unsafe fn __iterator_get_unchecked(&mut self, idx: usize) -> B
where
Self: TrustedRandomAccess,
{
// SAFETY: the caller must uphold the contract for
// `Iterator::__iterator_get_unchecked`.
unsafe { (self.f)(try_get_unchecked(&mut self.iter, idx)) }
}
}
#[stable(feature = "rust1", since = "1.0.0")]
impl<B, I: DoubleEndedIterator, F> DoubleEndedIterator for Map<I, F>
where
F: FnMut(I::Item) -> B,
{
#[inline]
fn next_back(&mut self) -> Option<B> {
self.iter.next_back().map(&mut self.f)
}
fn try_rfold<Acc, G, R>(&mut self, init: Acc, g: G) -> R
where
Self: Sized,
G: FnMut(Acc, Self::Item) -> R,
R: Try<Ok = Acc>,
{
self.iter.try_rfold(init, map_try_fold(&mut self.f, g))
}
fn rfold<Acc, G>(self, init: Acc, g: G) -> Acc
where
G: FnMut(Acc, Self::Item) -> Acc,
{
self.iter.rfold(init, map_fold(self.f, g))
}
}
#[stable(feature = "rust1", since = "1.0.0")]
impl<B, I: ExactSizeIterator, F> ExactSizeIterator for Map<I, F>
where
F: FnMut(I::Item) -> B,
{
fn len(&self) -> usize {
self.iter.len()
}
fn is_empty(&self) -> bool {
self.iter.is_empty()
}
}
#[stable(feature = "fused", since = "1.26.0")]
impl<B, I: FusedIterator, F> FusedIterator for Map<I, F> where F: FnMut(I::Item) -> B {}
#[unstable(feature = "trusted_len", issue = "37572")]
unsafe impl<B, I, F> TrustedLen for Map<I, F>
where
I: TrustedLen,
F: FnMut(I::Item) -> B,
{
}
#[doc(hidden)]
#[unstable(feature = "trusted_random_access", issue = "none")]
unsafe impl<I, F> TrustedRandomAccess for Map<I, F>
where
I: TrustedRandomAccess,
{
#[inline]
fn may_have_side_effect() -> bool {
true
}
}
#[unstable(issue = "none", feature = "inplace_iteration")]
unsafe impl<S: Iterator, B, I: Iterator, F> SourceIter for Map<I, F>
where
F: FnMut(I::Item) -> B,
I: SourceIter<Source = S>,
{
type Source = S;
#[inline]
unsafe fn as_inner(&mut self) -> &mut S {
// SAFETY: unsafe function forwarding to unsafe function with the same requirements
unsafe { SourceIter::as_inner(&mut self.iter) }
}
}
#[unstable(issue = "none", feature = "inplace_iteration")]
unsafe impl<B, I: InPlaceIterable, F> InPlaceIterable for Map<I, F> where F: FnMut(I::Item) -> B {}

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use crate::fmt;
use crate::iter::{adapters::SourceIter, InPlaceIterable};
use crate::ops::{ControlFlow, Try};
/// An iterator that only accepts elements while `predicate` returns `Some(_)`.
///
/// This `struct` is created by the [`map_while`] method on [`Iterator`]. See its
/// documentation for more.
///
/// [`map_while`]: Iterator::map_while
/// [`Iterator`]: trait.Iterator.html
#[must_use = "iterators are lazy and do nothing unless consumed"]
#[unstable(feature = "iter_map_while", reason = "recently added", issue = "68537")]
#[derive(Clone)]
pub struct MapWhile<I, P> {
iter: I,
predicate: P,
}
impl<I, P> MapWhile<I, P> {
pub(in crate::iter) fn new(iter: I, predicate: P) -> MapWhile<I, P> {
MapWhile { iter, predicate }
}
}
#[unstable(feature = "iter_map_while", reason = "recently added", issue = "68537")]
impl<I: fmt::Debug, P> fmt::Debug for MapWhile<I, P> {
fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
f.debug_struct("MapWhile").field("iter", &self.iter).finish()
}
}
#[unstable(feature = "iter_map_while", reason = "recently added", issue = "68537")]
impl<B, I: Iterator, P> Iterator for MapWhile<I, P>
where
P: FnMut(I::Item) -> Option<B>,
{
type Item = B;
#[inline]
fn next(&mut self) -> Option<B> {
let x = self.iter.next()?;
(self.predicate)(x)
}
#[inline]
fn size_hint(&self) -> (usize, Option<usize>) {
let (_, upper) = self.iter.size_hint();
(0, upper) // can't know a lower bound, due to the predicate
}
#[inline]
fn try_fold<Acc, Fold, R>(&mut self, init: Acc, mut fold: Fold) -> R
where
Self: Sized,
Fold: FnMut(Acc, Self::Item) -> R,
R: Try<Ok = Acc>,
{
let Self { iter, predicate } = self;
iter.try_fold(init, |acc, x| match predicate(x) {
Some(item) => ControlFlow::from_try(fold(acc, item)),
None => ControlFlow::Break(try { acc }),
})
.into_try()
}
#[inline]
fn fold<Acc, Fold>(mut self, init: Acc, fold: Fold) -> Acc
where
Self: Sized,
Fold: FnMut(Acc, Self::Item) -> Acc,
{
#[inline]
fn ok<B, T>(mut f: impl FnMut(B, T) -> B) -> impl FnMut(B, T) -> Result<B, !> {
move |acc, x| Ok(f(acc, x))
}
self.try_fold(init, ok(fold)).unwrap()
}
}
#[unstable(issue = "none", feature = "inplace_iteration")]
unsafe impl<S: Iterator, B, I: Iterator, P> SourceIter for MapWhile<I, P>
where
P: FnMut(I::Item) -> Option<B>,
I: SourceIter<Source = S>,
{
type Source = S;
#[inline]
unsafe fn as_inner(&mut self) -> &mut S {
// SAFETY: unsafe function forwarding to unsafe function with the same requirements
unsafe { SourceIter::as_inner(&mut self.iter) }
}
}
#[unstable(issue = "none", feature = "inplace_iteration")]
unsafe impl<B, I: InPlaceIterable, P> InPlaceIterable for MapWhile<I, P> where
P: FnMut(I::Item) -> Option<B>
{
}

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library/core/src/iter/adapters/peekable.rs Normal file
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use crate::iter::{adapters::SourceIter, FusedIterator, InPlaceIterable, TrustedLen};
use crate::ops::Try;
/// An iterator with a `peek()` that returns an optional reference to the next
/// element.
///
/// This `struct` is created by the [`peekable`] method on [`Iterator`]. See its
/// documentation for more.
///
/// [`peekable`]: Iterator::peekable
/// [`Iterator`]: trait.Iterator.html
#[derive(Clone, Debug)]
#[must_use = "iterators are lazy and do nothing unless consumed"]
#[stable(feature = "rust1", since = "1.0.0")]
pub struct Peekable<I: Iterator> {
iter: I,
/// Remember a peeked value, even if it was None.
peeked: Option<Option<I::Item>>,
}
impl<I: Iterator> Peekable<I> {
pub(in crate::iter) fn new(iter: I) -> Peekable<I> {
Peekable { iter, peeked: None }
}
}
// Peekable must remember if a None has been seen in the `.peek()` method.
// It ensures that `.peek(); .peek();` or `.peek(); .next();` only advances the
// underlying iterator at most once. This does not by itself make the iterator
// fused.
#[stable(feature = "rust1", since = "1.0.0")]
impl<I: Iterator> Iterator for Peekable<I> {
type Item = I::Item;
#[inline]
fn next(&mut self) -> Option<I::Item> {
match self.peeked.take() {
Some(v) => v,
None => self.iter.next(),
}
}
#[inline]
#[rustc_inherit_overflow_checks]
fn count(mut self) -> usize {
match self.peeked.take() {
Some(None) => 0,
Some(Some(_)) => 1 + self.iter.count(),
None => self.iter.count(),
}
}
#[inline]
fn nth(&mut self, n: usize) -> Option<I::Item> {
match self.peeked.take() {
Some(None) => None,
Some(v @ Some(_)) if n == 0 => v,
Some(Some(_)) => self.iter.nth(n - 1),
None => self.iter.nth(n),
}
}
#[inline]
fn last(mut self) -> Option<I::Item> {
let peek_opt = match self.peeked.take() {
Some(None) => return None,
Some(v) => v,
None => None,
};
self.iter.last().or(peek_opt)
}
#[inline]
fn size_hint(&self) -> (usize, Option<usize>) {
let peek_len = match self.peeked {
Some(None) => return (0, Some(0)),
Some(Some(_)) => 1,
None => 0,
};
let (lo, hi) = self.iter.size_hint();
let lo = lo.saturating_add(peek_len);
let hi = match hi {
Some(x) => x.checked_add(peek_len),
None => None,
};
(lo, hi)
}
#[inline]
fn try_fold<B, F, R>(&mut self, init: B, mut f: F) -> R
where
Self: Sized,
F: FnMut(B, Self::Item) -> R,
R: Try<Ok = B>,
{
let acc = match self.peeked.take() {
Some(None) => return try { init },
Some(Some(v)) => f(init, v)?,
None => init,
};
self.iter.try_fold(acc, f)
}
#[inline]
fn fold<Acc, Fold>(self, init: Acc, mut fold: Fold) -> Acc
where
Fold: FnMut(Acc, Self::Item) -> Acc,
{
let acc = match self.peeked {
Some(None) => return init,
Some(Some(v)) => fold(init, v),
None => init,
};
self.iter.fold(acc, fold)
}
}
#[stable(feature = "double_ended_peek_iterator", since = "1.38.0")]
impl<I> DoubleEndedIterator for Peekable<I>
where
I: DoubleEndedIterator,
{
#[inline]
fn next_back(&mut self) -> Option<Self::Item> {
match self.peeked.as_mut() {
Some(v @ Some(_)) => self.iter.next_back().or_else(|| v.take()),
Some(None) => None,
None => self.iter.next_back(),
}
}
#[inline]
fn try_rfold<B, F, R>(&mut self, init: B, mut f: F) -> R
where
Self: Sized,
F: FnMut(B, Self::Item) -> R,
R: Try<Ok = B>,
{
match self.peeked.take() {
Some(None) => try { init },
Some(Some(v)) => match self.iter.try_rfold(init, &mut f).into_result() {
Ok(acc) => f(acc, v),
Err(e) => {
self.peeked = Some(Some(v));
Try::from_error(e)
}
},
None => self.iter.try_rfold(init, f),
}
}
#[inline]
fn rfold<Acc, Fold>(self, init: Acc, mut fold: Fold) -> Acc
where
Fold: FnMut(Acc, Self::Item) -> Acc,
{
match self.peeked {
Some(None) => init,
Some(Some(v)) => {
let acc = self.iter.rfold(init, &mut fold);
fold(acc, v)
}
None => self.iter.rfold(init, fold),
}
}
}
#[stable(feature = "rust1", since = "1.0.0")]
impl<I: ExactSizeIterator> ExactSizeIterator for Peekable<I> {}
#[stable(feature = "fused", since = "1.26.0")]
impl<I: FusedIterator> FusedIterator for Peekable<I> {}
impl<I: Iterator> Peekable<I> {
/// Returns a reference to the next() value without advancing the iterator.
///
/// Like [`next`], if there is a value, it is wrapped in a `Some(T)`.
/// But if the iteration is over, `None` is returned.
///
/// [`next`]: Iterator::next
///
/// Because `peek()` returns a reference, and many iterators iterate over
/// references, there can be a possibly confusing situation where the
/// return value is a double reference. You can see this effect in the
/// examples below.
///
/// # Examples
///
/// Basic usage:
///
/// ```
/// let xs = [1, 2, 3];
///
/// let mut iter = xs.iter().peekable();
///
/// // peek() lets us see into the future
/// assert_eq!(iter.peek(), Some(&&1));
/// assert_eq!(iter.next(), Some(&1));
///
/// assert_eq!(iter.next(), Some(&2));
///
/// // The iterator does not advance even if we `peek` multiple times
/// assert_eq!(iter.peek(), Some(&&3));
/// assert_eq!(iter.peek(), Some(&&3));
///
/// assert_eq!(iter.next(), Some(&3));
///
/// // After the iterator is finished, so is `peek()`
/// assert_eq!(iter.peek(), None);
/// assert_eq!(iter.next(), None);
/// ```
#[inline]
#[stable(feature = "rust1", since = "1.0.0")]
pub fn peek(&mut self) -> Option<&I::Item> {
let iter = &mut self.iter;
self.peeked.get_or_insert_with(|| iter.next()).as_ref()
}
/// Consume and return the next value of this iterator if a condition is true.
///
/// If `func` returns `true` for the next value of this iterator, consume and return it.
/// Otherwise, return `None`.
///
/// # Examples
/// Consume a number if it's equal to 0.
/// ```
/// #![feature(peekable_next_if)]
/// let mut iter = (0..5).peekable();
/// // The first item of the iterator is 0; consume it.
/// assert_eq!(iter.next_if(|&x| x == 0), Some(0));
/// // The next item returned is now 1, so `consume` will return `false`.
/// assert_eq!(iter.next_if(|&x| x == 0), None);
/// // `next_if` saves the value of the next item if it was not equal to `expected`.
/// assert_eq!(iter.next(), Some(1));
/// ```
///
/// Consume any number less than 10.
/// ```
/// #![feature(peekable_next_if)]
/// let mut iter = (1..20).peekable();
/// // Consume all numbers less than 10
/// while iter.next_if(|&x| x < 10).is_some() {}
/// // The next value returned will be 10
/// assert_eq!(iter.next(), Some(10));
/// ```
#[unstable(feature = "peekable_next_if", issue = "72480")]
pub fn next_if(&mut self, func: impl FnOnce(&I::Item) -> bool) -> Option<I::Item> {
match self.next() {
Some(matched) if func(&matched) => Some(matched),
other => {
// Since we called `self.next()`, we consumed `self.peeked`.
assert!(self.peeked.is_none());
self.peeked = Some(other);
None
}
}
}
/// Consume and return the next item if it is equal to `expected`.
///
/// # Example
/// Consume a number if it's equal to 0.
/// ```
/// #![feature(peekable_next_if)]
/// let mut iter = (0..5).peekable();
/// // The first item of the iterator is 0; consume it.
/// assert_eq!(iter.next_if_eq(&0), Some(0));
/// // The next item returned is now 1, so `consume` will return `false`.
/// assert_eq!(iter.next_if_eq(&0), None);
/// // `next_if_eq` saves the value of the next item if it was not equal to `expected`.
/// assert_eq!(iter.next(), Some(1));
/// ```
#[unstable(feature = "peekable_next_if", issue = "72480")]
pub fn next_if_eq<T>(&mut self, expected: &T) -> Option<I::Item>
where
T: ?Sized,
I::Item: PartialEq<T>,
{
self.next_if(|next| next == expected)
}
}
#[unstable(feature = "trusted_len", issue = "37572")]
unsafe impl<I> TrustedLen for Peekable<I> where I: TrustedLen {}
#[unstable(issue = "none", feature = "inplace_iteration")]
unsafe impl<S: Iterator, I: Iterator> SourceIter for Peekable<I>
where
I: SourceIter<Source = S>,
{
type Source = S;
#[inline]
unsafe fn as_inner(&mut self) -> &mut S {
// SAFETY: unsafe function forwarding to unsafe function with the same requirements
unsafe { SourceIter::as_inner(&mut self.iter) }
}
}
#[unstable(issue = "none", feature = "inplace_iteration")]
unsafe impl<I: InPlaceIterable> InPlaceIterable for Peekable<I> {}

