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Empowering everyone to build reliable and efficient software.
37f02320bc
Rewrite the BTreeMap cursor API using gaps Tracking issue: #107540 Currently, a `Cursor` points to a single element in the tree, and allows moving to the next or previous element while mutating the tree. However this was found to be confusing and hard to use. This PR completely refactors cursors to instead point to a gap between two elements in the tree. This eliminates the need for a "ghost" element that exists after the last element and before the first one. Additionally, `upper_bound` and `lower_bound` now have a much clearer meaning. The ability to mutate keys is also factored out into a separate `CursorMutKey` type which is unsafe to create. This makes the API easier to use since it avoids duplicated versions of each method with and without key mutation. API summary: ```rust impl<K, V> BTreeMap<K, V> { fn lower_bound<Q>(&self, bound: Bound<&Q>) -> Cursor<'_, K, V> where K: Borrow<Q> + Ord, Q: Ord; fn lower_bound_mut<Q>(&mut self, bound: Bound<&Q>) -> CursorMut<'_, K, V> where K: Borrow<Q> + Ord, Q: Ord; fn upper_bound<Q>(&self, bound: Bound<&Q>) -> Cursor<'_, K, V> where K: Borrow<Q> + Ord, Q: Ord; fn upper_bound_mut<Q>(&mut self, bound: Bound<&Q>) -> CursorMut<'_, K, V> where K: Borrow<Q> + Ord, Q: Ord; } struct Cursor<'a, K: 'a, V: 'a>; impl<'a, K, V> Cursor<'a, K, V> { fn next(&mut self) -> Option<(&'a K, &'a V)>; fn prev(&mut self) -> Option<(&'a K, &'a V)>; fn peek_next(&self) -> Option<(&'a K, &'a V)>; fn peek_prev(&self) -> Option<(&'a K, &'a V)>; } struct CursorMut<'a, K: 'a, V: 'a>; impl<'a, K, V> CursorMut<'a, K, V> { fn next(&mut self) -> Option<(&K, &mut V)>; fn prev(&mut self) -> Option<(&K, &mut V)>; fn peek_next(&mut self) -> Option<(&K, &mut V)>; fn peek_prev(&mut self) -> Option<(&K, &mut V)>; unsafe fn insert_after_unchecked(&mut self, key: K, value: V); unsafe fn insert_before_unchecked(&mut self, key: K, value: V); fn insert_after(&mut self, key: K, value: V) -> Result<(), UnorderedKeyError>; fn insert_before(&mut self, key: K, value: V) -> Result<(), UnorderedKeyError>; fn remove_next(&mut self) -> Option<(K, V)>; fn remove_prev(&mut self) -> Option<(K, V)>; fn as_cursor(&self) -> Cursor<'_, K, V>; unsafe fn with_mutable_key(self) -> CursorMutKey<'a, K, V, A>; } struct CursorMutKey<'a, K: 'a, V: 'a>; impl<'a, K, V> CursorMut<'a, K, V> { fn next(&mut self) -> Option<(&mut K, &mut V)>; fn prev(&mut self) -> Option<(&mut K, &mut V)>; fn peek_next(&mut self) -> Option<(&mut K, &mut V)>; fn peek_prev(&mut self) -> Option<(&mut K, &mut V)>; unsafe fn insert_after_unchecked(&mut self, key: K, value: V); unsafe fn insert_before_unchecked(&mut self, key: K, value: V); fn insert_after(&mut self, key: K, value: V) -> Result<(), UnorderedKeyError>; fn insert_before(&mut self, key: K, value: V) -> Result<(), UnorderedKeyError>; fn remove_next(&mut self) -> Option<(K, V)>; fn remove_prev(&mut self) -> Option<(K, V)>; fn as_cursor(&self) -> Cursor<'_, K, V>; unsafe fn with_mutable_key(self) -> CursorMutKey<'a, K, V, A>; } struct UnorderedKeyError; ``` |
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The Rust Programming Language
This is the main source code repository for Rust. It contains the compiler, standard library, and documentation.
Note: this README is for users rather than contributors. If you wish to contribute to the compiler, you should read CONTRIBUTING.md instead.
Table of Contents
Quick Start
Read "Installation" from The Book.
Installing from Source
If you really want to install from source (though this is not recommended), see INSTALL.md.
Getting Help
See https://www.rust-lang.org/community for a list of chat platforms and forums.
Contributing
See CONTRIBUTING.md.
License
Rust is primarily distributed under the terms of both the MIT license and the Apache License (Version 2.0), with portions covered by various BSD-like licenses.
See LICENSE-APACHE, LICENSE-MIT, and COPYRIGHT for details.
Trademark
The Rust Foundation owns and protects the Rust and Cargo trademarks and logos (the "Rust Trademarks").
If you want to use these names or brands, please read the media guide.
Third-party logos may be subject to third-party copyrights and trademarks. See Licenses for details.