如何将 hashbrown 数据类型与 Rayon 并行迭代器一起使用？

Question

我有一个 hashbrown::HashSet，我正在尝试使用 Rayon 的 par_iter，但我无法找出正确的语法。

Cargo.toml

[package]
name = "basic"
version = "0.1.0"
authors = ["Me <me@example.com>"]
edition = "2018"

# See more keys and their definitions at https://doc.rust-lang.org/cargo/reference/manifest.html

[dependencies]

hashbrown = "0.9.1"
rayon = "1.5.0"

src/main.rs

use hashbrown::*;
use rayon::prelude::*;
// use hashbrown::hash_set::rayon::*;

fn main() {
    println!("Hello, world!");

    let hs = HashSet::new();
    for n in 1..100 {
        hs.insert(n);
    }

    hs.par_iter().for_each(|n| println!("n={}", n));
}

编译失败。

error[E0599]: no method named `par_iter` found for struct `hashbrown::HashSet<{integer}>` in the current scope
   --> src/main.rs:13:8
    |
13  |     hs.par_iter().for_each(|n| println!("n={}", n));
    |        ^^^^^^^^ method not found in `hashbrown::HashSet<{integer}>`
    | 
   ::: /Users/me/.cargo/registry/src/github.com-1ecc6299db9ec823/hashbrown-0.9.1/src/set.rs:114:1
    |
114 | pub struct HashSet<T, S = DefaultHashBuilder> {
    | --------------------------------------------- doesn't satisfy `_: rayon::iter::IntoParallelRefIterator`
    |
    = note: the method `par_iter` exists but the following trait bounds were not satisfied:
            `&hashbrown::HashSet<{integer}>: IntoParallelIterator`
            which is required by `hashbrown::HashSet<{integer}>: rayon::iter::IntoParallelRefIterator`

warning: unused import: `rayon::prelude`
 --> src/main.rs:2:5
  |
2 | use rayon::prelude::*;
  |     ^^^^^^^^^^^^^^
  |
  = note: `#[warn(unused_imports)]` on by default

hashset-rayon docs 表明 hashbrown::hash_set::rayon 具有与 Rayon 相关的数据类型，我知道有时我需要使用特征来提供功能。但是，如果我取消注释导入，它甚至找不到模块：

error[E0432]: unresolved import `hashbrown::hash_set::rayon`
 --> src/main.rs:3:26
  |
3 | use hashbrown::hash_set::rayon::*;
  |                          ^^^^^ could not find `rayon` in `hash_set`

我是运行 Rust 1.49.0 Mac:

$ rustup show
Default host: x86_64-apple-darwin
rustup home:  /Users/tda0106/.rustup

installed toolchains
--------------------

stable-x86_64-apple-darwin (default)
nightly-x86_64-apple-darwin

active toolchain
----------------

stable-x86_64-apple-darwin (default)
rustc 1.49.0 (e1884a8e3 2020-12-29)

有什么问题？

编辑

正如@E_net4馆长在评论中指出的那样，人造丝支持是一个特色。将依赖项更改为

[dependencies]
hashbrown = { version = "0.9.1", features = ["rayon"] }
rayon = "1.5.0"

无需额外的 use 语句即可完成这项工作。

我不清楚文档在哪里指出这一点。

Answer 1

如果您查看 hashbrown crate 的内部，您会发现 rayon 支持仅在 rayon 功能启用时才存在。您可以在 Cargo.toml:

中启用该功能

[dependencies]
hashbrown = { version = "0.9.1", features = ["rayon"] }

如何将 hashbrown 数据类型与 Rayon 并行迭代器一起使用？

How do I use hashbrown data types with Rayon parallel iterators?

rust

rayon