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use crate::iter::{FusedIterator, TrustedLen};
use crate::ops::Try;
/// A double-ended iterator with the direction inverted.
///
/// This `struct` is created by the [`rev`] method on [`Iterator`]. See its
/// documentation for more.
///
/// [`rev`]: Iterator::rev
/// [`Iterator`]: trait.Iterator.html
#[derive(Clone, Debug)]
#[must_use = "iterators are lazy and do nothing unless consumed"]
#[stable(feature = "rust1", since = "1.0.0")]
pub struct Rev<T> {
iter: T,
}
impl<T> Rev<T> {
pub(in crate::iter) fn new(iter: T) -> Rev<T> {
Rev { iter }
}
}
#[stable(feature = "rust1", since = "1.0.0")]
impl<I> Iterator for Rev<I>
where
I: DoubleEndedIterator,
{
type Item = <I as Iterator>::Item;
#[inline]
fn next(&mut self) -> Option<<I as Iterator>::Item> {
self.iter.next_back()
}
#[inline]
fn size_hint(&self) -> (usize, Option<usize>) {
self.iter.size_hint()
}
#[inline]
fn advance_by(&mut self, n: usize) -> Result<(), usize> {
self.iter.advance_back_by(n)
}
#[inline]
fn nth(&mut self, n: usize) -> Option<<I as Iterator>::Item> {
self.iter.nth_back(n)
}
fn try_fold<B, F, R>(&mut self, init: B, f: F) -> R
where
Self: Sized,
F: FnMut(B, Self::Item) -> R,
R: Try<Ok = B>,
{
self.iter.try_rfold(init, f)
}
fn fold<Acc, F>(self, init: Acc, f: F) -> Acc
where
F: FnMut(Acc, Self::Item) -> Acc,
{
self.iter.rfold(init, f)
}
#[inline]
fn find<P>(&mut self, predicate: P) -> Option<Self::Item>
where
P: FnMut(&Self::Item) -> bool,
{
self.iter.rfind(predicate)
}
}
#[stable(feature = "rust1", since = "1.0.0")]
impl<I> DoubleEndedIterator for Rev<I>
where
I: DoubleEndedIterator,
{
#[inline]
fn next_back(&mut self) -> Option<<I as Iterator>::Item> {
self.iter.next()
}
#[inline]
fn advance_back_by(&mut self, n: usize) -> Result<(), usize> {
self.iter.advance_by(n)
}
#[inline]
fn nth_back(&mut self, n: usize) -> Option<<I as Iterator>::Item> {
self.iter.nth(n)
}
fn try_rfold<B, F, R>(&mut self, init: B, f: F) -> R
where
Self: Sized,
F: FnMut(B, Self::Item) -> R,
R: Try<Ok = B>,
{
self.iter.try_fold(init, f)
}
fn rfold<Acc, F>(self, init: Acc, f: F) -> Acc
where
F: FnMut(Acc, Self::Item) -> Acc,
{
self.iter.fold(init, f)
}
fn rfind<P>(&mut self, predicate: P) -> Option<Self::Item>
where
P: FnMut(&Self::Item) -> bool,
{
self.iter.find(predicate)
}
}
#[stable(feature = "rust1", since = "1.0.0")]
impl<I> ExactSizeIterator for Rev<I>
where
I: ExactSizeIterator + DoubleEndedIterator,
{
fn len(&self) -> usize {
self.iter.len()
}
fn is_empty(&self) -> bool {
self.iter.is_empty()
}
}
#[stable(feature = "fused", since = "1.26.0")]
impl<I> FusedIterator for Rev<I> where I: FusedIterator + DoubleEndedIterator {}
#[unstable(feature = "trusted_len", issue = "37572")]
unsafe impl<I> TrustedLen for Rev<I> where I: TrustedLen + DoubleEndedIterator {}

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use crate::fmt;
use crate::iter::{adapters::SourceIter, InPlaceIterable};
use crate::ops::{ControlFlow, Try};
/// An iterator to maintain state while iterating another iterator.
///
/// This `struct` is created by the [`scan`] method on [`Iterator`]. See its
/// documentation for more.
///
/// [`scan`]: Iterator::scan
/// [`Iterator`]: trait.Iterator.html
#[must_use = "iterators are lazy and do nothing unless consumed"]
#[stable(feature = "rust1", since = "1.0.0")]
#[derive(Clone)]
pub struct Scan<I, St, F> {
iter: I,
f: F,
state: St,
}
impl<I, St, F> Scan<I, St, F> {
pub(in crate::iter) fn new(iter: I, state: St, f: F) -> Scan<I, St, F> {
Scan { iter, state, f }
}
}
#[stable(feature = "core_impl_debug", since = "1.9.0")]
impl<I: fmt::Debug, St: fmt::Debug, F> fmt::Debug for Scan<I, St, F> {
fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
f.debug_struct("Scan").field("iter", &self.iter).field("state", &self.state).finish()
}
}
#[stable(feature = "rust1", since = "1.0.0")]
impl<B, I, St, F> Iterator for Scan<I, St, F>
where
I: Iterator,
F: FnMut(&mut St, I::Item) -> Option<B>,
{
type Item = B;
#[inline]
fn next(&mut self) -> Option<B> {
let a = self.iter.next()?;
(self.f)(&mut self.state, a)
}
#[inline]
fn size_hint(&self) -> (usize, Option<usize>) {
let (_, upper) = self.iter.size_hint();
(0, upper) // can't know a lower bound, due to the scan function
}
#[inline]
fn try_fold<Acc, Fold, R>(&mut self, init: Acc, fold: Fold) -> R
where
Self: Sized,
Fold: FnMut(Acc, Self::Item) -> R,
R: Try<Ok = Acc>,
{
fn scan<'a, T, St, B, Acc, R: Try<Ok = Acc>>(
state: &'a mut St,
f: &'a mut impl FnMut(&mut St, T) -> Option<B>,
mut fold: impl FnMut(Acc, B) -> R + 'a,
) -> impl FnMut(Acc, T) -> ControlFlow<R, Acc> + 'a {
move |acc, x| match f(state, x) {
None => ControlFlow::Break(try { acc }),
Some(x) => ControlFlow::from_try(fold(acc, x)),
}
}
let state = &mut self.state;
let f = &mut self.f;
self.iter.try_fold(init, scan(state, f, fold)).into_try()
}
#[inline]
fn fold<Acc, Fold>(mut self, init: Acc, fold: Fold) -> Acc
where
Self: Sized,
Fold: FnMut(Acc, Self::Item) -> Acc,
{
#[inline]
fn ok<B, T>(mut f: impl FnMut(B, T) -> B) -> impl FnMut(B, T) -> Result<B, !> {
move |acc, x| Ok(f(acc, x))
}
self.try_fold(init, ok(fold)).unwrap()
}
}
#[unstable(issue = "none", feature = "inplace_iteration")]
unsafe impl<St, F, B, S: Iterator, I: Iterator> SourceIter for Scan<I, St, F>
where
I: SourceIter<Source = S>,
F: FnMut(&mut St, I::Item) -> Option<B>,
{
type Source = S;
#[inline]
unsafe fn as_inner(&mut self) -> &mut S {
// SAFETY: unsafe function forwarding to unsafe function with the same requirements
unsafe { SourceIter::as_inner(&mut self.iter) }
}
}
#[unstable(issue = "none", feature = "inplace_iteration")]
unsafe impl<St, F, B, I: InPlaceIterable> InPlaceIterable for Scan<I, St, F> where
F: FnMut(&mut St, I::Item) -> Option<B>
{
}

