memoized.rs

use std::collections::HashMap;
use std::hash::Hash;

struct Memoize<F, T1, T2> where F: Fn(&T1) -> T2 {
    cache: HashMap<T1, T2>,
    func: F,
}

impl<F, T1, T2> Memoize<F, T1, T2> where F: Fn(&T1) -> T2, T1: Eq + Hash, T2: Clone {
    fn new(func: F) -> Memoize<F, T1, T2> {
        Memoize {cache: HashMap::new(), func}
    }
    
    fn get(&mut self, k : T1) -> T2 {
        match self.cache.get(&k) {
            Some(v) => v.clone(),
            None => {
                let v = (self.func)(&k);
                self.cache.insert(k, v.clone());
                v
            }
        }
        
    }
}

fn main() {
    let mut f = Memoize::new(|x| x + 2);
    println!("Hello, world! {} {}", f.get(2), f.get(5));
}

Memoization example in Rust