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Add more links between hash and btree collections
- Link from `core::hash` to `HashMap` and `HashSet`
- Link from HashMap and HashSet to the module-level documentation on
when to use the collection
- Link from several collections to Wikipedia articles on the general
concept
See also https://github.com/rust-lang/rust/pull/81989#issuecomment-783920840.
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Fixes #82080
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Add {BTreeMap,HashMap}::try_insert
`{BTreeMap,HashMap}::insert(key, new_val)` returns `Some(old_val)` if the key was already in the map. It's often useful to assert no duplicate values are inserted.
We experimented with `map.insert(key, val).unwrap_none()` (https://github.com/rust-lang/rust/issues/62633), but decided that that's not the kind of method we'd like to have on `Option`s.
`insert` always succeeds because it replaces the old value if it exists. One could argue that `insert()` is never the right method for panicking on duplicates, since already handles that case by replacing the value, only allowing you to panic after that already happened.
This PR adds a `try_insert` method that instead returns a `Result::Err` when the key already exists. This error contains both the `OccupiedEntry` and the value that was supposed to be inserted. This means that unwrapping that result gives more context:
```rust
map.insert(10, "world").unwrap_none();
// thread 'main' panicked at 'called `Option::unwrap_none()` on a `Some` value: "hello"', src/main.rs:8:29
```
```rust
map.try_insert(10, "world").unwrap();
// thread 'main' panicked at 'called `Result::unwrap()` on an `Err` value:
// OccupiedError { key: 10, old_value: "hello", new_value: "world" }', src/main.rs:6:33
```
It also allows handling the failure in any other way, as you have full access to the `OccupiedEntry` and the value.
`try_insert` returns a reference to the value in case of success, making it an alternative to `.entry(key).or_insert(value)`.
r? ```@Amanieu```
Fixes https://github.com/rust-lang/rfcs/issues/3092
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- Link from `core::hash` to `HashMap` and `HashSet`
- Link from HashMap and HashSet to the module-level documentation on
when to use the collection
- Link from several collections to Wikipedia articles on the general
concept
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Add doc aliases for "delete"
This patch adds doc aliases for "delete". The added aliases are supposed to reference usages `delete` in other programming languages.
- `HashMap::remove`, `BTreeMap::remove` -> `Map#delete` and `delete` keyword in JavaScript.
- `HashSet::remove`, `BTreeSet::remove` -> `Set#delete` in JavaScript.
- `mem::drop` -> `delete` keyword in C++.
- `fs::remove_file`, `fs::remove_dir`, `fs::remove_dir_all`-> `File#delete` in Java, `File#delete` and `Dir#delete` in Ruby.
Before this change, searching for "delete" in documentation returned no results.
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This patch adds doc aliases for "delete". The added aliases are
supposed to reference usages `delete` in other programming
languages.
- `HashMap::remove`, `BTreeMap::remove` -> `Map#delete` and `delete`
keyword in JavaScript.
- `HashSet::remove`, `BTreeSet::remove` -> `Set#delete` in JavaScript.
- `mem::drop` -> `delete` keyword in C++.
- `fs::remove_file`, `fs::remove_dir`, `fs::remove_dir_all`
-> `File#delete` in Java, `File#delete` and `Dir#delete` in Ruby.
Before this change, searching for "delete" in documentation
returned no results.
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Fixes #81548.
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Stabilize or_insert_with_key
Stabilizes the `or_insert_with_key` feature from https://github.com/rust-lang/rust/issues/71024. This allows inserting key-derived values when a `HashMap`/`BTreeMap` entry is vacant.
The difference between this and `.or_insert_with(|| ... )` is that this provides a reference to the key to the closure after it is moved with `.entry(key_being_moved)`, avoiding the need to copy or clone the key.
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Doc change: Remove mention of `fnv` in HashMap
Disclaimer: I am the author of [aHash](https://github.com/tkaitchuck/aHash).
This changes the Rustdoc in `HashMap` from mentioning the `fnv` crate to mentioning the `aHash` crate, as an alternative `Hasher` implementation.
### Why
Fnv [has poor hash quality](https://github.com/rurban/smhasher), is [slow for larger keys](https://github.com/tkaitchuck/aHash/blob/master/compare/readme.md#speed), and does not provide dos resistance, because it is unkeyed (this can also cause [other problems](https://accidentallyquadratic.tumblr.com/post/153545455987/rust-hash-iteration-reinsertion)).
