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shared_from_iter: Clarify slice::Iter specialization impl.

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This commit is contained in:
Mazdak Farrokhzad 2019-06-20 23:20:21 +02:00
parent 85978d028a
commit 6b8417b55c
2 changed files with 16 additions and 4 deletions
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10
src/liballoc/rc.rs
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@ -1333,8 +1333,14 @@ impl<T, I: iter::TrustedLen<Item = T>> RcFromIter<T, I> for Rc<[T]> {
impl<'a, T: 'a + Clone> RcFromIter<&'a T, slice::Iter<'a, T>> for Rc<[T]> {
fn from_iter(iter: slice::Iter<'a, T>) -> Self {
// Delegate to `impl<T: Clone> From<&[T]> for Rc<[T]>`
// which will use `ptr::copy_nonoverlapping`.
// Delegate to `impl<T: Clone> From<&[T]> for Rc<[T]>`.
//
// In the case that `T: Copy`, we get to use `ptr::copy_nonoverlapping`
// which is even more performant.
//
// In the fall-back case we have `T: Clone`. This is still better
// than the `TrustedLen` implementation as slices have a known length
// and so we get to avoid calling `size_hint` and avoid the branching.
iter.as_slice().into()
}
}

10
src/liballoc/sync.rs
View File

@ -1903,8 +1903,14 @@ impl<T, I: iter::TrustedLen<Item = T>> ArcFromIter<T, I> for Arc<[T]> {
impl<'a, T: 'a + Clone> ArcFromIter<&'a T, slice::Iter<'a, T>> for Arc<[T]> {
fn from_iter(iter: slice::Iter<'a, T>) -> Self {
// Delegate to `impl<T: Clone> From<&[T]> for Arc<[T]>`
// which will use `ptr::copy_nonoverlapping`.
// Delegate to `impl<T: Clone> From<&[T]> for Rc<[T]>`.
//
// In the case that `T: Copy`, we get to use `ptr::copy_nonoverlapping`
// which is even more performant.
//
// In the fall-back case we have `T: Clone`. This is still better
// than the `TrustedLen` implementation as slices have a known length
// and so we get to avoid calling `size_hint` and avoid the branching.
iter.as_slice().into()
}
}