I found these by grepping for `&[a-z_\.]*\.clone()`, i.e. expressions
like `&a.b.clone()`, which are sometimes unnecessary clones, and also
looking at clones nearby to cases like that.
Add PeekMut::refresh
I'm not sure if this should go through ACP or not. BinaryHeap is not the most critical data structure in the standard library and it would be understandable if maintainer throughput is thus too limited to accept this PR without a proper design phase that ensures the required understanding of consequence over a longer time period.
This aims to improve the useability of heaps for priority-based work queues. In certain scenarios, modifications on the most relevant or critical items are performed until a condition that determines the work items have been sufficiently addressed. For instance the criticality could be a deadline that is relaxed whenever some part of a work item is completed. Such a loop will repeatedly access the most critical item and put it back in a sorted position when it is complete. Crucially, due to the ordering invariant we know that all necessary work was performed when the completed item remains the most critical. Getting this information from the heap position avoids a (potentially more costly) check on the item state itself.
A customized `drop` with boolean result would avoid up to two more comparisons performed in both the last no-op refresh and Drop code but this occurs once in each execution of the above scenario whereas refresh occurs any number of times. Also note that the comparison overhead of Drop is only taken if the element is mutably inspected to determine the end condition, i.e. not when refresh itself is the break condition.
This improves the useability of heaps for priority-based work queues. In
certain scenarios, modifications on the most relevant or critical items are
performed until a condition that determines the work items have been
sufficiently addressed. The loop will repeatedly access the most critical
item and put it back in a sorted position when it is complete. Crucially,
due to the ordering invariant we know that all work was performed when the
completed item remains the most critical. Getting this information from the
heap position avoids a (potentially more costly) check on the item state
itself.
A customized `drop` with boolean result would avoid up to two more
comparisons performed in both the last no-op refresh and Drop code but this
occurs once in each execution of the above scenario whereas refresh occurs
any number of times. Also note that the comparison overhead of Drop is only
taken if the element is mutably inspected to determine the end condition,
i.e. not when refresh itself is the break condition.
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.
Don't doc-comment BTreeMap<K, SetValZST, A>
This otherwise shows up in documentation as an empty impl block (worse, at the *top* of the docs above the public impls).
Some miscellaneous edition-related library tweaks
Some library edition tweaks that can be done separately from upgrading the whole standard library to edition 2024 (which is blocked on getting the submodules upgraded, for example)
Enable `unreachable_pub` lint in `alloc`
This PR enables the [`unreachable_pub`](https://doc.rust-lang.org/rustc/lints/listing/allowed-by-default.html#unreachable-pub) lint as warn in the `alloc` crate.
Most of changes are in the btree implementation and in tests.
*The diff was mostly generated with `./x.py fix --stage 1 library/alloc/ -- --broken-code`, as well as manual edits for code in macros and in tests.*
Continuation of #134286 and #135366
r? libs
Document collection `From` and `FromIterator` impls that drop duplicate keys.
This behavior is worth documenting because there are other plausible alternatives, such as panicking when a duplicate is encountered, and it reminds the programmer to consider whether they should, for example, coalesce duplicate keys first.
Followup to #89869.
This behavior is worth documenting because there are other plausible
alternatives, such as panicking when a duplicate is encountered, and
it reminds the programmer to consider whether they should, for example,
coalesce duplicate keys first.
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.
btree: add `{Entry,VacantEntry}::insert_entry`
This matches the recently-stabilized methods on `HashMap` entries. I've
reused tracking issue #65225 for now, but we may want to split it.
btree: don't leak value if destructor of key panics
This PR fixes a regression from https://github.com/rust-lang/rust/pull/84904.
The `BTreeMap` already attempts to handle panicking destructors of the key-value pairs by continuing to execute the remaining destructors after one destructor panicked. However, after #84904 the destructor of a value in a key-value pair gets skipped if the destructor of the key panics, only continuing with the next key-value pair. This PR reverts to the behavior before #84904 to also drop the corresponding value if the destructor of a key panics.
This avoids potential memory leaks and can fix the soundness of programs that rely on the destructors being executed (even though this should not be relied upon, because the std collections currently do not guarantee that the remaining elements are dropped after a panic in a destructor).
cc `@Amanieu` because you had opinions on panicking destructors
Add vec_deque::Iter::as_slices and friends
Add the following methods, that work similarly to VecDeque::as_slices:
- alloc::collections::vec_deque::Iter::as_slices
- alloc::collections::vec_deque::IterMut::into_slices
- alloc::collections::vec_deque::IterMut::as_slices
- alloc::collections::vec_deque::IterMut::as_mut_slices
Obtaining slices from a VecDeque iterator was not previously possible.
They are unusual methods. The docs don't really describe the cases when
they might be useful (as opposed to just `get`), and the examples don't
demonstrate the interesting cases at all.
This commit improves the docs and the examples.
The internal `btree::Recover` trait acted as a private API between
`BTreeSet` and `BTreeMap`, but we can use `pub(_)` restrictions these
days, and some of the methods don't need special handling anymore.
* `BTreeSet::get` can use `BTreeMap::get_key_value`
* `BTreeSet::take` can use `BTreeMap::remove_entry`
* `BTreeSet::replace` does need help, but this now uses a `pub(super)`
method on `BTreeMap` instead of the trait.
* `btree::Recover` is now removed.
