catcher.rs

struct Catcher<K, V, T>
where
    K: Eq + Hash + Copy,
    V: Copy,
    T: Fn(K) -> V
{
    calculation: T,
    cache: HashMap<K, V>,
}

impl<K, V, T> Catcher<K, V, T>
where
    K: Eq + Hash + Copy,
    V: Copy,
    T: Fn(K) -> V
{
    fn new(calculation: T) -> Catcher<K, V, T> {
        Catcher {
            calculation,
            cache: HashMap::new(),
        }
    }

    fn value(&mut self, arg: K) -> V {
        if let Some(v) = self.cache.get(&arg) {
            return *v
        }
        let v = (self.calculation)(arg);
        self.cache.insert(arg, v);
        v
    }
}