如何在人造丝并行迭代器中使用哈希布朗数据类型？

Question

我有一个hashbrown::HashSet，我试着用它来使用人造丝的par_iter，但是我找不出正确的语法。

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));
}

这无法编译。

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

哈希集-人造丝文档建议hashbrown::hash_set::rayon有一个与人造丝相关的数据类型，而且我知道有时我需要使用特性来使功能可用。但是，如果取消对导入的注释，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`

我在Mac上运行Rust 1.49.0：

$ 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)

有什么问题吗？

编辑

正如策展人@E_net4在评论中指出的那样，人造丝支持是在一个特性中。将依赖项更改为

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

使此工作，而不需要额外的使用语句。

我不清楚文档在哪里表明了这一点。

Answer 1

如果您查看板条箱内部，您将看到只有当启用了rayon特性时，才会出现rayon支持。您可以在Cargo.toml中启用该功能。

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