From b96b9b409309bc84807f37643c90f76de4bfb0d5 Mon Sep 17 00:00:00 2001 From: Scott McMurray Date: Fri, 26 Nov 2021 23:09:34 -0800 Subject: [PATCH] Make array::{try_from_fn, try_map} and Iterator::try_find generic over Try Fixes 85115 This only updates unstable functions. `array::try_map` didn't actually exist before, despite the tracking issue 79711 still being open from the old PR 79713. --- library/core/src/array/mod.rs | 116 ++++++++++++++++------- library/core/src/iter/traits/iterator.rs | 44 ++++++--- library/core/src/ops/control_flow.rs | 5 + library/core/src/ops/mod.rs | 5 + library/core/src/ops/try_trait.rs | 58 ++++++++++++ library/core/src/option.rs | 5 + library/core/src/result.rs | 5 + library/core/tests/array.rs | 2 +- 8 files changed, 195 insertions(+), 45 deletions(-) diff --git a/library/core/src/array/mod.rs b/library/core/src/array/mod.rs index 39ccbaaaf7b..d635829151e 100644 --- a/library/core/src/array/mod.rs +++ b/library/core/src/array/mod.rs @@ -11,7 +11,9 @@ use crate::fmt; use crate::hash::{self, Hash}; use crate::iter::TrustedLen; use crate::mem::{self, MaybeUninit}; -use crate::ops::{Index, IndexMut}; +use crate::ops::{ + ChangeOutputType, ControlFlow, FromResidual, Index, IndexMut, NeverShortCircuit, Residual, Try, +}; use crate::slice::{Iter, IterMut}; mod equality; @@ -49,9 +51,13 @@ where } /// Creates an array `[T; N]` where each fallible array element `T` is returned by the `cb` call. -/// Unlike `core::array::from_fn`, where the element creation can't fail, this version will return an error +/// Unlike [`from_fn`], where the element creation can't fail, this version will return an error /// if any element creation was unsuccessful. /// +/// The return type of this function depends on the return type of the closure. +/// If you return `Result` from the closure, you'll get a `Result<[T; N]; E>`. +/// If you return `Option` from the closure, you'll get an `Option<[T; N]>`. +/// /// # Arguments /// /// * `cb`: Callback where the passed argument is the current array index. @@ -60,27 +66,32 @@ where /// /// ```rust /// #![feature(array_from_fn)] +/// # // Apparently these doc tests are still on edition2018 +/// # use std::convert::TryInto; /// -/// #[derive(Debug, PartialEq)] -/// enum SomeError { -/// Foo, -/// } -/// -/// let array = core::array::try_from_fn(|i| Ok::<_, SomeError>(i)); +/// let array: Result<[u8; 5], _> = std::array::try_from_fn(|i| i.try_into()); /// assert_eq!(array, Ok([0, 1, 2, 3, 4])); /// -/// let another_array = core::array::try_from_fn::(|_| Err(SomeError::Foo)); -/// assert_eq!(another_array, Err(SomeError::Foo)); +/// let array: Result<[i8; 200], _> = std::array::try_from_fn(|i| i.try_into()); +/// assert!(array.is_err()); +/// +/// let array: Option<[_; 4]> = std::array::try_from_fn(|i| i.checked_add(100)); +/// assert_eq!(array, Some([100, 101, 102, 103])); +/// +/// let array: Option<[_; 4]> = std::array::try_from_fn(|i| i.checked_sub(100)); +/// assert_eq!(array, None); /// ``` #[inline] #[unstable(feature = "array_from_fn", issue = "89379")] -pub fn try_from_fn(cb: F) -> Result<[T; N], E> +pub fn try_from_fn(cb: F) -> ChangeOutputType where - F: FnMut(usize) -> Result, + F: FnMut(usize) -> R, + R: Try, + R::Residual: Residual<[R::Output; N]>, { // SAFETY: we know for certain that this iterator will yield exactly `N` // items. - unsafe { collect_into_array_rslt_unchecked(&mut (0..N).map(cb)) } + unsafe { try_collect_into_array_unchecked(&mut (0..N).map(cb)) } } /// Converts a reference to `T` into a reference to an array of length 1 (without copying). @@ -444,6 +455,45 @@ impl [T; N] { unsafe { collect_into_array_unchecked(&mut IntoIterator::into_iter(self).map(f)) } } + /// A fallible function `f` applied to each element on array `self` in order to + /// return an array the same size as `self` or the first error encountered. + /// + /// The return type of this function depends on the return type of the closure. + /// If you return `Result` from the closure, you'll get a `Result<[T; N]; E>`. + /// If you return `Option` from the closure, you'll get an `Option<[T; N]>`. + /// + /// # Examples + /// + /// ``` + /// #![feature(array_try_map)] + /// let a = ["1", "2", "3"]; + /// let b = a.try_map(|v| v.parse::()).unwrap().map(|v| v + 1); + /// assert_eq!