Skip to content
New issue

Have a question about this project? Sign up for a free GitHub account to open an issue and contact its maintainers and the community.

Sign up for GitHub

By clicking “Sign up for GitHub”, you agree to our terms of service and privacy statement. We’ll occasionally send you account related emails.

Already on GitHub? Sign in to your account

Jump to bottom

Match VecDeque::extend to Vec::extend_desugared #66341

Merged
merged 1 commit into from
Dec 13, 2019
Merged

Match VecDeque::extend to Vec::extend_desugared #66341

Changes from all commits
Commits
Show all changes
1 commit
Select commit
File filter

Filter by extension

Filter by extension
Conversations
Failed to load comments.
Loading
Jump to
Jump to file
Failed to load files.
Loading
Diff view
Diff view
17 changes: 16 additions & 1 deletion src/liballoc/collections/vec_deque.rs
View file
Open in desktop
Original file line number Diff line number Diff line change
Expand Up @@ -2809,7 +2809,22 @@ impl<'a, T> IntoIterator for &'a mut VecDeque<T> {
#[stable(feature = "rust1", since = "1.0.0")]
impl<A> Extend<A> for VecDeque<A> {
fn extend<T: IntoIterator<Item = A>>(&mut self, iter: T) {
iter.into_iter().for_each(move |elt| self.push_back(elt));
// This function should be the moral equivalent of:
//
// for item in iter.into_iter() {
// self.push_back(item);
// }
let mut iter = iter.into_iter();
while let Some(element) = iter.next() {
if self.len() == self.capacity() {
Copy link
Contributor

Choose a reason for hiding this comment

The reason will be displayed to describe this comment to others. Learn more.

This implementation still runs a check every iteration of the loop

Wouldn't it be possible to move this out of the loop?

let capacity = self.capacity() - self.len();
let (lower, _) = iter.size_hint();
if capacity < lower {
    self.reserve(...);
}

Copy link
Contributor Author

Choose a reason for hiding this comment

The reason will be displayed to describe this comment to others. Learn more.

You could do it for trusted length iterators specifically, but otherwise because it's a lower bound you have to check every time. At some point it could be good to specialize, though

let (lower, _) = iter.size_hint();
self.reserve(lower.saturating_add(1));
}

let head = self.head;
self.head = self.wrap_add(self.head, 1);
unsafe { self.buffer_write(head, element); }
}
}
}

Expand Down