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use crate::iter::{adapters::SourceIter, FusedIterator, InPlaceIterable};
use crate::ops::{ControlFlow, Try};
/// An iterator that skips over `n` elements of `iter`.
///
/// This `struct` is created by the [`skip`] method on [`Iterator`]. See its
/// documentation for more.
///
/// [`skip`]: Iterator::skip
/// [`Iterator`]: trait.Iterator.html
#[derive(Clone, Debug)]
#[must_use = "iterators are lazy and do nothing unless consumed"]
#[stable(feature = "rust1", since = "1.0.0")]
pub struct Skip<I> {
iter: I,
n: usize,
}
impl<I> Skip<I> {
pub(in crate::iter) fn new(iter: I, n: usize) -> Skip<I> {
Skip { iter, n }
}
}
#[stable(feature = "rust1", since = "1.0.0")]
impl<I> Iterator for Skip<I>
where
I: Iterator,
{
type Item = <I as Iterator>::Item;
#[inline]
fn next(&mut self) -> Option<I::Item> {
if self.n == 0 {
self.iter.next()
} else {
let old_n = self.n;
self.n = 0;
self.iter.nth(old_n)
}
}
#[inline]
fn nth(&mut self, n: usize) -> Option<I::Item> {
// Can't just add n + self.n due to overflow.
if self.n > 0 {
let to_skip = self.n;
self.n = 0;
// nth(n) skips n+1
self.iter.nth(to_skip - 1)?;
}
self.iter.nth(n)
}
#[inline]
fn count(mut self) -> usize {
if self.n > 0 {
// nth(n) skips n+1
if self.iter.nth(self.n - 1).is_none() {
return 0;
}
}
self.iter.count()
}
#[inline]
fn last(mut self) -> Option<I::Item> {
if self.n > 0 {
// nth(n) skips n+1
self.iter.nth(self.n - 1)?;
}
self.iter.last()
}
#[inline]
fn size_hint(&self) -> (usize, Option<usize>) {
let (lower, upper) = self.iter.size_hint();
let lower = lower.saturating_sub(self.n);
let upper = match upper {
Some(x) => Some(x.saturating_sub(self.n)),
None => None,
};
(lower, upper)
}
#[inline]
fn try_fold<Acc, Fold, R>(&mut self, init: Acc, fold: Fold) -> R
where
Self: Sized,
Fold: FnMut(Acc, Self::Item) -> R,
R: Try<Ok = Acc>,
{
let n = self.n;
self.n = 0;
if n > 0 {
// nth(n) skips n+1
if self.iter.nth(n - 1).is_none() {
return try { init };
}
}
self.iter.try_fold(init, fold)
}
#[inline]
fn fold<Acc, Fold>(mut self, init: Acc, fold: Fold) -> Acc
where
Fold: FnMut(Acc, Self::Item) -> Acc,
{
if self.n > 0 {
// nth(n) skips n+1
if self.iter.nth(self.n - 1).is_none() {
return init;
}
}
self.iter.fold(init, fold)
}
}
#[stable(feature = "rust1", since = "1.0.0")]
impl<I> ExactSizeIterator for Skip<I> where I: ExactSizeIterator {}
#[stable(feature = "double_ended_skip_iterator", since = "1.9.0")]
impl<I> DoubleEndedIterator for Skip<I>
where
I: DoubleEndedIterator + ExactSizeIterator,
{
fn next_back(&mut self) -> Option<Self::Item> {
if self.len() > 0 { self.iter.next_back() } else { None }
}
#[inline]
fn nth_back(&mut self, n: usize) -> Option<I::Item> {
let len = self.len();
if n < len {
self.iter.nth_back(n)
} else {
if len > 0 {
// consume the original iterator
self.iter.nth_back(len - 1);
}
None
}
}
fn try_rfold<Acc, Fold, R>(&mut self, init: Acc, fold: Fold) -> R
where
Self: Sized,
Fold: FnMut(Acc, Self::Item) -> R,
R: Try<Ok = Acc>,
{
fn check<T, Acc, R: Try<Ok = Acc>>(
mut n: usize,
mut fold: impl FnMut(Acc, T) -> R,
) -> impl FnMut(Acc, T) -> ControlFlow<R, Acc> {
move |acc, x| {
n -= 1;
let r = fold(acc, x);
if n == 0 { ControlFlow::Break(r) } else { ControlFlow::from_try(r) }
}
}
let n = self.len();
if n == 0 { try { init } } else { self.iter.try_rfold(init, check(n, fold)).into_try() }
}
fn rfold<Acc, Fold>(mut self, init: Acc, fold: Fold) -> Acc
where
Fold: FnMut(Acc, Self::Item) -> Acc,
{
#[inline]
fn ok<Acc, T>(mut f: impl FnMut(Acc, T) -> Acc) -> impl FnMut(Acc, T) -> Result<Acc, !> {
move |acc, x| Ok(f(acc, x))
}
self.try_rfold(init, ok(fold)).unwrap()
}
}
#[stable(feature = "fused", since = "1.26.0")]
impl<I> FusedIterator for Skip<I> where I: FusedIterator {}
#[unstable(issue = "none", feature = "inplace_iteration")]
unsafe impl<S: Iterator, I: Iterator> SourceIter for Skip<I>
where
I: SourceIter<Source = S>,
{
type Source = S;
#[inline]
unsafe fn as_inner(&mut self) -> &mut S {
// SAFETY: unsafe function forwarding to unsafe function with the same requirements
unsafe { SourceIter::as_inner(&mut self.iter) }
}
}
#[unstable(issue = "none", feature = "inplace_iteration")]
unsafe impl<I: InPlaceIterable> InPlaceIterable for Skip<I> {}

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use crate::fmt;
use crate::iter::{adapters::SourceIter, FusedIterator, InPlaceIterable};
use crate::ops::Try;
/// An iterator that rejects elements while `predicate` returns `true`.
///
/// This `struct` is created by the [`skip_while`] method on [`Iterator`]. See its
/// documentation for more.
///
/// [`skip_while`]: Iterator::skip_while
/// [`Iterator`]: trait.Iterator.html
#[must_use = "iterators are lazy and do nothing unless consumed"]
#[stable(feature = "rust1", since = "1.0.0")]
#[derive(Clone)]
pub struct SkipWhile<I, P> {
iter: I,
flag: bool,
predicate: P,
}
impl<I, P> SkipWhile<I, P> {
pub(in crate::iter) fn new(iter: I, predicate: P) -> SkipWhile<I, P> {
SkipWhile { iter, flag: false, predicate }
}
}
#[stable(feature = "core_impl_debug", since = "1.9.0")]
impl<I: fmt::Debug, P> fmt::Debug for SkipWhile<I, P> {
fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
f.debug_struct("SkipWhile").field("iter", &self.iter).field("flag", &self.flag).finish()
}
}
#[stable(feature = "rust1", since = "1.0.0")]
impl<I: Iterator, P> Iterator for SkipWhile<I, P>
where
P: FnMut(&I::Item) -> bool,
{
type Item = I::Item;
#[inline]
fn next(&mut self) -> Option<I::Item> {
fn check<'a, T>(
flag: &'a mut bool,
pred: &'a mut impl FnMut(&T) -> bool,
) -> impl FnMut(&T) -> bool + 'a {
move |x| {
if *flag || !pred(x) {
*flag = true;
true
} else {
false
}
}
}
let flag = &mut self.flag;
let pred = &mut self.predicate;
self.iter.find(check(flag, pred))
}
#[inline]
fn size_hint(&self) -> (usize, Option<usize>) {
let (_, upper) = self.iter.size_hint();
(0, upper) // can't know a lower bound, due to the predicate
}
#[inline]
fn try_fold<Acc, Fold, R>(&mut self, mut init: Acc, mut fold: Fold) -> R
where
Self: Sized,
Fold: FnMut(Acc, Self::Item) -> R,
R: Try<Ok = Acc>,
{
if !self.flag {
match self.next() {
Some(v) => init = fold(init, v)?,
None => return try { init },
}
}
self.iter.try_fold(init, fold)
}
#[inline]
fn fold<Acc, Fold>(mut self, mut init: Acc, mut fold: Fold) -> Acc
where
Fold: FnMut(Acc, Self::Item) -> Acc,
{
if !self.flag {
match self.next() {
Some(v) => init = fold(init, v),
None => return init,
}
}
self.iter.fold(init, fold)
}
}
#[stable(feature = "fused", since = "1.26.0")]
impl<I, P> FusedIterator for SkipWhile<I, P>
where
I: FusedIterator,
P: FnMut(&I::Item) -> bool,
{
}
#[unstable(issue = "none", feature = "inplace_iteration")]
unsafe impl<S: Iterator, P, I: Iterator> SourceIter for SkipWhile<I, P>
where
P: FnMut(&I::Item) -> bool,
I: SourceIter<Source = S>,
{
type Source = S;
#[inline]
unsafe fn as_inner(&mut self) -> &mut S {
// SAFETY: unsafe function forwarding to unsafe function with the same requirements
unsafe { SourceIter::as_inner(&mut self.iter) }
}
}
#[unstable(issue = "none", feature = "inplace_iteration")]
unsafe impl<I: InPlaceIterable, F> InPlaceIterable for SkipWhile<I, F> where
F: FnMut(&I::Item) -> bool
{
}

