rust_memoization_example.rs

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

struct Cacher<T, U, V>
where
    T: Fn(U) -> V,
    U: Hash + Eq + Clone,
    V: Copy,
{
    calculation: T,
    values: HashMap<U, V>,
}

impl<T, U, V> Cacher<T, U, V>
where
    T: Fn(U) -> V,
    U: Hash + Eq + Clone,
    V: Copy,
{
    fn new(calculation: T) -> Cacher<T, U, V> {
        Cacher {
            calculation,
            values: HashMap::new(),
        }
    }

    fn value(&mut self, arg: U) -> V {
        match self.values.get(&arg).map(|v| v.clone()) {
            Some(v) => v,
            None => {
                let v: V = (self.calculation)(arg.clone());

                self.values.insert(arg, v.clone());

                v
            }
        }
    }
}

fn main() {
    let mut cacher = Cacher::new(|i: i32| i + 10);

    println!("{}", cacher.value(10));
}