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use From specializations on extend if extended Vec is empty

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this enables in-place iteration and allocation reuse in additional cases
This commit is contained in:
The8472 2019-11-21 13:24:48 +01:00
parent a596ff36b5
commit 582fbb1d62
1 changed files with 25 additions and 3 deletions
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28
library/alloc/src/vec.rs
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@ -2080,7 +2080,16 @@ impl<'a, T> IntoIterator for &'a mut Vec<T> {
impl<T> Extend<T> for Vec<T> { impl<T> Extend<T> for Vec<T> {
#[inline] #[inline]
fn extend<I: IntoIterator<Item = T>>(&mut self, iter: I) { fn extend<I: IntoIterator<Item = T>>(&mut self, iter: I) {
<Self as SpecExtend<T, I::IntoIter>>::spec_extend(self, iter.into_iter()) if self.capacity() > 0 {
<Self as SpecExtend<T, I::IntoIter>>::spec_extend(self, iter.into_iter())
} else {
// if self has no allocation then use the more powerful from_iter specializations
let other = SpecFrom::from_iter(iter.into_iter());
// replace self, don't run drop since self was empty
unsafe {
ptr::write(self, other);
}
}
} }
#[inline] #[inline]
@ -2121,6 +2130,8 @@ where
vector vector
} }
}; };
// must delegate to spec_extend() since extend() itself delegates
// to spec_from for empty Vecs
<Vec<T> as SpecExtend<T, I>>::spec_extend(&mut vector, iterator); <Vec<T> as SpecExtend<T, I>>::spec_extend(&mut vector, iterator);
vector vector
} }
@ -2230,7 +2241,9 @@ impl<T> SpecFrom<T, IntoIter<T>> for Vec<T> {
} }
let mut vec = Vec::new(); let mut vec = Vec::new();
vec.extend(iterator); // must delegate to spec_extend() since extend() itself delegates
// to spec_from for empty Vecs
vec.spec_extend(iterator);
vec vec
} }
} }
@ -2475,7 +2488,16 @@ impl<T> Vec<T> {
#[stable(feature = "extend_ref", since = "1.2.0")] #[stable(feature = "extend_ref", since = "1.2.0")]
impl<'a, T: 'a + Copy> Extend<&'a T> for Vec<T> { impl<'a, T: 'a + Copy> Extend<&'a T> for Vec<T> {
fn extend<I: IntoIterator<Item = &'a T>>(&mut self, iter: I) { fn extend<I: IntoIterator<Item = &'a T>>(&mut self, iter: I) {
self.spec_extend(iter.into_iter()) if self.capacity() > 0 {
self.spec_extend(iter.into_iter())
} else {
// if self has no allocation then use the more powerful from_iter specializations
let other = SpecFrom::from_iter(iter.into_iter());
// replace self, don't run drop since self was empty
unsafe {
ptr::write(self, other);
}
}
} }
#[inline] #[inline]