--- /dev/null
+// Copyright 2008 The Closure Library Authors. All Rights Reserved.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+// http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS-IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+/**
+ * @fileoverview Utilities for creating functions. Loosely inspired by the
+ * java classes: http://goo.gl/GM0Hmu and http://goo.gl/6k7nI8.
+ *
+ * @author nicksantos@google.com (Nick Santos)
+ */
+
+
+goog.provide('goog.functions');
+
+
+/**
+ * Creates a function that always returns the same value.
+ * @param {T} retValue The value to return.
+ * @return {function():T} The new function.
+ * @template T
+ */
+goog.functions.constant = function(retValue) {
+ return function() {
+ return retValue;
+ };
+};
+
+
+/**
+ * Always returns false.
+ * @type {function(...): boolean}
+ */
+goog.functions.FALSE = goog.functions.constant(false);
+
+
+/**
+ * Always returns true.
+ * @type {function(...): boolean}
+ */
+goog.functions.TRUE = goog.functions.constant(true);
+
+
+/**
+ * Always returns NULL.
+ * @type {function(...): null}
+ */
+goog.functions.NULL = goog.functions.constant(null);
+
+
+/**
+ * A simple function that returns the first argument of whatever is passed
+ * into it.
+ * @param {T=} opt_returnValue The single value that will be returned.
+ * @param {...*} var_args Optional trailing arguments. These are ignored.
+ * @return {T} The first argument passed in, or undefined if nothing was passed.
+ * @template T
+ */
+goog.functions.identity = function(opt_returnValue, var_args) {
+ return opt_returnValue;
+};
+
+
+/**
+ * Creates a function that always throws an error with the given message.
+ * @param {string} message The error message.
+ * @return {!Function} The error-throwing function.
+ */
+goog.functions.error = function(message) {
+ return function() {
+ throw Error(message);
+ };
+};
+
+
+/**
+ * Creates a function that throws the given object.
+ * @param {*} err An object to be thrown.
+ * @return {!Function} The error-throwing function.
+ */
+goog.functions.fail = function(err) {
+ return function() {
+ throw err;
+ }
+};
+
+
+/**
+ * Given a function, create a function that keeps opt_numArgs arguments and
+ * silently discards all additional arguments.
+ * @param {Function} f The original function.
+ * @param {number=} opt_numArgs The number of arguments to keep. Defaults to 0.
+ * @return {!Function} A version of f that only keeps the first opt_numArgs
+ * arguments.
+ */
+goog.functions.lock = function(f, opt_numArgs) {
+ opt_numArgs = opt_numArgs || 0;
+ return function() {
+ return f.apply(this, Array.prototype.slice.call(arguments, 0, opt_numArgs));
+ };
+};
+
+
+/**
+ * Creates a function that returns its nth argument.
+ * @param {number} n The position of the return argument.
+ * @return {!Function} A new function.
+ */
+goog.functions.nth = function(n) {
+ return function() {
+ return arguments[n];
+ };
+};
+
+
+/**
+ * Given a function, create a new function that swallows its return value
+ * and replaces it with a new one.
+ * @param {Function} f A function.
+ * @param {T} retValue A new return value.
+ * @return {function(...[?]):T} A new function.
+ * @template T
+ */
+goog.functions.withReturnValue = function(f, retValue) {
+ return goog.functions.sequence(f, goog.functions.constant(retValue));
+};
+
+
+/**
+ * Creates a function that returns whether its arguement equals the given value.
+ *
+ * Example:
+ * var key = goog.object.findKey(obj, goog.functions.equalTo('needle'));
+ *
+ * @param {*} value The value to compare to.
+ * @param {boolean=} opt_useLooseComparison Whether to use a loose (==)
+ * comparison rather than a strict (===) one. Defaults to false.
+ * @return {function(*):boolean} The new function.
+ */
+goog.functions.equalTo = function(value, opt_useLooseComparison) {
+ return function(other) {
+ return opt_useLooseComparison ? (value == other) : (value === other);
+ };
+};
+
+
+/**
+ * Creates the composition of the functions passed in.
+ * For example, (goog.functions.compose(f, g))(a) is equivalent to f(g(a)).
+ * @param {function(...[?]):T} fn The final function.
+ * @param {...Function} var_args A list of functions.
+ * @return {function(...[?]):T} The composition of all inputs.
+ * @template T
+ */
+goog.functions.compose = function(fn, var_args) {
+ var functions = arguments;
+ var length = functions.length;
+ return function() {
+ var result;
+ if (length) {
+ result = functions[length - 1].apply(this, arguments);
+ }
+
+ for (var i = length - 2; i >= 0; i--) {
+ result = functions[i].call(this, result);
+ }
+ return result;
+ };
+};
+
+
+/**
+ * Creates a function that calls the functions passed in in sequence, and
+ * returns the value of the last function. For example,
+ * (goog.functions.sequence(f, g))(x) is equivalent to f(x),g(x).
