205 lines
4.0 KiB
Markdown
205 lines
4.0 KiB
Markdown
<!--
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@license Apache-2.0
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Copyright (c) 2018 The Stdlib Authors.
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Licensed under the Apache License, Version 2.0 (the "License");
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you may not use this file except in compliance with the License.
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You may obtain a copy of the License at
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http://www.apache.org/licenses/LICENSE-2.0
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Unless required by applicable law or agreed to in writing, software
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distributed under the License is distributed on an "AS IS" BASIS,
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WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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See the License for the specific language governing permissions and
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limitations under the License.
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-->
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# memoize
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> Memoize a function.
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<!-- Section to include introductory text. Make sure to keep an empty line after the intro `section` element and another before the `/section` close. -->
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<section class="intro">
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</section>
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<!-- /.intro -->
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<!-- Package usage documentation. -->
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<section class="usage">
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## Usage
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```javascript
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var memoize = require( '@stdlib/utils/memoize' );
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```
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#### memoize( fcn\[, hashFunction] )
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Memoizes a function.
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```javascript
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var randu = require( '@stdlib/random/base/randu' );
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function rand( n ) {
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return n * randu();
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}
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var memoized = memoize( rand );
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var v1 = memoized( 5 );
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var v2 = memoized( 5 );
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var bool = ( v1 === v2 );
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// returns true
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```
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By default, the implementation serializes provided arguments as a `string` and stores results using the `string` as an identifier. To use a custom hash function, provide a hash function argument.
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```javascript
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function add( obj ) {
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return obj.x + obj.y + obj.z;
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}
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obj = {
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'x': 3,
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'y': 4,
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'z': 5
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};
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// Default behavior...
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var memoized = memoize( add );
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var v1 = memoized( obj );
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// returns 12
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var str = obj.toString();
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// returns '[object Object]'
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var v2 = memoized.cache[ str ];
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// returns 12
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obj.x = 1000;
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var v3 = memoized( obj );
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// returns 12
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// Custom hash function...
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function hashFunction( args ) {
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return JSON.stringify( args );
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}
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memoized = memoize( add, hashFunction );
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v1 = memoized( obj );
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// returns 1009
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str = hashFunction( [ obj ] );
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// returns '[{"x":1000,"y":4,"z":5}]'
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v2 = memoized.cache[ str ];
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// returns 1009
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obj.x = 6;
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v3 = memoized( obj );
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// returns 15
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```
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#### memoized.cache
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Results cache. Note that, while the property is **read-only**, cache contents may be modified independently of the memoized function.
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```javascript
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function beep( x ) {
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throw new Error( 'boop' );
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}
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var memoized = memoize( beep );
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var cache = memoized.cache;
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// returns {}
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// Modify the cache:
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cache[ 'bop' ] = 'bip';
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var str = memoized( 'bop' );
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// returns 'bip'
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```
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</section>
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<!-- /.usage -->
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<!-- Package usage notes. Make sure to keep an empty line after the `section` element and another before the `/section` close. -->
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<section class="notes">
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## Notes
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- The implementation does **not** set the `length` of the returned function. Accordingly, the returned function `length` is **always** `0`.
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- The evaluation context is **always** `null`.
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</section>
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<!-- /.notes -->
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<!-- Package usage examples. -->
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<section class="examples">
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## Examples
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<!-- eslint no-undef: "error" -->
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```javascript
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var randu = require( '@stdlib/random/base/randu' );
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var floor = require( '@stdlib/math/base/special/floor' );
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var memoize = require( '@stdlib/utils/memoize' );
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var fcn;
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var n;
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var v;
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var i;
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function rand( n ) {
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return n * randu();
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}
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fcn = memoize( rand );
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for ( i = 0; i < 100; i++ ) {
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n = floor( randu() * 5 );
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v = fcn( n );
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console.log( 'rand(%d) = %d', n, v );
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}
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```
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</section>
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<!-- /.examples -->
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<!-- Section to include cited references. If references are included, add a horizontal rule *before* the section. Make sure to keep an empty line after the `section` element and another before the `/section` close. -->
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<section class="references">
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</section>
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<!-- /.references -->
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<!-- Section for all links. Make sure to keep an empty line after the `section` element and another before the `/section` close. -->
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<section class="links">
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</section>
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<!-- /.links -->
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