Blog Post: Memory Management in Rust and Swift

[leonardo]

This is an example code from one answer by matklad:

Rustify combinators application to create Map from String

If you don't mind some unwrap() this is a possible solution: fn main() { use std::collections::HashMap; let tags_string = "KEY1=VAL1,KEY2=VAL2"; let tags = tags_string .split(',') .map(|kv| kv.split('=')) .map(|mut kv| (kv.next().unwrap().into(), kv.next().unwrap().into())) .collect::<HashMap<String, String>>(); println!("{:?}", tags); } But we can do a bit better with: You can write …

use std::collections::HashMap;

fn main() {
    let tags_string = "KEY1=VAL1,KEY2=VAL2";
    let tags: HashMap<String, String> = tags_string.split(',')
        .map(|kv| kv.split('=').collect::<Vec<&str>>())
        .map(|vec| {
            assert_eq!(vec.len(), 2);
            (vec[0].to_string(), vec[1].to_string())
        })
        .collect();
}

It contains a .collect::<Vec<_>>(), that's a heap allocation of a 2-items long vector for each input row. I'd like a future Rust compiler to perform Escape Analysis on such code and remove all those heap allocations.