235
library/core/src/iter/adapters/step_by.rs Normal file
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@ -0,0 +1,235 @@
use crate::{intrinsics, iter::from_fn, ops::Try};
/// An iterator for stepping iterators by a custom amount.
///
/// This `struct` is created by the [`step_by`] method on [`Iterator`]. See
/// its documentation for more.
///
/// [`step_by`]: Iterator::step_by
/// [`Iterator`]: trait.Iterator.html
#[must_use = "iterators are lazy and do nothing unless consumed"]
#[stable(feature = "iterator_step_by", since = "1.28.0")]
#[derive(Clone, Debug)]
pub struct StepBy<I> {
iter: I,
step: usize,
first_take: bool,
}
impl<I> StepBy<I> {
pub(in crate::iter) fn new(iter: I, step: usize) -> StepBy<I> {
assert!(step != 0);
StepBy { iter, step: step - 1, first_take: true }
}
}
#[stable(feature = "iterator_step_by", since = "1.28.0")]
impl<I> Iterator for StepBy<I>
where
I: Iterator,
{
type Item = I::Item;
#[inline]
fn next(&mut self) -> Option<Self::Item> {
if self.first_take {
self.first_take = false;
self.iter.next()
} else {
self.iter.nth(self.step)
}
}
#[inline]
fn size_hint(&self) -> (usize, Option<usize>) {
#[inline]
fn first_size(step: usize) -> impl Fn(usize) -> usize {
move |n| if n == 0 { 0 } else { 1 + (n - 1) / (step + 1) }
}
#[inline]
fn other_size(step: usize) -> impl Fn(usize) -> usize {
move |n| n / (step + 1)
}
let (low, high) = self.iter.size_hint();
if self.first_take {
let f = first_size(self.step);
(f(low), high.map(f))
} else {
let f = other_size(self.step);
(f(low), high.map(f))
}
}
#[inline]
fn nth(&mut self, mut n: usize) -> Option<Self::Item> {
if self.first_take {
self.first_take = false;
let first = self.iter.next();
if n == 0 {
return first;
}
n -= 1;
}
// n and self.step are indices, we need to add 1 to get the amount of elements
// When calling `.nth`, we need to subtract 1 again to convert back to an index
// step + 1 can't overflow because `.step_by` sets `self.step` to `step - 1`
let mut step = self.step + 1;
// n + 1 could overflow
// thus, if n is usize::MAX, instead of adding one, we call .nth(step)
if n == usize::MAX {
self.iter.nth(step - 1);
} else {
n += 1;
}
// overflow handling
loop {
let mul = n.checked_mul(step);
{
if intrinsics::likely(mul.is_some()) {
return self.iter.nth(mul.unwrap() - 1);
}
}
let div_n = usize::MAX / n;
let div_step = usize::MAX / step;
let nth_n = div_n * n;
let nth_step = div_step * step;
let nth = if nth_n > nth_step {
step -= div_n;
nth_n
} else {
n -= div_step;
nth_step
};
self.iter.nth(nth - 1);
}
}
fn try_fold<Acc, F, R>(&mut self, mut acc: Acc, mut f: F) -> R
where
F: FnMut(Acc, Self::Item) -> R,
R: Try<Ok = Acc>,
{
#[inline]
fn nth<I: Iterator>(iter: &mut I, step: usize) -> impl FnMut() -> Option<I::Item> + '_ {
move || iter.nth(step)
}
if self.first_take {
self.first_take = false;
match self.iter.next() {
None => return try { acc },
Some(x) => acc = f(acc, x)?,
}
}
from_fn(nth(&mut self.iter, self.step)).try_fold(acc, f)
}
fn fold<Acc, F>(mut self, mut acc: Acc, mut f: F) -> Acc
where
F: FnMut(Acc, Self::Item) -> Acc,
{
#[inline]
fn nth<I: Iterator>(iter: &mut I, step: usize) -> impl FnMut() -> Option<I::Item> + '_ {
move || iter.nth(step)
}
if self.first_take {
self.first_take = false;
match self.iter.next() {
None => return acc,
Some(x) => acc = f(acc, x),
}
}
from_fn(nth(&mut self.iter, self.step)).fold(acc, f)
}
}
impl<I> StepBy<I>
where
I: ExactSizeIterator,
{
// The zero-based index starting from the end of the iterator of the
// last element. Used in the `DoubleEndedIterator` implementation.
fn next_back_index(&self) -> usize {
let rem = self.iter.len() % (self.step + 1);
if self.first_take {
if rem == 0 { self.step } else { rem - 1 }
} else {
rem
}
}
}
#[stable(feature = "double_ended_step_by_iterator", since = "1.38.0")]
impl<I> DoubleEndedIterator for StepBy<I>
where
I: DoubleEndedIterator + ExactSizeIterator,
{
#[inline]
fn next_back(&mut self) -> Option<Self::Item> {
self.iter.nth_back(self.next_back_index())
}
#[inline]
fn nth_back(&mut self, n: usize) -> Option<Self::Item> {
// `self.iter.nth_back(usize::MAX)` does the right thing here when `n`
// is out of bounds because the length of `self.iter` does not exceed
// `usize::MAX` (because `I: ExactSizeIterator`) and `nth_back` is
// zero-indexed
let n = n.saturating_mul(self.step + 1).saturating_add(self.next_back_index());
self.iter.nth_back(n)
}
fn try_rfold<Acc, F, R>(&mut self, init: Acc, mut f: F) -> R
where
F: FnMut(Acc, Self::Item) -> R,
R: Try<Ok = Acc>,
{
#[inline]
fn nth_back<I: DoubleEndedIterator>(
iter: &mut I,
step: usize,
) -> impl FnMut() -> Option<I::Item> + '_ {
move || iter.nth_back(step)
}
match self.next_back() {
None => try { init },
Some(x) => {
let acc = f(init, x)?;
from_fn(nth_back(&mut self.iter, self.step)).try_fold(acc, f)
}
}
}
#[inline]
fn rfold<Acc, F>(mut self, init: Acc, mut f: F) -> Acc
where
Self: Sized,
F: FnMut(Acc, Self::Item) -> Acc,
{
#[inline]
fn nth_back<I: DoubleEndedIterator>(
iter: &mut I,
step: usize,
) -> impl FnMut() -> Option<I::Item> + '_ {
move || iter.nth_back(step)
}
match self.next_back() {
None => init,
Some(x) => {
let acc = f(init, x);
from_fn(nth_back(&mut self.iter, self.step)).fold(acc, f)
}
}
}
}
// StepBy can only make the iterator shorter, so the len will still fit.
#[stable(feature = "iterator_step_by", since = "1.28.0")]
impl<I> ExactSizeIterator for StepBy<I> where I: ExactSizeIterator {}

209
library/core/src/iter/adapters/take.rs Normal file
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@ -0,0 +1,209 @@
use crate::cmp;
use crate::iter::{adapters::SourceIter, FusedIterator, InPlaceIterable, TrustedLen};
use crate::ops::{ControlFlow, Try};
/// An iterator that only iterates over the first `n` iterations of `iter`.
///
/// This `struct` is created by the [`take`] method on [`Iterator`]. See its
/// documentation for more.
///
/// [`take`]: Iterator::take
/// [`Iterator`]: trait.Iterator.html
#[derive(Clone, Debug)]
#[must_use = "iterators are lazy and do nothing unless consumed"]
#[stable(feature = "rust1", since = "1.0.0")]
pub struct Take<I> {
iter: I,
n: usize,
}
impl<I> Take<I> {
pub(in crate::iter) fn new(iter: I, n: usize) -> Take<I> {
Take { iter, n }
}
}
#[stable(feature = "rust1", since = "1.0.0")]
impl<I> Iterator for Take<I>
where
I: Iterator,
{
type Item = <I as Iterator>::Item;
#[inline]
fn next(&mut self) -> Option<<I as Iterator>::Item> {
if self.n != 0 {
self.n -= 1;
self.iter.next()
} else {
None
}
}
#[inline]
fn nth(&mut self, n: usize) -> Option<I::Item> {
if self.n > n {
self.n -= n + 1;
self.iter.nth(n)
} else {
if self.n > 0 {
self.iter.nth(self.n - 1);
self.n = 0;
}
None
}
}
#[inline]
fn size_hint(&self) -> (usize, Option<usize>) {
if self.n == 0 {
return (0, Some(0));
}
let (lower, upper) = self.iter.size_hint();
let lower = cmp::min(lower, self.n);
let upper = match upper {
Some(x) if x < self.n => Some(x),
_ => Some(self.n),
};
(lower, upper)
}
#[inline]
fn try_fold<Acc, Fold, R>(&mut self, init: Acc, fold: Fold) -> R
where
Self: Sized,
Fold: FnMut(Acc, Self::Item) -> R,
R: Try<Ok = Acc>,
{
fn check<'a, T, Acc, R: Try<Ok = Acc>>(
n: &'a mut usize,
mut fold: impl FnMut(Acc, T) -> R + 'a,
) -> impl FnMut(Acc, T) -> ControlFlow<R, Acc> + 'a {
move |acc, x| {
*n -= 1;
let r = fold(acc, x);
if *n == 0 { ControlFlow::Break(r) } else { ControlFlow::from_try(r) }
}
}
if self.n == 0 {
try { init }
} else {
let n = &mut self.n;
self.iter.try_fold(init, check(n, fold)).into_try()
}
}
#[inline]
fn fold<Acc, Fold>(mut self, init: Acc, fold: Fold) -> Acc
where
Self: Sized,
Fold: FnMut(Acc, Self::Item) -> Acc,
{
#[inline]
fn ok<B, T>(mut f: impl FnMut(B, T) -> B) -> impl FnMut(B, T) -> Result<B, !> {
move |acc, x| Ok(f(acc, x))
}
self.try_fold(init, ok(fold)).unwrap()
}
}
#[unstable(issue = "none", feature = "inplace_iteration")]
unsafe impl<S: Iterator, I: Iterator> SourceIter for Take<I>
where
I: SourceIter<Source = S>,
{
type Source = S;
#[inline]
unsafe fn as_inner(&mut self) -> &mut S {
// SAFETY: unsafe function forwarding to unsafe function with the same requirements
unsafe { SourceIter::as_inner(&mut self.iter) }
}
}
#[unstable(issue = "none", feature = "inplace_iteration")]
unsafe impl<I: InPlaceIterable> InPlaceIterable for Take<I> {}
#[stable(feature = "double_ended_take_iterator", since = "1.38.0")]
impl<I> DoubleEndedIterator for Take<I>
where
I: DoubleEndedIterator + ExactSizeIterator,
{
#[inline]
fn next_back(&mut self) -> Option<Self::Item> {
if self.n == 0 {
None
} else {
let n = self.n;
self.n -= 1;
self.iter.nth_back(self.iter.len().saturating_sub(n))
}
}
#[inline]
fn nth_back(&mut self, n: usize) -> Option<Self::Item> {
let len = self.iter.len();
if self.n > n {
let m = len.saturating_sub(self.n) + n;
self.n -= n + 1;
self.iter.nth_back(m)
} else {
if len > 0 {
self.iter.nth_back(len - 1);
}
None
}
}
#[inline]
fn try_rfold<Acc, Fold, R>(&mut self, init: Acc, fold: Fold) -> R
where
Self: Sized,
Fold: FnMut(Acc, Self::Item) -> R,
R: Try<Ok = Acc>,
{
if self.n == 0 {
try { init }
} else {
let len = self.iter.len();
if len > self.n && self.iter.nth_back(len - self.n - 1).is_none() {
try { init }
} else {
self.iter.try_rfold(init, fold)
}
}
}
#[inline]
fn rfold<Acc, Fold>(mut self, init: Acc, fold: Fold) -> Acc
where
Self: Sized,
Fold: FnMut(Acc, Self::Item) -> Acc,
{
if self.n == 0 {
init
} else {
let len = self.iter.len();
if len > self.n && self.iter.nth_back(len - self.n - 1).is_none() {
init
} else {
self.iter.rfold(init, fold)
}
}
}
}
#[stable(feature = "rust1", since = "1.0.0")]
impl<I> ExactSizeIterator for Take<I> where I: ExactSizeIterator {}
#[stable(feature = "fused", since = "1.26.0")]
impl<I> FusedIterator for Take<I> where I: FusedIterator {}
#[unstable(feature = "trusted_len", issue = "37572")]
unsafe impl<I: TrustedLen> TrustedLen for Take<I> {}

139
library/core/src/iter/adapters/take_while.rs Normal file
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@ -0,0 +1,139 @@
use crate::fmt;
use crate::iter::{adapters::SourceIter, FusedIterator, InPlaceIterable};
use crate::ops::{ControlFlow, Try};
/// An iterator that only accepts elements while `predicate` returns `true`.
///
/// This `struct` is created by the [`take_while`] method on [`Iterator`]. See its
/// documentation for more.
///
/// [`take_while`]: Iterator::take_while
/// [`Iterator`]: trait.Iterator.html
#[must_use = "iterators are lazy and do nothing unless consumed"]
#[stable(feature = "rust1", since = "1.0.0")]
#[derive(Clone)]
pub struct TakeWhile<I, P> {
iter: I,
flag: bool,
predicate: P,
}
impl<I, P> TakeWhile<I, P> {
pub(in crate::iter) fn new(iter: I, predicate: P) -> TakeWhile<I, P> {
TakeWhile { iter, flag: false, predicate }
}
}
#[stable(feature = "core_impl_debug", since = "1.9.0")]
impl<I: fmt::Debug, P> fmt::Debug for TakeWhile<I, P> {
fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
f.debug_struct("TakeWhile").field("iter", &self.iter).field("flag", &self.flag).finish()
}
}
#[stable(feature = "rust1", since = "1.0.0")]
impl<I: Iterator, P> Iterator for TakeWhile<I, P>
where
P: FnMut(&I::Item) -> bool,
{
type Item = I::Item;
#[inline]
fn next(&mut self) -> Option<I::Item> {
if self.flag {
None
} else {
let x = self.iter.next()?;
if (self.predicate)(&x) {
Some(x)
} else {
self.flag = true;
None
}
}
}
#[inline]
fn size_hint(&self) -> (usize, Option<usize>) {
if self.flag {
(0, Some(0))
} else {
let (_, upper) = self.iter.size_hint();
(0, upper) // can't know a lower bound, due to the predicate
}
}
#[inline]
fn try_fold<Acc, Fold, R>(&mut self, init: Acc, fold: Fold) -> R
where
Self: Sized,
Fold: FnMut(Acc, Self::Item) -> R,
R: Try<Ok = Acc>,
{
fn check<'a, T, Acc, R: Try<Ok = Acc>>(
flag: &'a mut bool,
p: &'a mut impl FnMut(&T) -> bool,
mut fold: impl FnMut(Acc, T) -> R + 'a,
) -> impl FnMut(Acc, T) -> ControlFlow<R, Acc> + 'a {
move |acc, x| {
if p(&x) {
ControlFlow::from_try(fold(acc, x))
} else {
*flag = true;
ControlFlow::Break(try { acc })
}
}
}
if self.flag {
try { init }
} else {
let flag = &mut self.flag;
let p = &mut self.predicate;
self.iter.try_fold(init, check(flag, p, fold)).into_try()
}
}
#[inline]
fn fold<Acc, Fold>(mut self, init: Acc, fold: Fold) -> Acc
where
Self: Sized,
Fold: FnMut(Acc, Self::Item) -> Acc,
{
#[inline]
fn ok<B, T>(mut f: impl FnMut(B, T) -> B) -> impl FnMut(B, T) -> Result<B, !> {
move |acc, x| Ok(f(acc, x))
}
self.try_fold(init, ok(fold)).unwrap()
}
}
#[stable(feature = "fused", since = "1.26.0")]
impl<I, P> FusedIterator for TakeWhile<I, P>
where
I: FusedIterator,
P: FnMut(&I::Item) -> bool,
{
}
#[unstable(issue = "none", feature = "inplace_iteration")]
unsafe impl<S: Iterator, P, I: Iterator> SourceIter for TakeWhile<I, P>
where
P: FnMut(&I::Item) -> bool,
I: SourceIter<Source = S>,
{
type Source = S;
#[inline]
unsafe fn as_inner(&mut self) -> &mut S {
// SAFETY: unsafe function forwarding to unsafe function with the same requirements
unsafe { SourceIter::as_inner(&mut self.iter) }
}
}
#[unstable(issue = "none", feature = "inplace_iteration")]
unsafe impl<I: InPlaceIterable, F> InPlaceIterable for TakeWhile<I, F> where
F: FnMut(&I::Item) -> bool
{
}

