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use std::{hash::Hash, collections::HashMap};
pub struct Cacher<T,K,V>
where
T: Fn(K) -> V,
K: Hash + Eq,
V: Copy,
{
calculation: T,
value: HashMap<K,V>,
}
impl<T,K,V> Cacher<T,K,V>
where
T: Fn(K) -> V,
K: Hash + Eq + Copy,
V: Copy
{
pub fn new(calculation: T) -> Cacher<T,K,V> {
let value: HashMap<K,V> = HashMap::new();
Cacher {
calculation,
value,
}
}
pub fn value(&mut self, arg: K) -> V {
match self.value.get(&arg) {
Some(v) => *v,
None => {
let v = (self.calculation)(arg);
self.value.insert(arg, v);
v
},
}
}
}
#[cfg(test)]
mod tests {
use super::*;
#[test]
fn call_with_different_values() {
let mut c = Cacher::new(|a| a);
let mut c2 = Cacher::new(|a: &str| a);
let v1 = c.value(1);
let s = "hello";
let v2 = c2.value(&s[..]);
let v3 = c.value(2);
assert_eq!(v1, 1);
assert_eq!(v2, "hello");
assert_eq!(v3, 2);
}
}