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Implement `Iterator::last` for `vec::IntoIter`
Avoid iterating everything when we have random access to the last element.
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Consistent trait bounds for ExtractIf Debug impls
Closes #137654. Refer to that issue for a table of the **4** different impl signatures we previously had in the standard library for Debug impls of various ExtractIf iterator types.
The one we are standardizing on is the one so far only used by `alloc::collections::linked_list::ExtractIf`, which is _no_ `F: Debug` bound, _no_ `F: FnMut` bound, only `T: Debug` bound.
This PR applies the following signature changes:
```diff
/* alloc::collections::btree_map */
pub struct ExtractIf<'a, K, V, F, A = Global>
where
- F: 'a + FnMut(&K, &mut V) -> bool,
Allocator + Clone,
impl Debug for ExtractIf<'a, K, V, F,
+ A,
>
where
K: Debug,
V: Debug,
- F: FnMut(&K, &mut V) -> bool,
+ A: Allocator + Clone,
```
```diff
/* alloc::collections::btree_set */
pub struct ExtractIf<'a, T, F, A = Global>
where
- T: 'a,
- F: 'a + FnMut(&T) -> bool,
Allocator + Clone,
impl Debug for ExtractIf<'a, T, F, A>
where
T: Debug,
- F: FnMut(&T) -> bool,
A: Allocator + Clone,
```
```diff
/* alloc::collections::linked_list */
impl Debug for ExtractIf<'a, T, F,
+ A,
>
where
T: Debug,
+ A: Allocator,
```
```diff
/* alloc::vec */
impl Debug for ExtractIf<'a, T, F, A>
where
T: Debug,
- F: Debug,
A: Allocator,
- A: Debug,
```
```diff
/* std::collections::hash_map */
pub struct ExtractIf<'a, K, V, F>
where
- F: FnMut(&K, &mut V) -> bool,
impl Debug for ExtractIf<'a, K, V, F>
where
+ K: Debug,
+ V: Debug,
- F: FnMut(&K, &mut V) -> bool,
```
```diff
/* std::collections::hash_set */
pub struct ExtractIf<'a, T, F>
where
- F: FnMut(&T) -> bool,
impl Debug for ExtractIf<'a, T, F>
where
+ T: Debug,
- F: FnMut(&T) -> bool,
```
I have made the following changes to bring these types into better alignment with one another.
- Delete `F: Debug` bounds. These are especially problematic because Rust closures do not come with a Debug impl, rendering the impl useless.
- Delete `A: Debug` bounds. Allocator parameters are unstable for now, but in the future this would become an API commitment that we do not debug-print a representation of the allocator when printing an iterator.
- Delete `F: FnMut` bounds. Requires `hashbrown` PR: https://github.com/rust-lang/hashbrown/pull/616. **API commitment:** we commit to not doing RefCell voodoo inside ExtractIf to have some way for its Debug impl (which takes &self) to call a FnMut closure, if this is even possible.
- Add `T: Debug` bounds (or `K`/`V`), even on Debug impls that do not currently make use of them, but might in the future. **Breaking change.** Must backport into Rust 1.87 (current beta) or do a de-stabilization PR in beta to delay those types by one release.
- Render using `debug_struct` + `finish_non_exhaustive`, instead of `debug_tuple`.
- Do not render the _entire_ underlying collection.
- Show a "peek" field indicating the current position of the iterator.
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Correct `extract_if` sample equivalent.
Tracking issue: https://github.com/rust-lang/rust/issues/43244
Original PR: #133265
The sample code marked as equivalent in the doc comment isn't currently equivalent. Given the same predicate and range, if your vector were `[1, 2, 3, 3, 3, 3, 3, 3, 4, 5, 6]`, then all of the 3s would be removed. `i` is only incremented when an element is dropped, but `range.end` is unchanged, so the items shift down. I got very confused when reading the docs and trying to square this sample code with the explanation of how the function works.
Fortunately, the real `extract_if()` does not have this problem. I've added an `end` variable to align the behavior. I've also taken the opportunity to simplify the predicate, which now just matches odd numbers, and to pad out the vec of numbers to line up the zero-indexed range with the integers in the vec.
r? the8472
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Simpler predicate.
Compare sample code output to that of the library function.
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document capacity for ZST as example
The main text already covers this, although it provides weaker guarantees, but I think an example in the right spot does not hurt. Fixes #80747
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This feature was approved for stabilization in
https://github.com/rust-lang/rust/issues/129041#issuecomment-2508940661
so this change stabilizes it.
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For the tests that make use of internal implementation details, we
include the module to test using #[path] in alloctests now.
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Use `std::mem::{size_of, size_of_val, align_of, align_of_val}` from the
prelude instead of importing or qualifying them.
These functions were added to all preludes in Rust 1.80.
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stabilize extract_if
Tracking issue: #43244
Closes: #43244
FCP completed: https://github.com/rust-lang/rust/issues/43244#issuecomment-2523595704
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Explain how Vec::with_capacity is faithful
This is a revival of https://github.com/rust-lang/rust/pull/99790 building on the prose of `@workingjubilee` and edits of `@jmaargh.` Closes https://github.com/rust-lang/rust/issues/99385.