+ * @param {...Function} var_args A list of functions.
+ * @return {!Function} A function that calls all inputs in sequence.
+ */
+goog.functions.sequence = function(var_args) {
+ var functions = arguments;
+ var length = functions.length;
+ return function() {
+ var result;
+ for (var i = 0; i < length; i++) {
+ result = functions[i].apply(this, arguments);
+ }
+ return result;
+ };
+};
+
+
+/**
+ * Creates a function that returns true if each of its components evaluates
+ * to true. The components are evaluated in order, and the evaluation will be
+ * short-circuited as soon as a function returns false.
+ * For example, (goog.functions.and(f, g))(x) is equivalent to f(x) && g(x).
+ * @param {...Function} var_args A list of functions.
+ * @return {function(...[?]):boolean} A function that ANDs its component
+ * functions.
+ */
+goog.functions.and = function(var_args) {
+ var functions = arguments;
+ var length = functions.length;
+ return function() {
+ for (var i = 0; i < length; i++) {
+ if (!functions[i].apply(this, arguments)) {
+ return false;
+ }
+ }
+ return true;
+ };
+};
+
+
+/**
+ * Creates a function that returns true if any of its components evaluates
+ * to true. The components are evaluated in order, and the evaluation will be
+ * short-circuited as soon as a function returns true.
+ * For example, (goog.functions.or(f, g))(x) is equivalent to f(x) || g(x).
+ * @param {...Function} var_args A list of functions.
+ * @return {function(...[?]):boolean} A function that ORs its component
+ * functions.
+ */
+goog.functions.or = function(var_args) {
+ var functions = arguments;
+ var length = functions.length;
+ return function() {
+ for (var i = 0; i < length; i++) {
+ if (functions[i].apply(this, arguments)) {
+ return true;
+ }
+ }
+ return false;
+ };
+};
+
+
+/**
+ * Creates a function that returns the Boolean opposite of a provided function.
+ * For example, (goog.functions.not(f))(x) is equivalent to !f(x).
+ * @param {!Function} f The original function.
+ * @return {function(...[?]):boolean} A function that delegates to f and returns
+ * opposite.
+ */
+goog.functions.not = function(f) {
+ return function() {
+ return !f.apply(this, arguments);
+ };
+};
+
+
+/**
+ * Generic factory function to construct an object given the constructor
+ * and the arguments. Intended to be bound to create object factories.
+ *
+ * Example:
+ *
+ * var factory = goog.partial(goog.functions.create, Class);
+ *
+ * @param {function(new:T, ...)} constructor The constructor for the Object.
+ * @param {...*} var_args The arguments to be passed to the constructor.
+ * @return {!T} A new instance of the class given in {@code constructor}.
+ * @template T
+ */
+goog.functions.create = function(constructor, var_args) {
+ /**
+ * @constructor
+ * @final
+ */
+ var temp = function() {};
+ temp.prototype = constructor.prototype;
+
+ // obj will have constructor's prototype in its chain and
+ // 'obj instanceof constructor' will be true.
+ var obj = new temp();
+
+ // obj is initialized by constructor.
+ // arguments is only array-like so lacks shift(), but can be used with
+ // the Array prototype function.
+ constructor.apply(obj, Array.prototype.slice.call(arguments, 1));
+ return obj;
+};
+
+
+/**
+ * @define {boolean} Whether the return value cache should be used.
+ * This should only be used to disable caches when testing.
+ */
+goog.define('goog.functions.CACHE_RETURN_VALUE', true);
+
+
+/**
+ * Gives a wrapper function that caches the return value of a parameterless
+ * function when first called.
+ *
+ * When called for the first time, the given function is called and its
+ * return value is cached (thus this is only appropriate for idempotent
+ * functions). Subsequent calls will return the cached return value. This
+ * allows the evaluation of expensive functions to be delayed until first used.
+ *
+ * To cache the return values of functions with parameters, see goog.memoize.
+ *
+ * @param {!function():T} fn A function to lazily evaluate.
+ * @return {!function():T} A wrapped version the function.
+ * @template T
+ */
+goog.functions.cacheReturnValue = function(fn) {
+ var called = false;
+ var value;
+
+ return function() {
+ if (!goog.functions.CACHE_RETURN_VALUE) {
+ return fn();
+ }
+
+ if (!called) {
+ value = fn();
+ called = true;
+ }
+
+ return value;
+ }
+};