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// 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 Tool for caching the result of expensive deterministic
* functions.
*
* @see http://en.wikipedia.org/wiki/Memoization
*
*/
goog.provide('goog.memoize');
/**
* Decorator around functions that caches the inner function's return values.
* @param {Function} f The function to wrap. Its return value may only depend
* on its arguments and 'this' context. There may be further restrictions
* on the arguments depending on the capabilities of the serializer used.
* @param {function(number, Object): string=} opt_serializer A function to
* serialize f's arguments. It must have the same signature as
* goog.memoize.simpleSerializer. It defaults to that function.
* @this {Object} The object whose function is being wrapped.
* @return {!Function} The wrapped function.
*/
goog.memoize = function(f, opt_serializer) {
var functionUid = goog.getUid(f);
var serializer = opt_serializer || goog.memoize.simpleSerializer;
return function() {
if (goog.memoize.ENABLE_MEMOIZE) {
// In the strict mode, when this function is called as a global function,
// the value of 'this' is undefined instead of a global object. See:
// https://developer.mozilla.org/en/JavaScript/Strict_mode
var thisOrGlobal = this || goog.global;
// Maps the serialized list of args to the corresponding return value.
var cache = thisOrGlobal[goog.memoize.CACHE_PROPERTY_] ||
(thisOrGlobal[goog.memoize.CACHE_PROPERTY_] = {});
var key = serializer(functionUid, arguments);
return cache.hasOwnProperty(key) ? cache[key] :
(cache[key] = f.apply(this, arguments));
} else {
return f.apply(this, arguments);
}
};
};
/**
* @define {boolean} Flag to disable memoization in unit tests.
*/
goog.memoize.ENABLE_MEMOIZE = true;
/**
* Clears the memoization cache on the given object.
* @param {Object} cacheOwner The owner of the cache. This is the {@code this}
* context of the memoized function.
*/
goog.memoize.clearCache = function(cacheOwner) {
cacheOwner[goog.memoize.CACHE_PROPERTY_] = {};
};
/**
* Name of the property used by goog.memoize as cache.
* @type {string}
* @private
*/
goog.memoize.CACHE_PROPERTY_ = 'closure_memoize_cache_';
/**
* Simple and fast argument serializer function for goog.memoize.
* Supports string, number, boolean, null and undefined arguments. Doesn't
* support \x0B characters in the strings.
* @param {number} functionUid Unique identifier of the function whose result
* is cached.
* @param {Object} args The arguments that the function to memoize is called
* with. Note: it is an array-like object, because supports indexing and
* has the length property.
* @return {string} The list of arguments with type information concatenated
* with the functionUid argument, serialized as \x0B-separated string.
*/
goog.memoize.simpleSerializer = function(functionUid, args) {
var context = [functionUid];
for (var i = args.length - 1; i >= 0; --i) {
context.push(typeof args[i], args[i]);
}
return context.join('\x0B');
};
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