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