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81 lines
2.4 KiB
JavaScript
81 lines
2.4 KiB
JavaScript
var MapCache = require('../internal/MapCache');
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/** Used as the `TypeError` message for "Functions" methods. */
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var FUNC_ERROR_TEXT = 'Expected a function';
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/**
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* Creates a function that memoizes the result of `func`. If `resolver` is
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* provided it determines the cache key for storing the result based on the
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* arguments provided to the memoized function. By default, the first argument
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* provided to the memoized function is coerced to a string and used as the
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* cache key. The `func` is invoked with the `this` binding of the memoized
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* function.
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*
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* **Note:** The cache is exposed as the `cache` property on the memoized
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* function. Its creation may be customized by replacing the `_.memoize.Cache`
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* constructor with one whose instances implement the [`Map`](http://ecma-international.org/ecma-262/6.0/#sec-properties-of-the-map-prototype-object)
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* method interface of `get`, `has`, and `set`.
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*
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* @static
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* @memberOf _
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* @category Function
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* @param {Function} func The function to have its output memoized.
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* @param {Function} [resolver] The function to resolve the cache key.
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* @returns {Function} Returns the new memoizing function.
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* @example
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*
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* var upperCase = _.memoize(function(string) {
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* return string.toUpperCase();
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* });
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*
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* upperCase('fred');
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* // => 'FRED'
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*
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* // modifying the result cache
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* upperCase.cache.set('fred', 'BARNEY');
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* upperCase('fred');
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* // => 'BARNEY'
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*
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* // replacing `_.memoize.Cache`
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* var object = { 'user': 'fred' };
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* var other = { 'user': 'barney' };
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* var identity = _.memoize(_.identity);
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*
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* identity(object);
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* // => { 'user': 'fred' }
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* identity(other);
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* // => { 'user': 'fred' }
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*
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* _.memoize.Cache = WeakMap;
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* var identity = _.memoize(_.identity);
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*
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* identity(object);
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* // => { 'user': 'fred' }
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* identity(other);
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* // => { 'user': 'barney' }
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*/
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function memoize(func, resolver) {
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if (typeof func != 'function' || (resolver && typeof resolver != 'function')) {
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throw new TypeError(FUNC_ERROR_TEXT);
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}
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var memoized = function() {
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var args = arguments,
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key = resolver ? resolver.apply(this, args) : args[0],
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cache = memoized.cache;
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if (cache.has(key)) {
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return cache.get(key);
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}
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var result = func.apply(this, args);
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memoized.cache = cache.set(key, result);
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return result;
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};
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memoized.cache = new memoize.Cache;
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return memoized;
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}
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// Assign cache to `_.memoize`.
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memoize.Cache = MapCache;
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module.exports = memoize;
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