// 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 [email protected] (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;
}
};
/**
* Wraps a function to allow it to be called, at most, once. All
* additional calls are no-ops.
*
* This is particularly useful for initialization functions
* that should be called, at most, once.
*
* @param {function():*} f Function to call.
* @return {function():undefined} Wrapped function.
*/
goog.functions.once = function(f) {
// Keep a reference to the function that we null out when we're done with
// it -- that way, the function can be GC'd when we're done with it.
var inner = f;
return function() {
if (inner) {
var tmp = inner;
inner = null;
tmp();
}
};
};
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