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Specialize Vec::clone_from for Copy types

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This should improve performance and reduce code size.

This also improves `clone_from` for `String`, `OsString` and `PathBuf`.
This commit is contained in:
Benoît du Garreau 2021-08-10 11:45:52 +02:00
parent ae90dcf020
commit 361398009b
1 changed files with 27 additions and 10 deletions
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37
library/alloc/src/vec/mod.rs
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@ -2378,6 +2378,32 @@ impl<T, A: Allocator> ops::DerefMut for Vec<T, A> {
}
}
trait SpecCloneFrom {
fn clone_from(this: &mut Self, other: &Self);
}
impl<T: Clone, A: Allocator> SpecCloneFrom for Vec<T, A> {
default fn clone_from(this: &mut Self, other: &Self) {
// drop anything that will not be overwritten
this.truncate(other.len());
// self.len <= other.len due to the truncate above, so the
// slices here are always in-bounds.
let (init, tail) = other.split_at(this.len());
// reuse the contained values' allocations/resources.
this.clone_from_slice(init);
this.extend_from_slice(tail);
}
}
impl<T: Copy, A: Allocator> SpecCloneFrom for Vec<T, A> {
fn clone_from(this: &mut Self, other: &Self) {
this.clear();
this.extend_from_slice(other);
}
}
#[cfg(not(no_global_oom_handling))]
#[stable(feature = "rust1", since = "1.0.0")]
impl<T: Clone, A: Allocator + Clone> Clone for Vec<T, A> {
@ -2398,16 +2424,7 @@ impl<T: Clone, A: Allocator + Clone> Clone for Vec<T, A> {
}
fn clone_from(&mut self, other: &Self) {
// drop anything that will not be overwritten
self.truncate(other.len());
// self.len <= other.len due to the truncate above, so the
// slices here are always in-bounds.
let (init, tail) = other.split_at(self.len());
// reuse the contained values' allocations/resources.
self.clone_from_slice(init);
self.extend_from_slice(tail);
SpecCloneFrom::clone_from(self, other)
}
}