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101 строка
2.6 KiB
Markdown
101 строка
2.6 KiB
Markdown
# `id-arena`
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[![](https://img.shields.io/crates/v/id-arena.svg)](https://crates.io/crates/id-arena)
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[![](https://img.shields.io/crates/d/id-arena.svg)](https://crates.io/crates/id-arena)
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[![Travis CI Build Status](https://travis-ci.org/fitzgen/id-arena.svg?branch=master)](https://travis-ci.org/fitzgen/id-arena)
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A simple, id-based arena.
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### Id-based
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Allocate objects and get an identifier for that object back, *not* a
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reference to the allocated object. Given an id, you can get a shared or
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exclusive reference to the allocated object from the arena. This id-based
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approach is useful for constructing mutable graph data structures.
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If you want allocation to return a reference, consider [the `typed-arena`
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crate](https://github.com/SimonSapin/rust-typed-arena/) instead.
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### No Deletion
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This arena does not support deletion, which makes its implementation simple
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and allocation fast. If you want deletion, you need a way to solve the ABA
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problem. Consider using [the `generational-arena`
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crate](https://github.com/fitzgen/generational-arena) instead.
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### Homogeneous
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This crate's arenas can only contain objects of a single type `T`. If you
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need an arena of objects with heterogeneous types, consider another crate.
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### `#![no_std]` Support
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Requires the `alloc` nightly feature. Disable the on-by-default `"std"` feature:
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```toml
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[dependencies.id-arena]
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version = "2"
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default-features = false
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```
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### `rayon` Support
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If the `rayon` feature of this crate is activated:
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```toml
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[dependencies]
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id-arena = { version = "2", features = ["rayon"] }
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```
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then you can use [`rayon`](https://crates.io/crates/rayon)'s support for
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parallel iteration. The `Arena` type will have a `par_iter` family of
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methods where appropriate.
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### Example
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```rust
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use id_arena::{Arena, Id};
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type AstNodeId = Id<AstNode>;
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#[derive(Debug, Eq, PartialEq)]
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pub enum AstNode {
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Const(i64),
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Var(String),
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Add {
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lhs: AstNodeId,
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rhs: AstNodeId,
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},
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Sub {
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lhs: AstNodeId,
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rhs: AstNodeId,
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},
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Mul {
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lhs: AstNodeId,
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rhs: AstNodeId,
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},
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Div {
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lhs: AstNodeId,
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rhs: AstNodeId,
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},
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}
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let mut ast_nodes = Arena::<AstNode>::new();
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// Create the AST for `a * (b + 3)`.
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let three = ast_nodes.alloc(AstNode::Const(3));
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let b = ast_nodes.alloc(AstNode::Var("b".into()));
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let b_plus_three = ast_nodes.alloc(AstNode::Add {
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lhs: b,
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rhs: three,
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});
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let a = ast_nodes.alloc(AstNode::Var("a".into()));
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let a_times_b_plus_three = ast_nodes.alloc(AstNode::Mul {
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lhs: a,
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rhs: b_plus_three,
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});
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// Can use indexing to access allocated nodes.
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assert_eq!(ast_nodes[three], AstNode::Const(3));
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```
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