9
library/core/src/iter/adapters/zip.rs
View File

@ -1,10 +1,7 @@
use crate::cmp;
use crate::fmt::{self, Debug};
use super::super::{
DoubleEndedIterator, ExactSizeIterator, FusedIterator, InPlaceIterable, Iterator, SourceIter,
TrustedLen,
};
use crate::iter::{DoubleEndedIterator, ExactSizeIterator, FusedIterator, Iterator};
use crate::iter::{InPlaceIterable, SourceIter, TrustedLen};
/// An iterator that iterates two other iterators simultaneously.
///
@ -21,7 +18,7 @@ pub struct Zip<A, B> {
len: usize,
}
impl<A: Iterator, B: Iterator> Zip<A, B> {
pub(in super::super) fn new(a: A, b: B) -> Zip<A, B> {
pub(in crate::iter) fn new(a: A, b: B) -> Zip<A, B> {
ZipImpl::new(a, b)
}
fn super_nth(&mut self, mut n: usize) -> Option<(A::Item, B::Item)> {

23
library/core/src/iter/mod.rs
View File

@ -335,15 +335,14 @@ pub use self::sources::{successors, Successors};
#[stable(feature = "fused", since = "1.26.0")]
pub use self::traits::FusedIterator;
#[unstable(issue = "none", feature = "inplace_iteration")]
pub use self::traits::InPlaceIterable;
#[unstable(feature = "trusted_len", issue = "37572")]
pub use self::traits::TrustedLen;
#[stable(feature = "rust1", since = "1.0.0")]
pub use self::traits::{DoubleEndedIterator, Extend, FromIterator, IntoIterator};
#[stable(feature = "rust1", since = "1.0.0")]
pub use self::traits::{ExactSizeIterator, Product, Sum};
#[unstable(issue = "none", feature = "inplace_iteration")]
pub use self::traits::InPlaceIterable;
pub use self::traits::{
DoubleEndedIterator, ExactSizeIterator, Extend, FromIterator, IntoIterator, Product, Sum,
};
#[stable(feature = "iter_cloned", since = "1.1.0")]
pub use self::adapters::Cloned;
@ -351,21 +350,19 @@ pub use self::adapters::Cloned;
pub use self::adapters::Copied;
#[stable(feature = "iterator_flatten", since = "1.29.0")]
pub use self::adapters::Flatten;
#[unstable(feature = "iter_map_while", reason = "recently added", issue = "68537")]
pub use self::adapters::MapWhile;
#[unstable(issue = "none", feature = "inplace_iteration")]
#[unstable(feature = "inplace_iteration", issue = "none")]
pub use self::adapters::SourceIter;
#[stable(feature = "iterator_step_by", since = "1.28.0")]
pub use self::adapters::StepBy;
#[unstable(feature = "trusted_random_access", issue = "none")]
pub use self::adapters::TrustedRandomAccess;
#[stable(feature = "rust1", since = "1.0.0")]
pub use self::adapters::{Chain, Cycle, Enumerate, Filter, FilterMap, Map, Rev, Zip};
#[stable(feature = "rust1", since = "1.0.0")]
pub use self::adapters::{FlatMap, Peekable, Scan, Skip, SkipWhile, Take, TakeWhile};
#[stable(feature = "rust1", since = "1.0.0")]
pub use self::adapters::{Fuse, Inspect};
pub use self::adapters::{
Chain, Cycle, Enumerate, Filter, FilterMap, FlatMap, Fuse, Inspect, Map, Peekable, Rev, Scan,
Skip, SkipWhile, Take, TakeWhile, Zip,
};
pub(crate) use self::adapters::process_results;

