@stdlib/strided/base/nullary-addon-dispatch/README.md

Strided.

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# dispatch

> Dispatch to a native add-on applying a nullary function.

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## Usage

```javascript
var dispatch = require( '@stdlib/strided/base/nullary-addon-dispatch' );
```

#### dispatch( addon, fallback )

Returns a function which dispatches to a native add-on applying a nullary function.

```javascript
function addon( N, dtypeX, x, strideX ) {
    // Call into native add-on...
}

function fallback( N, dtypeX, x, strideX ) {
    // Fallback JavaScript implementation...
}

// Create a dispatch function:
var f = dispatch( addon, fallback );

// ...

// Invoke the dispatch function with strided array arguments:
f( 2, 'generic', [ 1, 2 ], 1 );
```

The returned function has the following signature:

```text
f( N, dtypeX, x, strideX )
```

where

-   **N**: number of indexed elements.
-   **dtypeX**: `x` data type.
-   **x**: output array.
-   **strideX**: `x` stride length.

The `addon` function should have the following signature:

```text
f( N, dtypeX, x, strideX )
```

where

-   **N**: number of indexed elements.
-   **dtypeX**: `x` data type (enumeration constant).
-   **x**: output array.
-   **strideX**: `x` stride length.

The `fallback` function should have the following signature:

```text
f( N, dtypeX, x, strideX )
```

where

-   **N**: number of indexed elements.
-   **dtypeX**: `x` data type.
-   **x**: output array.
-   **strideX**: `x` stride length.

#### dispatch.ndarray( addon, fallback )

Returns a function which dispatches to a native add-on applying a nullary function using alternative indexing semantics.

<!-- eslint-disable max-len -->

```javascript
function addon( N, dtypeX, x, strideX ) {
    // Call into native add-on...
}

function fallback( N, dtypeX, x, strideX, offsetX ) {
    // Fallback JavaScript implementation...
}

// Create a dispatch function:
var f = dispatch.ndarray( addon, fallback );

// ...

// Invoke the dispatch function with strided array arguments:
f( 2, 'generic', [ 1, 2 ], 1, 0 );
```

The returned function has the following signature:

```text
f( N, dtypeX, x, strideX, offsetX )
```

where

-   **N**: number of indexed elements.
-   **dtypeX**: `x` data type.
-   **x**: output array.
-   **strideX**: `x` stride length.
-   **offsetX**: starting `x` index.

The `addon` function should have the following signature:

```text
f( N, dtypeX, x, strideX )
```

where

-   **N**: number of indexed elements.
-   **dtypeX**: `x` data type (enumeration constant).
-   **x**: output array.
-   **strideX**: `x` stride length.

The `fallback` function should have the following signature:

```text
f( N, dtypeX, x, strideX, offsetX )
```

where

-   **N**: number of indexed elements.
-   **dtypeX**: `x` data type.
-   **x**: output array.
-   **strideX**: `x` stride length.
-   **offsetX**: starting `x` index.

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## Notes

-   To determine whether to dispatch to the `addon` function, the returned dispatch function checks whether the provided arrays are typed arrays. If the provided arrays are typed arrays, the dispatch function invokes the `addon` function; otherwise, the dispatch function invokes the `fallback` function.

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## Examples

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<!-- eslint no-undef: "error" -->

```javascript
var Float64Array = require( '@stdlib/array/float64' );
var dispatch = require( '@stdlib/strided/base/nullary-addon-dispatch' );

function addon( N, dtypeX, x, strideX ) {
    console.log( x );
    // => <Float64Array>[ 3, 4 ]
}

function fallback( N, dtypeX, x, strideX, offsetX ) {
    console.log( x );
    // => [ 1, 2, 3, 4 ]
}

// Create a dispatch function:
var f = dispatch.ndarray( addon, fallback );

// Create a strided array:
var x = new Float64Array( [ 1, 2, 3, 4 ] );

// Dispatch to the add-on function:
f( 2, 'float64', x, 1, 2 );

// Define a new strided array:
x = [ 1, 2, 3, 4 ];

// Dispatch to the fallback function:
f( 2, 'generic', x, 1, 2 );
```

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