How do I create a HashMap literal?

Question

How I can create a HashMap literal in Rust? In Python I can do it so:

hashmap = {
   \'element0\': {
       \'name\': \'My New Element\',
       \'childs\':          


        

Answer 1

For one element

If you wish to initialize the map with only one element in one line (and without visible mutation in your code), you could do:

let map: HashMap<&'static str, u32> = Some(("answer", 42)).into_iter().collect();

This is thanks to the usefulness of Option being able to become an Iterator using into_iter().

In real code, you probably don't need to help the compiler with the type:

use std::collections::HashMap;

fn john_wick() -> HashMap<&'static str, u32> {
    Some(("answer", 42)).into_iter().collect()
}

fn main() {
    let result = john_wick();

    let mut expected = HashMap::new();
    expected.insert("answer", 42);

    assert_eq!(result, expected);
}

There is also a way to chain this to have more than one element doing something like Some(a).into_iter().chain(Some(b).into_iter()).collect(), but this is longer, less readable and probably has some optimization issues, so I advise against it.