memoize3.js

// @flow strict

/**
 * Memoizes the provided three-argument function.
 */
export default function memoize3<
  A1: { ... } | $ReadOnlyArray<mixed>,
  A2: { ... } | $ReadOnlyArray<mixed>,
  A3: { ... } | $ReadOnlyArray<mixed>,
  R: mixed,
>(fn: (A1, A2, A3) => R): (A1, A2, A3) => R {
  let cache0;

  function memoized(a1, a2, a3) {
    if (!cache0) {
      cache0 = new WeakMap();
    }
    let cache1 = cache0.get(a1);
    let cache2;
    if (cache1) {
      cache2 = cache1.get(a2);
      if (cache2) {
        const cachedValue = cache2.get(a3);
        if (cachedValue !== undefined) {
          return cachedValue;
        }
      }
    } else {
      cache1 = new WeakMap();
      cache0.set(a1, cache1);
    }
    if (!cache2) {
      cache2 = new WeakMap();
      cache1.set(a2, cache2);
    }
    const newValue = fn(a1, a2, a3);
    cache2.set(a3, newValue);
    return newValue;
  }

  return memoized;
}