cacher.rs

use std::cmp::{Eq};
use std::collections::HashMap;
use std::hash::{Hash};

struct Cacher<I, O, F>
    where
    F: Fn(I) -> O,
{
    function: F,
    cache: HashMap<I, O>,
}

impl<I, O, F> Cacher<I, O, F>
    where
    I: Eq + Hash + Clone,
    O: Clone,
    F: Fn(I) -> O,
{
    fn new(fun: F) -> Cacher<I, O, F> {
        Cacher {
            function: fun,
            cache: HashMap::new(),
        }
    }

    fn call(&mut self, key: I) -> O {
        let f = &self.function;
        self.cache.entry(key.clone())
            .or_insert_with(|| (f)(key))
            .clone()
    }
}

fn some_fn(i: i32) -> i32 {
    println!("Calculating value...");
    return i * 2;
}
fn some_fn_2(_i: &str) -> i32 {
    println!("Calculating value...");
    return 2;
}

fn main() {
    let mut cacher = Cacher::new(some_fn);
    println!("{:?}", cacher.call(5));
    println!("{:?}", cacher.call(5));
    let mut cacher2 = Cacher::new(some_fn_2);
    println!("{:?}", cacher2.call("asd"));
    println!("{:?}", cacher2.call("asd"));
}