Crate fn_memo

A library for creating the memoization of a function that uses cache to improve the performance.

You can create the memoization with unsync::memoize function. It uses a HashMap for caching.

use fn_memo::{FnMemo, unsync};

let mul_2 = unsync::memoize(|n| {
    println!("Evaluating {}", n);
    n * 2
});

assert_eq!(0, mul_2.call(0)); // Output "Evaluating 0."
assert_eq!(4, mul_2.call(2)); // Output "Evaluating 2."
assert_eq!(10, mul_2.call(5)); // Output "Evaluating 5."
assert_eq!(4, mul_2.call(2)); // No output. The result is cached.
mul_2.clear_cache();
assert_eq!(4, mul_2.call(2)); // Output "Evaluating 2."

The memoize function takes a RecurFn argument, which allows you to memoize a recursive function and each recursion result will be cached. See the documentation of recur-fn crate for details.

For the sequence (i.e. the function that takes an usize as argument), you can also use unsync::memoize_seq. It uses a Vec as a bucket to cache, so it has a better performance but takes the memory proportional to the largest argument of the cache.

You can costumize the data structure of the cache by implementing unsync::Cache trait and create memoization with unsync::Memo::new method. For more details, see the documentation.

The APIs under unsync namespace are for single-thread memoization. The result of unsync::memoize does not Send even the cached function does.

use std::{sync::Arc, thread};
use fn_memo::{FnMemo, unsync};

let f = Arc::new(unsync::memoize(|n: i32| n));
thread::spawn(move || { f }); // Compile Error

The synchronize version APIs are under sync namespace.

use fn_memo::{FnMemo, sync};
use std::thread;
use std::sync::Arc;

let mul_2 = Arc::new(sync::memoize(|n| {
    println!("Evaluating {}", n);
    n * 2
}));

let mut threads = Vec::new();
for _ in 0..4 {
    threads.push(thread::spawn({
        let mul_2 = Arc::clone(&mul_2);
        move || {
            for n in 0..10 {
                assert_eq!(n*2, mul_2.call(n));
            }
        }
    }));
}
for thread in threads {
    thread.join().unwrap();
}

The code above will output the evaluation from 0 to 9. Each of them is outputed only once.

Modules

sync
unsync

Traits

FnMemo

The memoized function.