How to avoid temporary allocations when using a complex key for a HashMap?

Question

I\'m using a complex key for HashMap such that the key comprises two parts and one part is a String, and I can\'t figure out how to do lookups via

Answer 1

It sounds like you want this.

Cow will accept a &str or String.

use std::borrow::Cow;

#[derive(Debug, Eq, Hash, PartialEq)]
struct Complex<'a> {
    n: i32,
    s: Cow<'a, str>,
}

impl<'a> Complex<'a> {
    fn new>>(n: i32, s: S) -> Self {
        Complex { n: n, s: s.into() }
    }
}

fn main() {
    let mut m = std::collections::HashMap::, i32>::new();
    m.insert(Complex::new(42, "foo"), 123);

    assert_eq!(123, *m.get(&Complex::new(42, "foo")).unwrap());
}

A comment about lifetime parameters:

If you don't like the lifetime parameter and you only need to work with &'static str or String then you can use Cow<'static, str> and remove the other lifetime parameters from the impl block and struct definition.