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* @license Apache-2.0
*
* Copyright (c) 2018 The Stdlib Authors.
*
* 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.
*/
'use strict';
// MODULES //
var isFunction = require( '@stdlib/assert/is-function' );
var setReadOnly = require( '@stdlib/utils/define-nonenumerable-read-only-property' );
var identity = require( '@stdlib/utils/identity-function' );
var hasOwnProp = require( '@stdlib/assert/has-own-property' );
var format = require( '@stdlib/string/format' );
// MAIN //
/**
* Returns a memoized function.
*
* @param {Function} fcn - function to memoize
* @param {Function} [hashFunction] - function to map a set of arguments to a single value identifying that set
* @throws {TypeError} first argument must be a function
* @throws {TypeError} second argument must be a function
* @returns {Function} memoized function
*
* @example
* function factorial( n ) {
* var prod;
* var i;
* prod = 1;
* for ( i = n; i > 1; i-- ) {
* prod *= i;
* }
* return prod;
* }
*
* var memoized = memoize( factorial );
*
* var v = memoized( 5 );
* // returns 120
*
* v = memoized( 5 );
* // returns 120
*/
function memoize( fcn, hashFunction ) {
var toKey;
var cache;
if ( !isFunction( fcn ) ) {
throw new TypeError( format( 'invalid argument. First argument must be a function. Value: `%s`.', fcn ) );
}
if ( arguments.length < 2 ) {
toKey = identity;
} else {
toKey = hashFunction;
if ( !isFunction( toKey ) ) {
throw new TypeError( format( 'invalid argument. Hash function argument must be a function. Value: `%s`.', toKey ) );
}
}
cache = {};
setReadOnly( memoized, 'cache', cache );
return memoized;
/**
* Memoized function.
*
* @private
* @param {...*} args - function arguments
* @returns {*} memoized function result
*/
function memoized() {
var args;
var out;
var key;
var i;
args = new Array( arguments.length );
for ( i = 0; i < arguments.length; i++ ) {
args[ i ] = arguments[ i ];
}
key = toKey( args ).toString();
if ( hasOwnProp( cache, key ) ) {
return cache[ key ];
}
out = fcn.apply( null, args );
cache[ key ] = out;
return out;
}
}
// EXPORTS //
module.exports = memoize;
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