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| author | Mazdak Farrokhzad <twingoow@gmail.com> | 2019-06-20 23:20:21 +0200 |
|---|---|---|
| committer | Mazdak Farrokhzad <twingoow@gmail.com> | 2019-06-20 23:20:21 +0200 |
| commit | 6b8417b55c59f3412e97131fd1f99e34bdd8f5d2 (patch) | |
| tree | 7fa792991dc7fee7dc6809f5ad02af67983ab214 | |
| parent | 85978d028ad6edb1530c494682c05b46f26900f6 (diff) | |
| download | rust-6b8417b55c59f3412e97131fd1f99e34bdd8f5d2.tar.gz rust-6b8417b55c59f3412e97131fd1f99e34bdd8f5d2.zip | |
shared_from_iter: Clarify slice::Iter specialization impl.
| -rw-r--r-- | src/liballoc/rc.rs | 10 | ||||
| -rw-r--r-- | src/liballoc/sync.rs | 10 |
2 files changed, 16 insertions, 4 deletions
diff --git a/src/liballoc/rc.rs b/src/liballoc/rc.rs index a222dbc93a8..9b653fe2d75 100644 --- a/src/liballoc/rc.rs +++ b/src/liballoc/rc.rs @@ -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() } } diff --git a/src/liballoc/sync.rs b/src/liballoc/sync.rs index f5110905a11..672481ca0de 100644 --- a/src/liballoc/sync.rs +++ b/src/liballoc/sync.rs @@ -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() } } |