# dispatch
> Dispatch to a native add-on applying a unary function to an input ndarray.
## Usage
```javascript
var dispatch = require( '@stdlib/ndarray/base/unary-addon-dispatch' );
```
#### dispatch( addon, fallback )
Returns a function which dispatches to a native add-on applying a unary function to an input ndarray.
```javascript
var array = require( '@stdlib/ndarray/array' );
var zeros = require( '@stdlib/ndarray/zeros' );
var dispatch = require( '@stdlib/ndarray/base/unary-addon-dispatch' );
function addon( x, metaX, y, metaY ) {
// Call into native add-on...
}
function fallback( x, y ) {
// Fallback JavaScript implementation...
}
// Create a dispatch function:
var f = dispatch( addon, fallback );
// ...
// Invoke the dispatch function with ndarray arguments:
var x = array( [ [ 1, 2], [ 3, 4 ] ] );
var y = zeros( [ 2, 2 ] );
f( x, y );
```
The returned function has the following signature:
```text
f( x, y )
```
where
- **x**: input ndarray.
- **y**: output ndarray.
The `addon` function should have the following signature:
```text
f( xbuf, metaX, ybuf, metaY )
```
where
- **xbuf**: input ndarray data buffer.
- **metaX**: [serialized][@stdlib/ndarray/base/serialize-meta-data] input ndarray meta data.
- **ybuf**: output ndarray data buffer.
- **metaY**: [serialized][@stdlib/ndarray/base/serialize-meta-data] output ndarray meta data.
The `fallback` function should have the following signature:
```text
f( x, y )
```
where
- **x**: input ndarray.
- **y**: output ndarray.
## Notes
- To determine whether to dispatch to the `addon` function, the returned dispatch function checks whether the underlying ndarray data buffers are typed arrays. If the data buffers are typed arrays, the dispatch function invokes the `addon` function; otherwise, the dispatch function invokes the `fallback` function.
## Examples
```javascript
var array = require( '@stdlib/ndarray/array' );
var zeros = require( '@stdlib/ndarray/zeros' );
var ndarray2array = require( '@stdlib/ndarray/to-array' );
var dispatch = require( '@stdlib/ndarray/base/unary-addon-dispatch' );
function addon( xbuf, metaX, ybuf, metaY ) {
console.log( xbuf );
// => [ 1, 2, 3, 4 ]
console.log( ybuf );
// => [ 0, 0, 0, 0 ]
}
function fallback( x, y ) {
console.log( ndarray2array( x ) );
// => [ [ 1, 2 ], [ 3, 4 ] ]
console.log( ndarray2array( y ) );
// => [ [ 0, 0 ], [ 0, 0 ] ]
}
// Create a dispatch function:
var f = dispatch( addon, fallback );
// Create ndarrays:
var opts = {
'dtype': 'float64',
'casting': 'unsafe'
};
var x = array( [ [ 1, 2 ], [ 3, 4 ] ], opts );
var y = zeros( [ 2, 2 ], opts );
// Dispatch to the add-on function:
f( x, y );
// Define new ndarrays:
opts = {
'dtype': 'generic'
};
x = array( [ [ 1, 2 ], [ 3, 4 ] ], opts );
y = zeros( [ 2, 2 ], opts );
// Dispatch to the fallback function:
f( x, y );
```
[@stdlib/ndarray/base/serialize-meta-data]: https://github.com/stdlib-js/ndarray/tree/main/base/serialize-meta-data