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slice: Add a specialization for clone_into when T is Copy

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The implementation for the ToOwned::clone_into method on [T] is a copy
of the code for vec::clone_from. In 361398009be6 the code for
vec::clone_from gained a specialization for when T is Copy. This commit
copies that specialization over to the clone_into implementation.
This commit is contained in:
Neil Roberts 2023-01-28 14:19:01 +01:00
parent d6f0642827
commit ba80c662f4
1 changed files with 33 additions and 10 deletions
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43
library/alloc/src/slice.rs
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@ -782,6 +782,38 @@ impl<T, A: Allocator> BorrowMut<[T]> for Vec<T, A> {
}
}
// Specializable trait for implementing ToOwned::clone_into. This is
// public in the crate and has the Allocator parameter so that
// vec::clone_from use it too.
#[cfg(not(no_global_oom_handling))]
pub(crate) trait SpecCloneIntoVec<T, A: Allocator> {
fn clone_into(&self, target: &mut Vec<T, A>);
}
#[cfg(not(no_global_oom_handling))]
impl<T: Clone, A: Allocator> SpecCloneIntoVec<T, A> for [T] {
default fn clone_into(&self, target: &mut Vec<T, A>) {
// drop anything in target that will not be overwritten
target.truncate(self.len());
// target.len <= self.len due to the truncate above, so the
// slices here are always in-bounds.
let (init, tail) = self.split_at(target.len());
// reuse the contained values' allocations/resources.
target.clone_from_slice(init);
target.extend_from_slice(tail);
}
}
#[cfg(not(no_global_oom_handling))]
impl<T: Copy, A: Allocator> SpecCloneIntoVec<T, A> for [T] {
fn clone_into(&self, target: &mut Vec<T, A>) {
target.clear();
target.extend_from_slice(self);
}
}
#[cfg(not(no_global_oom_handling))]
#[stable(feature = "rust1", since = "1.0.0")]
impl<T: Clone> ToOwned for [T] {
@ -797,16 +829,7 @@ impl<T: Clone> ToOwned for [T] {
}
fn clone_into(&self, target: &mut Vec<T>) {
// drop anything in target that will not be overwritten
target.truncate(self.len());
// target.len <= self.len due to the truncate above, so the
// slices here are always in-bounds.
let (init, tail) = self.split_at(target.len());
// reuse the contained values' allocations/resources.
target.clone_from_slice(init);
target.extend_from_slice(tail);
SpecCloneIntoVec::clone_into(self, target);
}
}