Match VecDeque::extend to Vec::extend_desugared
#66341
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r? @Kimundi (rust_highfive has picked a reviewer for you, use r? to override) |
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Ping from Triage: Any update? @hellow554 @Kimundi? |
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r? @SimonSapin |
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Ping from triage @SimonSapin any updates on this? Thanks. |
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Sorry. I’m not familiar enough with internals of r? @Dylan-DPC |
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r? @dtolnay |
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r? @Amanieu |
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@bors r+ |
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📌 Commit 164d1a2 has been approved by |
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⌛ Testing commit 164d1a2 with merge 6c6235d30d605fa38b55d059a8c57b3e1149885b... |
Match `VecDeque::extend` to `Vec::extend_desugared` Currently, `VecDeque::extend` [does not reserve at all](rust-lang#65069 (comment)). This implementation still runs a check every iteration of the loop, but should reallocate at most once for the common cases where the `size_hint` lower bound is exact. Further optimizations in the future could improve this for some common cases, but given the complexity of the `Vec::extend` implementation it's not immediately clear that this would be worthwhile.
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@bors retry rolled up. |
Rollup of 6 pull requests Successful merges: - #66341 (Match `VecDeque::extend` to `Vec::extend_desugared`) - #67243 (LinkedList: drop remaining items when drop panics) - #67247 (Don't suggest wrong snippet in closure) - #67250 (Remove the `DelimSpan` from `NamedMatch::MatchedSeq`.) - #67251 (Require `allow_internal_unstable` for stable min_const_fn using unsta…) - #67269 (parser: recover on `&'lifetime mut? $pat`.) Failed merges: r? @ghost
| // } | ||
| let mut iter = iter.into_iter(); | ||
| while let Some(element) = iter.next() { | ||
| if self.len() == self.capacity() { |
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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(...);
}There was a problem hiding this comment.
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
Currently,
VecDeque::extenddoes not reserve at all. This implementation still runs a check every iteration of the loop, but should reallocate at most once for the common cases where thesize_hintlower bound is exact. Further optimizations in the future could improve this for some common cases, but given the complexity of theVec::extendimplementation it's not immediately clear that this would be worthwhile.