632
library/core/src/iter/sources.rs
View File

@ -1,625 +1,27 @@
use crate::fmt;
use crate::marker;
mod empty;
mod from_fn;
mod once;
mod once_with;
mod repeat;
mod repeat_with;
mod successors;
use super::{FusedIterator, TrustedLen};
pub use self::repeat::{repeat, Repeat};
/// An iterator that repeats an element endlessly.
///
/// This `struct` is created by the [`repeat()`] function. See its documentation for more.
#[derive(Clone, Debug)]
#[stable(feature = "rust1", since = "1.0.0")]
pub struct Repeat<A> {
element: A,
}
#[stable(feature = "iter_empty", since = "1.2.0")]
pub use self::empty::{empty, Empty};
#[stable(feature = "rust1", since = "1.0.0")]
impl<A: Clone> Iterator for Repeat<A> {
type Item = A;
#[inline]
fn next(&mut self) -> Option<A> {
Some(self.element.clone())
}
#[inline]
fn size_hint(&self) -> (usize, Option<usize>) {
(usize::MAX, None)
}
}
#[stable(feature = "rust1", since = "1.0.0")]
impl<A: Clone> DoubleEndedIterator for Repeat<A> {
#[inline]
fn next_back(&mut self) -> Option<A> {
Some(self.element.clone())
}
}
#[stable(feature = "fused", since = "1.26.0")]
impl<A: Clone> FusedIterator for Repeat<A> {}
#[unstable(feature = "trusted_len", issue = "37572")]
unsafe impl<A: Clone> TrustedLen for Repeat<A> {}
/// Creates a new iterator that endlessly repeats a single element.
///
/// The `repeat()` function repeats a single value over and over again.
///
/// Infinite iterators like `repeat()` are often used with adapters like
/// [`Iterator::take()`], in order to make them finite.
///
/// If the element type of the iterator you need does not implement `Clone`,
/// or if you do not want to keep the repeated element in memory, you can
/// instead use the [`repeat_with()`] function.
///
/// # Examples
///
/// Basic usage:
///
/// ```
/// use std::iter;
///
/// // the number four 4ever:
/// let mut fours = iter::repeat(4);
///
/// assert_eq!(Some(4), fours.next());
/// assert_eq!(Some(4), fours.next());
/// assert_eq!(Some(4), fours.next());
/// assert_eq!(Some(4), fours.next());
/// assert_eq!(Some(4), fours.next());
///
/// // yup, still four
/// assert_eq!(Some(4), fours.next());
/// ```
///
/// Going finite with [`Iterator::take()`]:
///
/// ```
/// use std::iter;
///
/// // that last example was too many fours. Let's only have four fours.
/// let mut four_fours = iter::repeat(4).take(4);
///
/// assert_eq!(Some(4), four_fours.next());
/// assert_eq!(Some(4), four_fours.next());
/// assert_eq!(Some(4), four_fours.next());
/// assert_eq!(Some(4), four_fours.next());
///
/// // ... and now we're done
/// assert_eq!(None, four_fours.next());
/// ```
#[inline]
#[stable(feature = "rust1", since = "1.0.0")]
pub fn repeat<T: Clone>(elt: T) -> Repeat<T> {
Repeat { element: elt }
}
/// An iterator that repeats elements of type `A` endlessly by
/// applying the provided closure `F: FnMut() -> A`.
///
/// This `struct` is created by the [`repeat_with()`] function.
/// See its documentation for more.
#[derive(Copy, Clone, Debug)]
#[stable(feature = "iterator_repeat_with", since = "1.28.0")]
pub struct RepeatWith<F> {
repeater: F,
}
#[stable(feature = "iter_once", since = "1.2.0")]
pub use self::once::{once, Once};
#[stable(feature = "iterator_repeat_with", since = "1.28.0")]
impl<A, F: FnMut() -> A> Iterator for RepeatWith<F> {
type Item = A;
#[inline]
fn next(&mut self) -> Option<A> {
Some((self.repeater)())
}
#[inline]
fn size_hint(&self) -> (usize, Option<usize>) {
(usize::MAX, None)
}
}
#[stable(feature = "iterator_repeat_with", since = "1.28.0")]
impl<A, F: FnMut() -> A> FusedIterator for RepeatWith<F> {}
#[unstable(feature = "trusted_len", issue = "37572")]
unsafe impl<A, F: FnMut() -> A> TrustedLen for RepeatWith<F> {}
/// Creates a new iterator that repeats elements of type `A` endlessly by
/// applying the provided closure, the repeater, `F: FnMut() -> A`.
///
/// The `repeat_with()` function calls the repeater over and over again.
///
/// Infinite iterators like `repeat_with()` are often used with adapters like
/// [`Iterator::take()`], in order to make them finite.
///
/// If the element type of the iterator you need implements [`Clone`], and
/// it is OK to keep the source element in memory, you should instead use
/// the [`repeat()`] function.
///
/// An iterator produced by `repeat_with()` is not a [`DoubleEndedIterator`].
/// If you need `repeat_with()` to return a [`DoubleEndedIterator`],
/// please open a GitHub issue explaining your use case.
///
/// [`DoubleEndedIterator`]: crate::iter::DoubleEndedIterator
///
/// # Examples
///
/// Basic usage:
///
/// ```
/// use std::iter;
///
/// // let's assume we have some value of a type that is not `Clone`
/// // or which don't want to have in memory just yet because it is expensive:
/// #[derive(PartialEq, Debug)]
/// struct Expensive;
///
/// // a particular value forever:
/// let mut things = iter::repeat_with(|| Expensive);
///
/// assert_eq!(Some(Expensive), things.next());
/// assert_eq!(Some(Expensive), things.next());
/// assert_eq!(Some(Expensive), things.next());
/// assert_eq!(Some(Expensive), things.next());
/// assert_eq!(Some(Expensive), things.next());
/// ```
///
/// Using mutation and going finite:
///
/// ```rust
/// use std::iter;
///
/// // From the zeroth to the third power of two:
/// let mut curr = 1;
/// let mut pow2 = iter::repeat_with(|| { let tmp = curr; curr *= 2; tmp })
/// .take(4);
///
/// assert_eq!(Some(1), pow2.next());
/// assert_eq!(Some(2), pow2.next());
/// assert_eq!(Some(4), pow2.next());
/// assert_eq!(Some(8), pow2.next());
///
/// // ... and now we're done
/// assert_eq!(None, pow2.next());
/// ```
#[inline]
#[stable(feature = "iterator_repeat_with", since = "1.28.0")]
pub fn repeat_with<A, F: FnMut() -> A>(repeater: F) -> RepeatWith<F> {
RepeatWith { repeater }
}
/// An iterator that yields nothing.
///
/// This `struct` is created by the [`empty()`] function. See its documentation for more.
#[stable(feature = "iter_empty", since = "1.2.0")]
pub struct Empty<T>(marker::PhantomData<T>);
#[stable(feature = "iter_empty_send_sync", since = "1.42.0")]
unsafe impl<T> Send for Empty<T> {}
#[stable(feature = "iter_empty_send_sync", since = "1.42.0")]
unsafe impl<T> Sync for Empty<T> {}
#[stable(feature = "core_impl_debug", since = "1.9.0")]
impl<T> fmt::Debug for Empty<T> {
fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
f.pad("Empty")
}
}
#[stable(feature = "iter_empty", since = "1.2.0")]
impl<T> Iterator for Empty<T> {
type Item = T;
fn next(&mut self) -> Option<T> {
None
}
fn size_hint(&self) -> (usize, Option<usize>) {
(0, Some(0))
}
}
#[stable(feature = "iter_empty", since = "1.2.0")]
impl<T> DoubleEndedIterator for Empty<T> {
fn next_back(&mut self) -> Option<T> {
None
}
}
#[stable(feature = "iter_empty", since = "1.2.0")]
impl<T> ExactSizeIterator for Empty<T> {
fn len(&self) -> usize {
0
}
}
#[unstable(feature = "trusted_len", issue = "37572")]
unsafe impl<T> TrustedLen for Empty<T> {}
#[stable(feature = "fused", since = "1.26.0")]
impl<T> FusedIterator for Empty<T> {}
// not #[derive] because that adds a Clone bound on T,
// which isn't necessary.
#[stable(feature = "iter_empty", since = "1.2.0")]
impl<T> Clone for Empty<T> {
fn clone(&self) -> Empty<T> {
Empty(marker::PhantomData)
}
}
// not #[derive] because that adds a Default bound on T,
// which isn't necessary.
#[stable(feature = "iter_empty", since = "1.2.0")]
impl<T> Default for Empty<T> {
fn default() -> Empty<T> {
Empty(marker::PhantomData)
}
}
/// Creates an iterator that yields nothing.
///
/// # Examples
///
/// Basic usage:
///
/// ```
/// use std::iter;
///
/// // this could have been an iterator over i32, but alas, it's just not.
/// let mut nope = iter::empty::<i32>();
///
/// assert_eq!(None, nope.next());
/// ```
#[stable(feature = "iter_empty", since = "1.2.0")]
#[rustc_const_stable(feature = "const_iter_empty", since = "1.32.0")]
pub const fn empty<T>() -> Empty<T> {
Empty(marker::PhantomData)
}
/// An iterator that yields an element exactly once.
///
/// This `struct` is created by the [`once()`] function. See its documentation for more.
#[derive(Clone, Debug)]
#[stable(feature = "iter_once", since = "1.2.0")]
pub struct Once<T> {
inner: crate::option::IntoIter<T>,
}
#[stable(feature = "iter_once", since = "1.2.0")]
impl<T> Iterator for Once<T> {
type Item = T;
fn next(&mut self) -> Option<T> {
self.inner.next()
}
fn size_hint(&self) -> (usize, Option<usize>) {
self.inner.size_hint()
}
}
#[stable(feature = "iter_once", since = "1.2.0")]
impl<T> DoubleEndedIterator for Once<T> {
fn next_back(&mut self) -> Option<T> {
self.inner.next_back()
}
}
#[stable(feature = "iter_once", since = "1.2.0")]
impl<T> ExactSizeIterator for Once<T> {
fn len(&self) -> usize {
self.inner.len()
}
}
#[unstable(feature = "trusted_len", issue = "37572")]
unsafe impl<T> TrustedLen for Once<T> {}
#[stable(feature = "fused", since = "1.26.0")]
impl<T> FusedIterator for Once<T> {}
/// Creates an iterator that yields an element exactly once.
///
/// This is commonly used to adapt a single value into a [`chain()`] of other
/// kinds of iteration. Maybe you have an iterator that covers almost
/// everything, but you need an extra special case. Maybe you have a function
/// which works on iterators, but you only need to process one value.
///
/// [`chain()`]: Iterator::chain
///
/// # Examples
///
/// Basic usage:
///
/// ```
/// use std::iter;
///
/// // one is the loneliest number
/// let mut one = iter::once(1);
///
/// assert_eq!(Some(1), one.next());
///
/// // just one, that's all we get
/// assert_eq!(None, one.next());
/// ```
///
/// Chaining together with another iterator. Let's say that we want to iterate
/// over each file of the `.foo` directory, but also a configuration file,
/// `.foorc`:
///
/// ```no_run
/// use std::iter;
/// use std::fs;
/// use std::path::PathBuf;
///
/// let dirs = fs::read_dir(".foo").unwrap();
///
/// // we need to convert from an iterator of DirEntry-s to an iterator of
/// // PathBufs, so we use map
/// let dirs = dirs.map(|file| file.unwrap().path());
///
/// // now, our iterator just for our config file
/// let config = iter::once(PathBuf::from(".foorc"));
///
/// // chain the two iterators together into one big iterator
/// let files = dirs.chain(config);
///
/// // this will give us all of the files in .foo as well as .foorc
/// for f in files {
/// println!("{:?}", f);
/// }
/// ```
#[stable(feature = "iter_once", since = "1.2.0")]
pub fn once<T>(value: T) -> Once<T> {
Once { inner: Some(value).into_iter() }
}
/// An iterator that yields a single element of type `A` by
/// applying the provided closure `F: FnOnce() -> A`.
///
/// This `struct` is created by the [`once_with()`] function.
/// See its documentation for more.
#[derive(Clone, Debug)]
#[stable(feature = "iter_once_with", since = "1.43.0")]
pub struct OnceWith<F> {
gen: Option<F>,
}
#[stable(feature = "iter_once_with", since = "1.43.0")]
impl<A, F: FnOnce() -> A> Iterator for OnceWith<F> {
type Item = A;
#[inline]
fn next(&mut self) -> Option<A> {
let f = self.gen.take()?;
Some(f())
}
#[inline]
fn size_hint(&self) -> (usize, Option<usize>) {
self.gen.iter().size_hint()
}
}
#[stable(feature = "iter_once_with", since = "1.43.0")]
impl<A, F: FnOnce() -> A> DoubleEndedIterator for OnceWith<F> {
fn next_back(&mut self) -> Option<A> {
self.next()
}
}
#[stable(feature = "iter_once_with", since = "1.43.0")]
impl<A, F: FnOnce() -> A> ExactSizeIterator for OnceWith<F> {
fn len(&self) -> usize {
self.gen.iter().len()
}
}
#[stable(feature = "iter_once_with", since = "1.43.0")]
impl<A, F: FnOnce() -> A> FusedIterator for OnceWith<F> {}
#[stable(feature = "iter_once_with", since = "1.43.0")]
unsafe impl<A, F: FnOnce() -> A> TrustedLen for OnceWith<F> {}
/// Creates an iterator that lazily generates a value exactly once by invoking
/// the provided closure.
///
/// This is commonly used to adapt a single value generator into a [`chain()`] of
/// other kinds of iteration. Maybe you have an iterator that covers almost
/// everything, but you need an extra special case. Maybe you have a function
/// which works on iterators, but you only need to process one value.
///
/// Unlike [`once()`], this function will lazily generate the value on request.
///
/// [`chain()`]: Iterator::chain
///
/// # Examples
///
/// Basic usage:
///
/// ```
/// use std::iter;
///
/// // one is the loneliest number
/// let mut one = iter::once_with(|| 1);
///
/// assert_eq!(Some(1), one.next());
///
/// // just one, that's all we get
/// assert_eq!(None, one.next());
/// ```
///
/// Chaining together with another iterator. Let's say that we want to iterate
/// over each file of the `.foo` directory, but also a configuration file,
/// `.foorc`:
///
/// ```no_run
/// use std::iter;
/// use std::fs;
/// use std::path::PathBuf;
///
/// let dirs = fs::read_dir(".foo").unwrap();
///
/// // we need to convert from an iterator of DirEntry-s to an iterator of
/// // PathBufs, so we use map
/// let dirs = dirs.map(|file| file.unwrap().path());
///
/// // now, our iterator just for our config file
/// let config = iter::once_with(|| PathBuf::from(".foorc"));
///
/// // chain the two iterators together into one big iterator
/// let files = dirs.chain(config);
///
/// // this will give us all of the files in .foo as well as .foorc
/// for f in files {
/// println!("{:?}", f);
/// }
/// ```
#[inline]
#[stable(feature = "iter_once_with", since = "1.43.0")]
pub fn once_with<A, F: FnOnce() -> A>(gen: F) -> OnceWith<F> {
OnceWith { gen: Some(gen) }
}
/// Creates a new iterator where each iteration calls the provided closure
/// `F: FnMut() -> Option<T>`.
///
/// This allows creating a custom iterator with any behavior
/// without using the more verbose syntax of creating a dedicated type
/// and implementing the [`Iterator`] trait for it.
///
/// Note that the `FromFn` iterator doesn’t make assumptions about the behavior of the closure,
/// and therefore conservatively does not implement [`FusedIterator`],
/// or override [`Iterator::size_hint()`] from its default `(0, None)`.
///
/// The closure can use captures and its environment to track state across iterations. Depending on
/// how the iterator is used, this may require specifying the [`move`] keyword on the closure.
///
/// [`move`]: ../../std/keyword.move.html
///
/// # Examples
///
/// Let’s re-implement the counter iterator from the [module-level documentation]:
///
/// [module-level documentation]: super
///
/// ```
/// let mut count = 0;
/// let counter = std::iter::from_fn(move || {
/// // Increment our count. This is why we started at zero.
/// count += 1;
///
/// // Check to see if we've finished counting or not.
/// if count < 6 {
/// Some(count)
/// } else {
/// None
/// }
/// });
/// assert_eq!(counter.collect::<Vec<_>>(), &[1, 2, 3, 4, 5]);
/// ```
#[inline]
#[stable(feature = "iter_from_fn", since = "1.34.0")]
pub fn from_fn<T, F>(f: F) -> FromFn<F>
where
F: FnMut() -> Option<T>,
{
FromFn(f)
}
/// An iterator where each iteration calls the provided closure `F: FnMut() -> Option<T>`.
///
/// This `struct` is created by the [`iter::from_fn()`] function.
/// See its documentation for more.
///
/// [`iter::from_fn()`]: from_fn
#[derive(Clone)]
#[stable(feature = "iter_from_fn", since = "1.34.0")]
pub struct FromFn<F>(F);
pub use self::repeat_with::{repeat_with, RepeatWith};
#[stable(feature = "iter_from_fn", since = "1.34.0")]
impl<T, F> Iterator for FromFn<F>
where
F: FnMut() -> Option<T>,
{
type Item = T;
#[inline]
fn next(&mut self) -> Option<Self::Item> {
(self.0)()
}
}
#[stable(feature = "iter_from_fn", since = "1.34.0")]
impl<F> fmt::Debug for FromFn<F> {
fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
f.debug_struct("FromFn").finish()
}
}
/// Creates a new iterator where each successive item is computed based on the preceding one.
///
/// The iterator starts with the given first item (if any)
/// and calls the given `FnMut(&T) -> Option<T>` closure to compute each item’s successor.
///
/// ```
/// use std::iter::successors;
///
/// let powers_of_10 = successors(Some(1_u16), |n| n.checked_mul(10));
/// assert_eq!(powers_of_10.collect::<Vec<_>>(), &[1, 10, 100, 1_000, 10_000]);
/// ```
#[stable(feature = "iter_successors", since = "1.34.0")]
pub fn successors<T, F>(first: Option<T>, succ: F) -> Successors<T, F>
where
F: FnMut(&T) -> Option<T>,
{
// If this function returned `impl Iterator<Item=T>`
// it could be based on `unfold` and not need a dedicated type.
// However having a named `Successors<T, F>` type allows it to be `Clone` when `T` and `F` are.
Successors { next: first, succ }
}
/// An new iterator where each successive item is computed based on the preceding one.
///
/// This `struct` is created by the [`iter::successors()`] function.
/// See its documentation for more.
///
/// [`iter::successors()`]: successors
#[derive(Clone)]
#[stable(feature = "iter_successors", since = "1.34.0")]
pub struct Successors<T, F> {
next: Option<T>,
succ: F,
}
pub use self::from_fn::{from_fn, FromFn};
#[stable(feature = "iter_successors", since = "1.34.0")]
impl<T, F> Iterator for Successors<T, F>
where
F: FnMut(&T) -> Option<T>,
{
type Item = T;
pub use self::successors::{successors, Successors};
#[inline]
fn next(&mut self) -> Option<Self::Item> {
let item = self.next.take()?;
self.next = (self.succ)(&item);
Some(item)
}
#[inline]
fn size_hint(&self) -> (usize, Option<usize>) {
if self.next.is_some() { (1, None) } else { (0, Some(0)) }
}
}
#[stable(feature = "iter_successors", since = "1.34.0")]
impl<T, F> FusedIterator for Successors<T, F> where F: FnMut(&T) -> Option<T> {}
#[stable(feature = "iter_successors", since = "1.34.0")]
impl<T: fmt::Debug, F> fmt::Debug for Successors<T, F> {
fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
f.debug_struct("Successors").field("next", &self.next).finish()
}
}
#[stable(feature = "iter_once_with", since = "1.43.0")]
pub use self::once_with::{once_with, OnceWith};

