Join iterator of &str [duplicate]

Question

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

For instance, given:

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

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");

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

Answer 1

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() is needed to convert &&str items to &str items, it is not doing any allocations. It can be eventually replaced by copied() when [email protected] 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");
}

Playground