119 lines
2.1 KiB
Markdown
119 lines
2.1 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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# Constant Function
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> Constant function.
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<section class="intro">
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A [constant function][constant-function] is a `function` whose output value is the same for every input value.
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</section>
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<!-- /.intro -->
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<section class="usage">
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## Usage
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```javascript
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var constantFunction = require( '@stdlib/utils/constant-function' );
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```
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#### constantFunction( x )
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Returns a [constant function][constant-function] which always returns `x`.
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```javascript
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var fcn = constantFunction( 'beep' );
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// returns <Function>
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var v = fcn();
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// returns 'beep'
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v = fcn();
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// returns 'beep'
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```
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</section>
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<!-- /.usage -->
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<section class="notes">
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## Notes
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- When provided an object reference, the returned `function` always returns the same reference.
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```javascript
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var obj = {};
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var fcn = constantFunction( obj );
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var bool = ( fcn() === obj );
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// returns true
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```
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</section>
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<!-- /.notes -->
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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 constantFunction = require( '@stdlib/utils/constant-function' );
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var bool;
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var fcn;
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var arr;
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var v;
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var i;
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fcn = constantFunction( 3.14 );
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for ( i = 0; i < 10; i++ ) {
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v = fcn();
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// returns 3.14
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}
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arr = [ 1, 2, 3 ];
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fcn = constantFunction( arr );
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for ( i = 0; i < 10; i++ ) {
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v = fcn();
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bool = ( v === arr );
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// returns true
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}
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```
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</section>
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<!-- /.examples -->
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<section class="links">
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[constant-function]: https://en.wikipedia.org/wiki/Constant_function
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</section>
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<!-- /.links -->
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