reselect/es/defaultMemoize.js

// Cache implementation based on Erik Rasmussen's `lru-memoize`:
// https://github.com/erikras/lru-memoize
var NOT_FOUND = 'NOT_FOUND';

function createSingletonCache(equals) {
  var entry;
  return {
    get: function get(key) {
      if (entry && equals(entry.key, key)) {
        return entry.value;
      }

      return NOT_FOUND;
    },
    put: function put(key, value) {
      entry = {
        key: key,
        value: value
      };
    },
    getEntries: function getEntries() {
      return entry ? [entry] : [];
    },
    clear: function clear() {
      entry = undefined;
    }
  };
}

function createLruCache(maxSize, equals) {
  var entries = [];

  function get(key) {
    var cacheIndex = entries.findIndex(function (entry) {
      return equals(key, entry.key);
    }); // We found a cached entry

    if (cacheIndex > -1) {
      var entry = entries[cacheIndex]; // Cached entry not at top of cache, move it to the top

      if (cacheIndex > 0) {
        entries.splice(cacheIndex, 1);
        entries.unshift(entry);
      }

      return entry.value;
    } // No entry found in cache, return sentinel


    return NOT_FOUND;
  }

  function put(key, value) {
    if (get(key) === NOT_FOUND) {
      // TODO Is unshift slow?
      entries.unshift({
        key: key,
        value: value
      });

      if (entries.length > maxSize) {
        entries.pop();
      }
    }
  }

  function getEntries() {
    return entries;
  }

  function clear() {
    entries = [];
  }

  return {
    get: get,
    put: put,
    getEntries: getEntries,
    clear: clear
  };
}

export var defaultEqualityCheck = function defaultEqualityCheck(a, b) {
  return a === b;
};
export function createCacheKeyComparator(equalityCheck) {
  return function areArgumentsShallowlyEqual(prev, next) {
    if (prev === null || next === null || prev.length !== next.length) {
      return false;
    } // Do this in a for loop (and not a `forEach` or an `every`) so we can determine equality as fast as possible.


    var length = prev.length;

    for (var i = 0; i < length; i++) {
      if (!equalityCheck(prev[i], next[i])) {
        return false;
      }
    }

    return true;
  };
}
// defaultMemoize now supports a configurable cache size with LRU behavior,
// and optional comparison of the result value with existing values
export function defaultMemoize(func, equalityCheckOrOptions) {
  var providedOptions = typeof equalityCheckOrOptions === 'object' ? equalityCheckOrOptions : {
    equalityCheck: equalityCheckOrOptions
  };
  var _providedOptions$equa = providedOptions.equalityCheck,
      equalityCheck = _providedOptions$equa === void 0 ? defaultEqualityCheck : _providedOptions$equa,
      _providedOptions$maxS = providedOptions.maxSize,
      maxSize = _providedOptions$maxS === void 0 ? 1 : _providedOptions$maxS,
      resultEqualityCheck = providedOptions.resultEqualityCheck;
  var comparator = createCacheKeyComparator(equalityCheck);
  var cache = maxSize === 1 ? createSingletonCache(comparator) : createLruCache(maxSize, comparator); // we reference arguments instead of spreading them for performance reasons

  function memoized() {
    var value = cache.get(arguments);

    if (value === NOT_FOUND) {
      // @ts-ignore
      value = func.apply(null, arguments);

      if (resultEqualityCheck) {
        var entries = cache.getEntries();
        var matchingEntry = entries.find(function (entry) {
          return resultEqualityCheck(entry.value, value);
        });

        if (matchingEntry) {
          value = matchingEntry.value;
        }
      }

      cache.put(arguments, value);
    }

    return value;
  }

  memoized.clearCache = function () {
    return cache.clear();
  };

  return memoized;
}