加入& str的迭代器 [英] Join iterator of &str

问题描述

将 Iterator<& str> 转换为 String 并穿插一些常量字符串(例如"\ n" )?

What is the canonical method to convert an Iterator<&str> to a String, interspersed with some constant string (e.g. "\n")?

例如，给定:

let xs = vec!["first", "second", "third"];
let it = xs.iter();

有一种方法可以通过收集一些 Iterable 和 join 生成结果来生成字符串 s :

There is a way to produce a string s by collecting into some Iterable and joining the result:

let s = it
    .map(|&x| x)
    .collect::<Vec<&str>>()
    .join("\n");

但是，这不必要地为 Vec& str> 分配了内存.有更直接的方法吗?

However, this unnecessarily allocates memory for a Vec<&str>. Is there a more direct method?

推荐答案

您可以使用 itertools 板条箱.我使用 intersperse 助手，它几乎等同于迭代器的 join .

You could use the itertools crate for that. I use the intersperse helper in the example, it is pretty much the join equivalent for iterators.

cloned()来将&& str 项转换为& str 项，它没有进行任何分配.当 rust@1.36 稳定发行时，最终可以将其替换为 copied().

cloned() is needed to convert &&str items to &str items, it is not doing any allocations. It can be eventually replaced by copied() when rust@1.36 gets a stable release.

use itertools::Itertools; // 0.8.0

fn main() {
    let words = ["alpha", "beta", "gamma"];
    let merged: String = words.iter().cloned().intersperse(", ").collect();
    assert_eq!(merged, "alpha, beta, gamma");
}

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