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use crate::fmt;
use crate::iter::{FusedIterator, TrustedLen};
use crate::marker;
/// Creates an iterator that yields nothing.
///
/// # Examples
///
/// Basic usage:
///
/// ```
/// use std::iter;
///
/// // this could have been an iterator over i32, but alas, it's just not.
/// let mut nope = iter::empty::<i32>();
///
/// assert_eq!(None, nope.next());
/// ```
#[stable(feature = "iter_empty", since = "1.2.0")]
#[rustc_const_stable(feature = "const_iter_empty", since = "1.32.0")]
pub const fn empty<T>() -> Empty<T> {
Empty(marker::PhantomData)
}
/// An iterator that yields nothing.
///
/// This `struct` is created by the [`empty()`] function. See its documentation for more.
#[stable(feature = "iter_empty", since = "1.2.0")]
pub struct Empty<T>(marker::PhantomData<T>);
#[stable(feature = "iter_empty_send_sync", since = "1.42.0")]
unsafe impl<T> Send for Empty<T> {}
#[stable(feature = "iter_empty_send_sync", since = "1.42.0")]
unsafe impl<T> Sync for Empty<T> {}
#[stable(feature = "core_impl_debug", since = "1.9.0")]
impl<T> fmt::Debug for Empty<T> {
fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
f.pad("Empty")
}
}
#[stable(feature = "iter_empty", since = "1.2.0")]
impl<T> Iterator for Empty<T> {
type Item = T;
fn next(&mut self) -> Option<T> {
None
}
fn size_hint(&self) -> (usize, Option<usize>) {
(0, Some(0))
}
}
#[stable(feature = "iter_empty", since = "1.2.0")]
impl<T> DoubleEndedIterator for Empty<T> {
fn next_back(&mut self) -> Option<T> {
None
}
}
#[stable(feature = "iter_empty", since = "1.2.0")]
impl<T> ExactSizeIterator for Empty<T> {
fn len(&self) -> usize {
0
}
}
#[unstable(feature = "trusted_len", issue = "37572")]
unsafe impl<T> TrustedLen for Empty<T> {}
#[stable(feature = "fused", since = "1.26.0")]
impl<T> FusedIterator for Empty<T> {}
// not #[derive] because that adds a Clone bound on T,
// which isn't necessary.
#[stable(feature = "iter_empty", since = "1.2.0")]
impl<T> Clone for Empty<T> {
fn clone(&self) -> Empty<T> {
Empty(marker::PhantomData)
}
}
// not #[derive] because that adds a Default bound on T,
// which isn't necessary.
#[stable(feature = "iter_empty", since = "1.2.0")]
impl<T> Default for Empty<T> {
fn default() -> Empty<T> {
Empty(marker::PhantomData)
}
}

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use crate::fmt;
/// Creates a new iterator where each iteration calls the provided closure
/// `F: FnMut() -> Option<T>`.
///
/// This allows creating a custom iterator with any behavior
/// without using the more verbose syntax of creating a dedicated type
/// and implementing the [`Iterator`] trait for it.
///
/// Note that the `FromFn` iterator doesn’t make assumptions about the behavior of the closure,
/// and therefore conservatively does not implement [`FusedIterator`],
/// or override [`Iterator::size_hint()`] from its default `(0, None)`.
///
/// The closure can use captures and its environment to track state across iterations. Depending on
/// how the iterator is used, this may require specifying the [`move`] keyword on the closure.
///
/// [`move`]: ../../std/keyword.move.html
/// [`FusedIterator`]: crate::iter::FusedIterator
///
/// # Examples
///
/// Let’s re-implement the counter iterator from [module-level documentation]:
///
/// [module-level documentation]: crate::iter
///
/// ```
/// let mut count = 0;
/// let counter = std::iter::from_fn(move || {
/// // Increment our count. This is why we started at zero.
/// count += 1;
///
/// // Check to see if we've finished counting or not.
/// if count < 6 {
/// Some(count)
/// } else {
/// None
/// }
/// });
/// assert_eq!(counter.collect::<Vec<_>>(), &[1, 2, 3, 4, 5]);
/// ```
#[inline]
#[stable(feature = "iter_from_fn", since = "1.34.0")]
pub fn from_fn<T, F>(f: F) -> FromFn<F>
where
F: FnMut() -> Option<T>,
{
FromFn(f)
}
/// An iterator where each iteration calls the provided closure `F: FnMut() -> Option<T>`.
///
/// This `struct` is created by the [`iter::from_fn()`] function.
/// See its documentation for more.
///
/// [`iter::from_fn()`]: from_fn
#[derive(Clone)]
#[stable(feature = "iter_from_fn", since = "1.34.0")]
pub struct FromFn<F>(F);
#[stable(feature = "iter_from_fn", since = "1.34.0")]
impl<T, F> Iterator for FromFn<F>
where
F: FnMut() -> Option<T>,
{
type Item = T;
#[inline]
fn next(&mut self) -> Option<Self::Item> {
(self.0)()
}
}
#[stable(feature = "iter_from_fn", since = "1.34.0")]
impl<F> fmt::Debug for FromFn<F> {
fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
f.debug_struct("FromFn").finish()
}
}

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use crate::iter::{FusedIterator, TrustedLen};
/// Creates an iterator that yields an element exactly once.
///
/// This is commonly used to adapt a single value into a [`chain()`] of other
/// kinds of iteration. Maybe you have an iterator that covers almost
/// everything, but you need an extra special case. Maybe you have a function
/// which works on iterators, but you only need to process one value.
///
/// [`chain()`]: Iterator::chain
///
/// # Examples
///
/// Basic usage:
///
/// ```
/// use std::iter;
///
/// // one is the loneliest number
/// let mut one = iter::once(1);
///
/// assert_eq!(Some(1), one.next());
///
/// // just one, that's all we get
/// assert_eq!(None, one.next());
/// ```
///
/// Chaining together with another iterator. Let's say that we want to iterate
/// over each file of the `.foo` directory, but also a configuration file,
/// `.foorc`:
///
/// ```no_run
/// use std::iter;
/// use std::fs;
/// use std::path::PathBuf;
///
/// let dirs = fs::read_dir(".foo").unwrap();
///
/// // we need to convert from an iterator of DirEntry-s to an iterator of
/// // PathBufs, so we use map
/// let dirs = dirs.map(|file| file.unwrap().path());
///
/// // now, our iterator just for our config file
/// let config = iter::once(PathBuf::from(".foorc"));
///
/// // chain the two iterators together into one big iterator
/// let files = dirs.chain(config);
///
/// // this will give us all of the files in .foo as well as .foorc
/// for f in files {
/// println!("{:?}", f);
/// }
/// ```
#[stable(feature = "iter_once", since = "1.2.0")]
pub fn once<T>(value: T) -> Once<T> {
Once { inner: Some(value).into_iter() }
}
/// An iterator that yields an element exactly once.
///
/// This `struct` is created by the [`once()`] function. See its documentation for more.
#[derive(Clone, Debug)]
#[stable(feature = "iter_once", since = "1.2.0")]
pub struct Once<T> {
inner: crate::option::IntoIter<T>,
}
#[stable(feature = "iter_once", since = "1.2.0")]
impl<T> Iterator for Once<T> {
type Item = T;
fn next(&mut self) -> Option<T> {
self.inner.next()
}
fn size_hint(&self) -> (usize, Option<usize>) {
self.inner.size_hint()
}
}
#[stable(feature = "iter_once", since = "1.2.0")]
impl<T> DoubleEndedIterator for Once<T> {
fn next_back(&mut self) -> Option<T> {
self.inner.next_back()
}
}
#[stable(feature = "iter_once", since = "1.2.0")]
impl<T> ExactSizeIterator for Once<T> {
fn len(&self) -> usize {
self.inner.len()
}
}
#[unstable(feature = "trusted_len", issue = "37572")]
unsafe impl<T> TrustedLen for Once<T> {}
#[stable(feature = "fused", since = "1.26.0")]
impl<T> FusedIterator for Once<T> {}

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use crate::iter::{FusedIterator, TrustedLen};
/// Creates an iterator that lazily generates a value exactly once by invoking
/// the provided closure.
///
/// This is commonly used to adapt a single value generator into a [`chain()`] of
/// other kinds of iteration. Maybe you have an iterator that covers almost
/// everything, but you need an extra special case. Maybe you have a function
/// which works on iterators, but you only need to process one value.
///
/// Unlike [`once()`], this function will lazily generate the value on request.
///
/// [`chain()`]: Iterator::chain
/// [`once()`]: crate::iter::once
///
/// # Examples
///
/// Basic usage:
///
/// ```
/// use std::iter;
///
/// // one is the loneliest number
/// let mut one = iter::once_with(|| 1);
///
/// assert_eq!(Some(1), one.next());
///
/// // just one, that's all we get
/// assert_eq!(None, one.next());
/// ```
///
/// Chaining together with another iterator. Let's say that we want to iterate
/// over each file of the `.foo` directory, but also a configuration file,
/// `.foorc`:
///
/// ```no_run
/// use std::iter;
/// use std::fs;
/// use std::path::PathBuf;
///
/// let dirs = fs::read_dir(".foo").unwrap();
///
/// // we need to convert from an iterator of DirEntry-s to an iterator of
/// // PathBufs, so we use map
/// let dirs = dirs.map(|file| file.unwrap().path());
///
/// // now, our iterator just for our config file
/// let config = iter::once_with(|| PathBuf::from(".foorc"));
///
/// // chain the two iterators together into one big iterator
/// let files = dirs.chain(config);
///
/// // this will give us all of the files in .foo as well as .foorc
/// for f in files {
/// println!("{:?}", f);
/// }
/// ```
#[inline]
#[stable(feature = "iter_once_with", since = "1.43.0")]
pub fn once_with<A, F: FnOnce() -> A>(gen: F) -> OnceWith<F> {
OnceWith { gen: Some(gen) }
}
/// An iterator that yields a single element of type `A` by
/// applying the provided closure `F: FnOnce() -> A`.
///
/// This `struct` is created by the [`once_with()`] function.
/// See its documentation for more.
#[derive(Clone, Debug)]
#[stable(feature = "iter_once_with", since = "1.43.0")]
pub struct OnceWith<F> {
gen: Option<F>,
}
#[stable(feature = "iter_once_with", since = "1.43.0")]
impl<A, F: FnOnce() -> A> Iterator for OnceWith<F> {
type Item = A;
#[inline]
fn next(&mut self) -> Option<A> {
let f = self.gen.take()?;
Some(f())
}
#[inline]
fn size_hint(&self) -> (usize, Option<usize>) {
self.gen.iter().size_hint()
}
}
#[stable(feature = "iter_once_with", since = "1.43.0")]
impl<A, F: FnOnce() -> A> DoubleEndedIterator for OnceWith<F> {
fn next_back(&mut self) -> Option<A> {
self.next()
}
}
#[stable(feature = "iter_once_with", since = "1.43.0")]
impl<A, F: FnOnce() -> A> ExactSizeIterator for OnceWith<F> {
fn len(&self) -> usize {
self.gen.iter().len()
}
}
#[stable(feature = "iter_once_with", since = "1.43.0")]
impl<A, F: FnOnce() -> A> FusedIterator for OnceWith<F> {}
#[stable(feature = "iter_once_with", since = "1.43.0")]
unsafe impl<A, F: FnOnce() -> A> TrustedLen for OnceWith<F> {}