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rename sub_ptr to offset_from_unsigned
i also made `byte_sub_ptr` `byte_offset_from_unsigned`
fixes #137121
tracking issue #95892
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Co-authored-by: Jubilee <workingjubilee@gmail.com> and jmaargh
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(cherry picked from commit e4840ce59bdddb19394df008c5c26d9c493725f8)
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Stabilize `vec_pop_if`
Tracking issue: #122741
FCP completed in https://github.com/rust-lang/rust/issues/122741#issuecomment-2605116387
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document order of items in iterator from drain
fixes #135710
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Doc difference between extend and extend_from_slice
fixes #97119
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fixes #97119
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fixes 135710
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Add an example for using splice to insert multiple elements efficiently into a vector.
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Fixes #135338
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Asserts the maximum value that can be returned from `Vec::len`
Currently, casting `Vec<i32>` to `Vec<u32>` takes O(1) time:
```rust
// See <https://godbolt.org/z/hxq3hnYKG> for assembly output.
pub fn cast(vec: Vec<i32>) -> Vec<u32> {
vec.into_iter().map(|e| e as _).collect()
}
```
But the generated assembly is not the same as the identity function, which prevents us from casting `Vec<Vec<i32>>` to `Vec<Vec<u32>>` within O(1) time:
```rust
// See <https://godbolt.org/z/7n48bxd9f> for assembly output.
pub fn cast(vec: Vec<Vec<i32>>) -> Vec<Vec<u32>> {
vec.into_iter()
.map(|e| e.into_iter().map(|e| e as _).collect())
.collect()
}
```
This change tries to fix the problem. You can see the comparison here: <https://godbolt.org/z/jdManrKvx>.
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docs: Mention `spare_capacity_mut()` in `Vec::set_len`
I recently went down a small rabbit hole when trying to identify safe use of `Vec::set_len`. The solution was `Vec::spare_capacity_mut`. I think the docs on `Vec::set_len` benefit from mentioning this method.
A possible counter-argument could be that the [clippy lint `uninit_vec`](https://rust-lang.github.io/rust-clippy/master/index.html#/uninit_vec) already nudges people in the right direction. However, I think a working example on `Vec::set_len` is still beneficial.
Happy to hear your thoughts on the matter. :blush:
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since drain-on-drop behavior was removed those bounds
no longer serve a purpose
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In some `Vec` and `VecDeque` examples where elements are i32, examples can seem a bit confusing at first glance if a parameter of the method is an usize.
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Fix missing newlines that rustfmt removed.
fix trailing whitespace
Fix duplicate word.
Reformat panic reasons into a list
remove trailing whitespace 2 electric boogaloo
Change verbe tense.
Integrate suggestions
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Bump boostrap compiler to new beta
Currently failing due to something about the const stability checks and `panic!`. I'm not sure why though since I wasn't able to see any PRs merged in the past few days that would result in a `cfg(bootstrap)` that shouldn't be removed. cc `@RalfJung` #131349
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Add `#[track_caller]` to allocating methods of `Vec` & `VecDeque`
Part 4 in a lengthy saga.
r? `@joshtriplett` because they were the reviewer the last 3 times.
`@bors` rollup=never "[just in case this has perf effects, Vec is hot](https://github.com/rust-lang/rust/pull/79323#issuecomment-731866746)"
This was first attempted in #79323 by `@nvzqz.` It got approval from `@joshtriplett,` but rotted with merge conflicts and got closed.
Then it got picked up by `@Dylan-DPC-zz` in #83359. A benchmark was run[^perf], the results (after a bit of thinking[^thinking]) were deemed ok[^ok], but there was a typo[^typo] and the PR was made from a wrong remote in the first place[^remote], so #83909 was opened instead.
By the time #83909 rolled around, the methods in question had received some optimizations[^optimizations], so another perf run was conducted[^perf2]. The results were ok[^ok2]. There was a suggestion to add regression tests for panic behavior [^tests], but before it could be addressed, the PR fell victim to merge conflicts[^conflicts] and died again[^rip].
3 years have passed, and (from what I can tell) this has not been tried again, so here I am now, reviving this old effort.
Given how much time has passed and the fact that I've also touched `VecDeque` this time, it probably makes sense to
`@bors` try `@rust-timer`
[^perf]: https://github.com/rust-lang/rust/pull/83359#issuecomment-804450095
[^thinking]: https://github.com/rust-lang/rust/pull/83359#issuecomment-805286704
[^ok]: https://github.com/rust-lang/rust/pull/83359#issuecomment-812739031
[^typo]: https://github.com/rust-lang/rust/pull/83359#issuecomment-812750205
[^remote]: https://github.com/rust-lang/rust/pull/83359#issuecomment-814067119
[^optimizations]: https://github.com/rust-lang/rust/pull/83909#issuecomment-813736593
[^perf2]: https://github.com/rust-lang/rust/pull/83909#issuecomment-813825552
[^ok2]: https://github.com/rust-lang/rust/pull/83909#issuecomment-813831341
[^tests]: https://github.com/rust-lang/rust/pull/83909#issuecomment-825788964
[^conflicts]: https://github.com/rust-lang/rust/pull/83909#issuecomment-851173480
[^rip]: https://github.com/rust-lang/rust/pull/83909#issuecomment-873569771
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