headroom/frontend/node_modules/memoize-weak/lib/memoize.js

function isPrimitive(value) {
  return ((typeof value !== 'object') && (typeof value !== 'function')) || (value === null);
}

function MapTree() {
  this.childBranches = new WeakMap();
  this.primitiveKeys = new Map();
  this.hasValue = false;
  this.value = undefined;
}

MapTree.prototype.has = function has(key) {
  var keyObject = (isPrimitive(key) ? this.primitiveKeys.get(key) : key);
  return (keyObject ? this.childBranches.has(keyObject) : false);
};

MapTree.prototype.get = function get(key) {
  var keyObject = (isPrimitive(key) ? this.primitiveKeys.get(key) : key);
  return (keyObject ? this.childBranches.get(keyObject) : undefined);
};

MapTree.prototype.resolveBranch = function resolveBranch(key) {
  if (this.has(key)) { return this.get(key); }
  var newBranch = new MapTree();
  var keyObject = this.createKey(key);
  this.childBranches.set(keyObject, newBranch);
  return newBranch;
};

MapTree.prototype.setValue = function setValue(value) {
  this.hasValue = true;
  return (this.value = value);
};

MapTree.prototype.createKey = function createKey(key) {
  if (isPrimitive(key)) {
    var keyObject = {};
    this.primitiveKeys.set(key, keyObject);
    return keyObject;
  }
  return key;
};

MapTree.prototype.clear = function clear() {
  if (arguments.length === 0) {
    this.childBranches = new WeakMap();
    this.primitiveKeys.clear();
    this.hasValue = false;
    this.value = undefined;
  } else if (arguments.length === 1) {
    var key = arguments[0];
    if (isPrimitive(key)) {
      var keyObject = this.primitiveKeys.get(key);
      if (keyObject) {
        this.childBranches.delete(keyObject);
        this.primitiveKeys.delete(key);
      }
    } else {
      this.childBranches.delete(key);
    }
  } else {
    var childKey = arguments[0];
    if (this.has(childKey)) {
      var childBranch = this.get(childKey);
      childBranch.clear.apply(childBranch, Array.prototype.slice.call(arguments, 1));
    }
  }
};

module.exports = function memoize(fn) {
  var argsTree = new MapTree();

  function memoized() {
    var args = Array.prototype.slice.call(arguments);
    var argNode = args.reduce(function getBranch(parentBranch, arg) {
      return parentBranch.resolveBranch(arg);
    }, argsTree);
    if (argNode.hasValue) { return argNode.value; }
    var value = fn.apply(null, args);
    return argNode.setValue(value);
  }

  memoized.clear = argsTree.clear.bind(argsTree);

  return memoized;
};