1 | var MapCache = require('./_MapCache');
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2 |
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3 | /** Error message constants. */
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4 | var FUNC_ERROR_TEXT = 'Expected a function';
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5 |
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6 | /**
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7 | * Creates a function that memoizes the result of `func`. If `resolver` is
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8 | * provided, it determines the cache key for storing the result based on the
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9 | * arguments provided to the memoized function. By default, the first argument
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10 | * provided to the memoized function is used as the map cache key. The `func`
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11 | * is invoked with the `this` binding of the memoized function.
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12 | *
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13 | * **Note:** The cache is exposed as the `cache` property on the memoized
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14 | * function. Its creation may be customized by replacing the `_.memoize.Cache`
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15 | * constructor with one whose instances implement the
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16 | * [`Map`](http://ecma-international.org/ecma-262/7.0/#sec-properties-of-the-map-prototype-object)
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17 | * method interface of `clear`, `delete`, `get`, `has`, and `set`.
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18 | *
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19 | * @static
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20 | * @memberOf _
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21 | * @since 0.1.0
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22 | * @category Function
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23 | * @param {Function} func The function to have its output memoized.
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24 | * @param {Function} [resolver] The function to resolve the cache key.
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25 | * @returns {Function} Returns the new memoized function.
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26 | * @example
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27 | *
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28 | * var object = { 'a': 1, 'b': 2 };
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29 | * var other = { 'c': 3, 'd': 4 };
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30 | *
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31 | * var values = _.memoize(_.values);
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32 | * values(object);
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33 | * // => [1, 2]
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34 | *
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35 | * values(other);
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36 | * // => [3, 4]
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37 | *
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38 | * object.a = 2;
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39 | * values(object);
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40 | * // => [1, 2]
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41 | *
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42 | * // Modify the result cache.
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43 | * values.cache.set(object, ['a', 'b']);
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44 | * values(object);
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45 | * // => ['a', 'b']
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46 | *
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47 | * // Replace `_.memoize.Cache`.
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48 | * _.memoize.Cache = WeakMap;
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49 | */
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50 | function memoize(func, resolver) {
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51 | if (typeof func != 'function' || (resolver != null && typeof resolver != 'function')) {
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52 | throw new TypeError(FUNC_ERROR_TEXT);
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53 | }
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54 | var memoized = function() {
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55 | var args = arguments,
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56 | key = resolver ? resolver.apply(this, args) : args[0],
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57 | cache = memoized.cache;
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58 |
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59 | if (cache.has(key)) {
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60 | return cache.get(key);
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61 | }
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62 | var result = func.apply(this, args);
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63 | memoized.cache = cache.set(key, result) || cache;
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64 | return result;
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65 | };
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66 | memoized.cache = new (memoize.Cache || MapCache);
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67 | return memoized;
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68 | }
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69 |
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70 | // Expose `MapCache`.
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71 | memoize.Cache = MapCache;
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72 |
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73 | module.exports = memoize;
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