Code shared from the Rust Playground

playground.rs

use std::collections::HashMap;

struct Foo {
    d: HashMap<String, f32>
}

impl Foo {
    fn get(&mut self, s: &str) -> Option<&f32> {
        if !self.d.contains_key(s) {
            self.d.insert(s.to_string(), 0.0);
        }
        self.d.get(s)
    }
}

fn main() {
    let mut foo = Foo {
        d: HashMap::new() 
    };
    
    let mut saved = Vec::new();
    
    for _i in 1..3 {
        let l = foo.get("a");
        saved.push(l);
    }
}