(b, [2, 3, 4]); + /// + /// let a = ["1", "2a", "3"]; + /// let b = a.try_map(|v| v.parse::()); + /// assert!(b.is_err()); + /// + /// use std::num::NonZeroU32; + /// let z = [1, 2, 0, 3, 4]; + /// assert_eq!(z.try_map(NonZeroU32::new), None); + /// let a = [1, 2, 3]; + /// let b = a.try_map(NonZeroU32::new); + /// let c = b.map(|x| x.map(NonZeroU32::get)); + /// assert_eq!(c, Some(a)); + /// ``` + #[unstable(feature = "array_try_map", issue = "79711")] + pub fn try_map(self, f: F) -> ChangeOutputType + where + F: FnMut(T) -> R, + R: Try, + R::Residual: Residual<[R::Output; N]>, + { + // SAFETY: we know for certain that this iterator will yield exactly `N` + // items. + unsafe { try_collect_into_array_unchecked(&mut IntoIterator::into_iter(self).map(f)) } + } + /// 'Zips up' two arrays into a single array of pairs. /// /// `zip()` returns a new array where every element is a tuple where the @@ -621,42 +671,42 @@ impl [T; N] { /// Pulls `N` items from `iter` and returns them as an array. If the iterator /// yields fewer than `N` items, this function exhibits undefined behavior. /// -/// See [`collect_into_array`] for more information. +/// See [`try_collect_into_array`] for more information. /// /// /// # Safety /// /// It is up to the caller to guarantee that `iter` yields at least `N` items. /// Violating this condition causes undefined behavior. -unsafe fn collect_into_array_rslt_unchecked( - iter: &mut I, -) -> Result<[T; N], E> +unsafe fn try_collect_into_array_unchecked(iter: &mut I) -> R::TryType where // Note: `TrustedLen` here is somewhat of an experiment. This is just an // internal function, so feel free to remove if this bound turns out to be a // bad idea. In that case, remember to also remove the lower bound // `debug_assert!` below! - I: Iterator> + TrustedLen, + I: Iterator + TrustedLen, + I::Item: Try, + R: Residual<[T; N]>, { debug_assert!(N <= iter.size_hint().1.unwrap_or(usize::MAX)); debug_assert!(N <= iter.size_hint().0); // SAFETY: covered by the function contract. - unsafe { collect_into_array(iter).unwrap_unchecked() } + unsafe { try_collect_into_array(iter).unwrap_unchecked() } } -// Infallible version of `collect_into_array_rslt_unchecked`. +// Infallible version of `try_collect_into_array_unchecked`. unsafe fn collect_into_array_unchecked(iter: &mut I) -> [I::Item; N] where I: Iterator + TrustedLen, { - let mut map = iter.map(Ok::<_, Infallible>); + let mut map = iter.map(NeverShortCircuit); // SAFETY: The same safety considerations w.r.t. the iterator length - // apply for `collect_into_array_rslt_unchecked` as for + // apply for `try_collect_into_array_unchecked` as for // `collect_into_array_unchecked` - match unsafe { collect_into_array_rslt_unchecked(&mut map) } { - Ok(array) => array, + match unsafe { try_collect_into_array_unchecked(&mut map) } { + NeverShortCircuit(array) => array, } } @@ -670,13 +720,15 @@ where /// /// If `iter.next()` panicks, all items already yielded by the iterator are /// dropped. -fn collect_into_array(iter: &mut I) -> Option> +fn try_collect_into_array(iter: &mut I) -> Option where - I: Iterator>, + I: Iterator, + I::Item: Try, + R: Residual<[T; N]>, { if N == 0 { // SAFETY: An empty array is always inhabited and has no validity invariants. - return unsafe { Some(Ok(mem::zeroed())) }; + return unsafe { Some(Try::from_output(mem::zeroed())) }; } struct Guard<'a, T, const N: usize> { @@ -701,11 +753,11 @@ where let mut guard = Guard { array_mut: &mut array, initialized: 0 }; while let Some(item_rslt) = iter.next() { - let item = match item_rslt { - Err(err) => { - return Some(Err(err)); + let item = match item_rslt.branch() { + ControlFlow::Break(r) => { + return