93
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@ -0,0 +1,93 @@
use crate::iter::{FusedIterator, TrustedLen};
/// Creates a new iterator that endlessly repeats a single element.
///
/// The `repeat()` function repeats a single value over and over again.
///
/// Infinite iterators like `repeat()` are often used with adapters like
/// [`Iterator::take()`], in order to make them finite.
///
/// If the element type of the iterator you need does not implement `Clone`,
/// or if you do not want to keep the repeated element in memory, you can
/// instead use the [`repeat_with()`] function.
///
/// [`repeat_with()`]: crate::iter::repeat_with
///
/// # Examples
///
/// Basic usage:
///
/// ```
/// use std::iter;
///
/// // the number four 4ever:
/// let mut fours = iter::repeat(4);
///
/// assert_eq!(Some(4), fours.next());
/// assert_eq!(Some(4), fours.next());
/// assert_eq!(Some(4), fours.next());
/// assert_eq!(Some(4), fours.next());
/// assert_eq!(Some(4), fours.next());
///
/// // yup, still four
/// assert_eq!(Some(4), fours.next());
/// ```
///
/// Going finite with [`Iterator::take()`]:
///
/// ```
/// use std::iter;
///
/// // that last example was too many fours. Let's only have four fours.
/// let mut four_fours = iter::repeat(4).take(4);
///
/// assert_eq!(Some(4), four_fours.next());
/// assert_eq!(Some(4), four_fours.next());
/// assert_eq!(Some(4), four_fours.next());
/// assert_eq!(Some(4), four_fours.next());
///
/// // ... and now we're done
/// assert_eq!(None, four_fours.next());
/// ```
#[inline]
#[stable(feature = "rust1", since = "1.0.0")]
pub fn repeat<T: Clone>(elt: T) -> Repeat<T> {
Repeat { element: elt }
}
/// An iterator that repeats an element endlessly.
///
/// This `struct` is created by the [`repeat()`] function. See its documentation for more.
#[derive(Clone, Debug)]
#[stable(feature = "rust1", since = "1.0.0")]
pub struct Repeat<A> {
element: A,
}
#[stable(feature = "rust1", since = "1.0.0")]
impl<A: Clone> Iterator for Repeat<A> {
type Item = A;
#[inline]
fn next(&mut self) -> Option<A> {
Some(self.element.clone())
}
#[inline]
fn size_hint(&self) -> (usize, Option<usize>) {
(usize::MAX, None)
}
}
#[stable(feature = "rust1", since = "1.0.0")]
impl<A: Clone> DoubleEndedIterator for Repeat<A> {
#[inline]
fn next_back(&mut self) -> Option<A> {
Some(self.element.clone())
}
}
#[stable(feature = "fused", since = "1.26.0")]
impl<A: Clone> FusedIterator for Repeat<A> {}
#[unstable(feature = "trusted_len", issue = "37572")]
unsafe impl<A: Clone> TrustedLen for Repeat<A> {}

98
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use crate::iter::{FusedIterator, TrustedLen};
/// Creates a new iterator that repeats elements of type `A` endlessly by
/// applying the provided closure, the repeater, `F: FnMut() -> A`.
///
/// The `repeat_with()` function calls the repeater over and over again.
///
/// Infinite iterators like `repeat_with()` are often used with adapters like
/// [`Iterator::take()`], in order to make them finite.
///
/// If the element type of the iterator you need implements [`Clone`], and
/// it is OK to keep the source element in memory, you should instead use
/// the [`repeat()`] function.
///
/// An iterator produced by `repeat_with()` is not a [`DoubleEndedIterator`].
/// If you need `repeat_with()` to return a [`DoubleEndedIterator`],
/// please open a GitHub issue explaining your use case.
///
/// [`repeat()`]: crate::iter::repeat
/// [`DoubleEndedIterator`]: crate::iter::DoubleEndedIterator
///
/// # Examples
///
/// Basic usage:
///
/// ```
/// use std::iter;
///
/// // let's assume we have some value of a type that is not `Clone`
/// // or which don't want to have in memory just yet because it is expensive:
/// #[derive(PartialEq, Debug)]
/// struct Expensive;
///
/// // a particular value forever:
/// let mut things = iter::repeat_with(|| Expensive);
///
/// assert_eq!(Some(Expensive), things.next());
/// assert_eq!(Some(Expensive), things.next());
/// assert_eq!(Some(Expensive), things.next());
/// assert_eq!(Some(Expensive), things.next());
/// assert_eq!(Some(Expensive), things.next());
/// ```
///
/// Using mutation and going finite:
///
/// ```rust
/// use std::iter;
///
/// // From the zeroth to the third power of two:
/// let mut curr = 1;
/// let mut pow2 = iter::repeat_with(|| { let tmp = curr; curr *= 2; tmp })
/// .take(4);
///
/// assert_eq!(Some(1), pow2.next());
/// assert_eq!(Some(2), pow2.next());
/// assert_eq!(Some(4), pow2.next());
/// assert_eq!(Some(8), pow2.next());
///
/// // ... and now we're done
/// assert_eq!(None, pow2.next());
/// ```
#[inline]
#[stable(feature = "iterator_repeat_with", since = "1.28.0")]
pub fn repeat_with<A, F: FnMut() -> A>(repeater: F) -> RepeatWith<F> {
RepeatWith { repeater }
}
/// An iterator that repeats elements of type `A` endlessly by
/// applying the provided closure `F: FnMut() -> A`.
///
/// This `struct` is created by the [`repeat_with()`] function.
/// See its documentation for more.
#[derive(Copy, Clone, Debug)]
#[stable(feature = "iterator_repeat_with", since = "1.28.0")]
pub struct RepeatWith<F> {
repeater: F,
}
#[stable(feature = "iterator_repeat_with", since = "1.28.0")]
impl<A, F: FnMut() -> A> Iterator for RepeatWith<F> {
type Item = A;
#[inline]
fn next(&mut self) -> Option<A> {
Some((self.repeater)())
}
#[inline]
fn size_hint(&self) -> (usize, Option<usize>) {
(usize::MAX, None)
}
}
#[stable(feature = "iterator_repeat_with", since = "1.28.0")]
impl<A, F: FnMut() -> A> FusedIterator for RepeatWith<F> {}
#[unstable(feature = "trusted_len", issue = "37572")]
unsafe impl<A, F: FnMut() -> A> TrustedLen for RepeatWith<F> {}

66
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use crate::{fmt, iter::FusedIterator};
/// Creates a new iterator where each successive item is computed based on the preceding one.
///
/// The iterator starts with the given first item (if any)
/// and calls the given `FnMut(&T) -> Option<T>` closure to compute each item’s successor.
///
/// ```
/// use std::iter::successors;
///
/// let powers_of_10 = successors(Some(1_u16), |n| n.checked_mul(10));
/// assert_eq!(powers_of_10.collect::<Vec<_>>(), &[1, 10, 100, 1_000, 10_000]);
/// ```
#[stable(feature = "iter_successors", since = "1.34.0")]
pub fn successors<T, F>(first: Option<T>, succ: F) -> Successors<T, F>
where
F: FnMut(&T) -> Option<T>,
{
// If this function returned `impl Iterator<Item=T>`
// it could be based on `unfold` and not need a dedicated type.
// However having a named `Successors<T, F>` type allows it to be `Clone` when `T` and `F` are.
Successors { next: first, succ }
}
/// An new iterator where each successive item is computed based on the preceding one.
///
/// This `struct` is created by the [`iter::successors()`] function.
/// See its documentation for more.
///
/// [`iter::successors()`]: successors
#[derive(Clone)]
#[stable(feature = "iter_successors", since = "1.34.0")]
pub struct Successors<T, F> {
next: Option<T>,
succ: F,
}
#[stable(feature = "iter_successors", since = "1.34.0")]
impl<T, F> Iterator for Successors<T, F>
where
F: FnMut(&T) -> Option<T>,
{
type Item = T;
#[inline]
fn next(&mut self) -> Option<Self::Item> {
let item = self.next.take()?;
self.next = (self.succ)(&item);
Some(item)
}
#[inline]
fn size_hint(&self) -> (usize, Option<usize>) {
if self.next.is_some() { (1, None) } else { (0, Some(0)) }
}
}
#[stable(feature = "iter_successors", since = "1.34.0")]
impl<T, F> FusedIterator for Successors<T, F> where F: FnMut(&T) -> Option<T> {}
#[stable(feature = "iter_successors", since = "1.34.0")]
impl<T: fmt::Debug, F> fmt::Debug for Successors<T, F> {
fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
f.debug_struct("Successors").field("next", &self.next).finish()
}
}

6
src/test/ui/issues/issue-31173.stderr
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@ -13,11 +13,13 @@ error[E0599]: no method named `collect` found for struct `Cloned<TakeWhile<&mut
LL | .collect();
| ^^^^^^^ method not found in `Cloned<TakeWhile<&mut std::vec::IntoIter<u8>, [closure@$DIR/issue-31173.rs:6:39: 9:6]>>`
|
::: $SRC_DIR/core/src/iter/adapters/mod.rs:LL:COL
::: $SRC_DIR/core/src/iter/adapters/cloned.rs:LL:COL
|
LL | pub struct Cloned<I> {
| -------------------- doesn't satisfy `_: Iterator`
...
|
::: $SRC_DIR/core/src/iter/adapters/take_while.rs:LL:COL
|
LL | pub struct TakeWhile<I, P> {
| -------------------------- doesn't satisfy `<_ as Iterator>::Item = &_`
|

2
src/test/ui/mismatched_types/issue-36053-2.stderr
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@ -15,7 +15,7 @@ LL | once::<&str>("str").fuse().filter(|a: &str| true).count();
| doesn't satisfy `<_ as FnOnce<(&&str,)>>::Output = bool`
| doesn't satisfy `_: FnMut<(&&str,)>`
|
::: $SRC_DIR/core/src/iter/adapters/mod.rs:LL:COL
::: $SRC_DIR/core/src/iter/adapters/filter.rs:LL:COL
|
LL | pub struct Filter<I, P> {
| ----------------------- doesn't satisfy `_: Iterator`