Fnv has acceptable performance for integers and has very poor performance with keys >32 bytes. This is the reason it was removed from the standard library in https://github.com/rust-lang/rust/pull/37229 .
Because regardless of which dimension you value, there are better alternatives, it does not make sense for anyone to consider using `fnv`.
The text mentioning `fnv` in the standard library continues to create confusion: https://github.com/rust-lang/hashbrown/issues/153 https://github.com/rust-lang/hashbrown/issues/9 . There are also a number of [crates using it](https://crates.io/crates/fnv/reverse_dependencies) a great many of which are hashing strings (Which is when Fnv is the [worst](https://github.com/cbreeden/fxhash#benchmarks), [possible](https://github.com/tkaitchuck/aHash#speed), [choice](http://cglab.ca/~abeinges/blah/hash-rs/).)
I think aHash makes the most sense to mention as an alternative because it is the most credible option (in my obviously biased opinion). It offers [good performance on numbers and strings](https://github.com/tkaitchuck/aHash/blob/master/compare/readme.md#speed), is [of high quality](https://github.com/tkaitchuck/aHash#hash-quality), and [provides dos resistance](https://github.com/tkaitchuck/aHash/wiki/How-aHash-is-resists-DOS-attacks). It is popular (see [stats](https://crates.io/crates/ahash)) and is the default hasher for [hashbrown](https://crates.io/crates/hashbrown) and [dashmap](https://crates.io/crates/dashmap) which are the most popular alternative hashmaps. Finally it does not have any of the [`gotcha` cases](https://github.com/tkaitchuck/aHash#fxhash) that `FxHash` suffers from. (Which is the other popular hashing option when DOS attacks are not a concern)
Signed-off-by: Tom Kaitchuck <tom.kaitchuck@emc.com>
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Co-authored-by: Mara Bos <m-ou.se@m-ou.se>
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Signed-off-by: Tom Kaitchuck <Tom.Kaitchuck@gmail.com>
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Signed-off-by: Tom Kaitchuck <tom.kaitchuck@emc.com>
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Minor `hash_map` doc adjustments + item attribute orderings
This PR is really a couple visual changes glued together:
1. Some of the doc comments for items in `std::collections::hash_map` referenced the names of types without escaping their formatting (e.g. using "VacantEntry" instead of "`VacantEntry`") - the ones I could find were changed to the latter
2. The vast majority of pre-item attributes seem to place doc comments as the first attribute (instead of things like `#[feature(...)]`), so the few that had the other order were changed.
3. Also ordering related: the general trend seems to be that `#[feature]` attributes follow `#[inline]`, so I swapped the two lines in places where that ordering was reversed. This is primarily a change based on stylistic continuity and aesthetics - I'm not sure how important that actually is / should be.
I figured this would be pretty uncontroversial, but some of these might have been intentional for reasons I don't know about - if so, I'd be happy to remove the relevant changes. Of these, the final set of changes is probably the most unnecessary, so it also might be better to leave those out (in favor of reducing code churn).
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Fix Debug implementations of some of the HashMap and BTreeMap iterator types
HashMap's `ValuesMut`, BTreeMaps `ValuesMut`, IntoValues and `IntoKeys` structs were printing both keys and values on their Debug implementations. But they are iterators over either keys or values. Irrelevant values should not be visible. With this PR, they only show relevant fields.
This fixes #75297.
[Here's an example code.](https://play.rust-lang.org/?version=nightly&mode=debug&edition=2018&gist=0c79356ed860e347a0c1a205616f93b7) This prints this on nightly:
```
ValuesMut { inner: IterMut { range: [(1, "hello"), (2, "goodbye")], length: 2 } }
IntoKeys { inner: [(1, "hello"), (2, "goodbye")] }
IntoValues { inner: [(1, "hello"), (2, "goodbye")] }
[(2, "goodbye"), (1, "hello")]
```
After the patch this example prints these instead:
```
["hello", "goodbye"]
["hello", "goodbye"]
[1, 2]
["hello", "goodbye"]
```
I didn't add test cases for them, since I couldn't see any tests for Debug implementations anywhere. But please let me know if I should add it to a specific place.
r? @dtolnay
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Add missing code examples on HashMap types
r? @Dylan-DPC
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Add missing examples on HashSet iter types
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Implements #59618.
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Use Arc::clone and Rc::clone in documentation
This PR replaces uses of `x.clone()` by `Rc::clone(&x)` (or `Arc::clone(&x)`) to better match the documentation for those types.
@rustbot modify labels: T-doc
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Also doing fmt inplace as requested.
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