Some(FromResidual::from_residual(r)); } - Ok(elem) => elem, + ControlFlow::Continue(elem) => elem, }; // SAFETY: `guard.initialized` starts at 0, is increased by one in the @@ -723,7 +775,7 @@ where // SAFETY: the condition above asserts that all elements are // initialized. let out = unsafe { MaybeUninit::array_assume_init(array) }; - return Some(Ok(out)); + return Some(Try::from_output(out)); } } diff --git a/library/core/src/iter/traits/iterator.rs b/library/core/src/iter/traits/iterator.rs index 35ce9400f8f..88e7623eba1 100644 --- a/library/core/src/iter/traits/iterator.rs +++ b/library/core/src/iter/traits/iterator.rs @@ -1,5 +1,5 @@ use crate::cmp::{self, Ordering}; -use crate::ops::{ControlFlow, Try}; +use crate::ops::{ChangeOutputType, ControlFlow, FromResidual, Residual, Try}; use super::super::TrustedRandomAccessNoCoerce; use super::super::{Chain, Cloned, Copied, Cycle, Enumerate, Filter, FilterMap, Fuse}; @@ -2418,6 +2418,10 @@ pub trait Iterator { /// Applies function to the elements of iterator and returns /// the first true result or the first error. /// + /// The return type of this method depends on the return type of the closure. + /// If you return `Result` from the closure, you'll get a `Result; E>`. + /// If you return `Option` from the closure, you'll get an `Option>`. + /// /// # Examples /// /// ``` @@ -2435,32 +2439,48 @@ pub trait Iterator { /// let result = a.iter().try_find(|&&s| is_my_num(s, 5)); /// assert!(result.is_err()); /// ``` + /// + /// This also supports other types which implement `Try`, not just `Result`. + /// ``` + /// #![feature(try_find)] + /// + /// use std::num::NonZeroU32; + /// let a = [3, 5, 7, 4, 9, 0, 11]; + /// let result = a.iter().try_find(|&&x| NonZeroU32::new(x).map(|y| y.is_power_of_two())); + /// assert_eq!(result, Some(Some(&4))); + /// let result = a.iter().take(3).try_find(|&&x| NonZeroU32::new(x).map(|y| y.is_power_of_two())); + /// assert_eq!(result, Some(None)); + /// let result = a.iter().rev().try_find(|&&x| NonZeroU32::new(x).map(|y| y.is_power_of_two())); + /// assert_eq!(result, None); + /// ``` #[inline] #[unstable(feature = "try_find", reason = "new API", issue = "63178")] - fn try_find(&mut self, f: F) -> Result, E> + fn try_find(&mut self, f: F) -> ChangeOutputType> where Self: Sized, F: FnMut(&Self::Item) -> R, R: Try, - // FIXME: This bound is rather strange, but means minimal breakage on nightly. - // See #85115 for the issue tracking a holistic solution for this and try_map. - R: Try>, + R::Residual: Residual>, { #[inline] - fn check(mut f: F) -> impl FnMut((), T) -> ControlFlow> + fn check( + mut f: impl FnMut(&I) -> V, + ) -> impl FnMut((), I) -> ControlFlow where - F: FnMut(&T) -> R, - R: Try, - R: Try>, + V: Try, + R: Residual>, { move |(), x| match f(&x).branch() { ControlFlow::Continue(false) => ControlFlow::CONTINUE, - ControlFlow::Continue(true) => ControlFlow::Break(Ok(x)), - ControlFlow::Break(Err(x)) => ControlFlow::Break(Err(x)), + ControlFlow::Continue(true) => ControlFlow::Break(Try::from_output(Some(x))), + ControlFlow::Break(r) => ControlFlow::Break(FromResidual::from_residual(r)), } } - self.try_fold((), check(f)).break_value().transpose() + match self.try_fold((), check(f)) { + ControlFlow::Break(x) => x, + ControlFlow::Continue(()) => Try::from_output(None), + } } /// Searches for an element in an iterator, returning its index. diff --git a/library/core/src/ops/control_flow.rs b/library/core/src/ops/control_flow.rs index b0c15898a1f..5ee8e377de1 100644 --- a/library/core/src/ops/control_flow.rs +++ b/library/core/src/ops/control_flow.rs @@ -123,6 +123,11 @@ impl ops::FromResidual for ControlFlow { } } +#[unstable(feature = "try_trait_v2_residual", issue = "91285")] +impl ops::Residual for ControlFlow { + type TryType = ControlFlow; +} + impl ControlFlow { /// Returns `true` if this is a `Break` variant. /// diff --git a/library/core/src/ops/mod.rs b/library/core/src/ops/mod.rs index 6c866031370..9d1e7e81b0e 100644 --- a/library/core/src/ops/mod.rs +++ b/library/core/src/ops/mod.rs @@ -187,6 +187,11 @@ pub use self::range::OneSidedRange; #[unstable(feature = "try_trait_v2", issue = "84277")] pub use self::try_trait::{FromResidual, Try}; +#[unstable(feature = "try_trait_v2_residual", issue = "91285")] +pub use self::try_trait::Residual; + +pub(crate) use self::try_trait::{ChangeOutputType, NeverShortCircuit}; + #[unstable(feature = "generator_trait", issue = "43122")] pub use self::generator::{Generator, GeneratorState}; diff --git a/library/core/src/ops/try_trait.rs b/library/core/src/ops/try_trait.rs index 6bdcda775ee..f4f0a589809 100644 --- a/library/core/src/ops/try_trait.rs +++ b/library/core/src/ops/try_trait.rs @@ -338,3 +338,61 @@ pub trait FromResidual::Residual> { #[unstable(feature = "try_trait_v2", issue = "84277")] fn from_residual(residual: R) -> Self; } + +/// Allows retrieving the canonical type implementing [`Try`] that has this type +/// as its residual and allows it to hold an `O` as its output. +/// +/// If you think of the `Try` trait as splitting a type into its [`Try::Output`] +/// and [`Try::Residual`] components, this allows putting them back together. +/// +/// For example, +/// `Result: Try>`, +/// and in the other direction, +/// ` as Residual>::TryType = Result`. +#[unstable(feature = "try_trait_v2_residual", issue = "91285")] +pub trait Residual { + /// The "return" type of this meta-function. + #[unstable(feature = "try_trait_v2_residual", issue = "91285")] + type TryType: Try; +} + +#[unstable(feature = "pub_crate_should_not_need_unstable_attr", issue = "none")] +pub(crate) type ChangeOutputType = <::Residual as Residual>::TryType; + +/// An adapter for implementing non-try methods via the `Try` implementation. +/// +/// Conceptually the same as `Result`, but requiring less work in trait +/// solving and inhabited-ness checking and such, by being an obvious newtype +/// and not having `From` bounds lying around. +/// +/// Not currently planned to be exposed publicly, so just `pub(crate)`. +#[repr(transparent)] +pub(crate) struct NeverShortCircuit(pub T); + +pub(crate) enum NeverShortCircuitResidual {} + +impl Try for NeverShortCircuit { + type Output = T; + type Residual = NeverShortCircuitResidual; + + #[inline] + fn branch(self) -> ControlFlow { + ControlFlow::Continue(self.0) + } + + #[inline] + fn from_output(x: T) -> Self { + NeverShortCircuit(x) + } +} + +impl FromResidual for NeverShortCircuit { + #[inline] + fn from_residual(never: NeverShortCircuitResidual) -> Self { + match never {} + } +} + +impl Residual for NeverShortCircuitResidual { + type TryType = NeverShortCircuit; +} diff --git a/library/core/src/option.rs b/library/core/src/option.rs index 4eeb5e43943..4e11162f8c2 100644 --- a/library/core/src/option.rs +++ b/library/core/src/option.rs @@ -2088,6 +2088,11 @@ impl const ops::FromResidual for Option { } } +#[unstable(feature = "try_trait_v2_residual", issue = "91285")] +impl ops::Residual for Option { + type TryType = Option; +} + impl Option> { /// Converts from `Option>` to `Option`. /// diff --git a/library/core/src/result.rs b/library/core/src/result.rs index a494c089f68..e6b8c8ec338 100644 --- a/library/core/src/result.rs +++ b/library/core/src/result.rs @@ -1959,3 +1959,8 @@ impl> ops::FromResidual> for Res } } } + +#[unstable(feature = "try_trait_v2_residual", issue = "91285")] +impl ops::Residual for Result { + type TryType = Result; +} diff --git a/library/core/tests/array.rs b/library/core/tests/array.rs index 7dc071b7423..43d30d12355 100644 --- a/library/core/tests/array.rs +++ b/library/core/tests/array.rs @@ -377,7 +377,7 @@ fn array_try_from_fn() { let array = core::array::try_from_fn(|i| Ok::<_, SomeError>(i)); assert_eq!(array, Ok([0, 1, 2, 3, 4])); - let another_array = core::array::try_from_fn::(|_| Err(SomeError::Foo)); + let another_array = core::array::try_from_fn::<_, Result<(), _>, 2>(|_| Err(SomeError::Foo)); assert_eq!(another_array, Err(SomeError::Foo)); }