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# ternaryOutputDataType

> Resolve the output ndarray [data type][@stdlib/ndarray/dtypes] for a ternary function.

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</section>

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## Usage

```javascript
var ternaryOutputDataType = require( '@stdlib/ndarray/base/ternary-output-dtype' );
```

#### ternaryOutputDataType( xdtype, ydtype, zdtype, policy )

Resolves the output ndarray [data type][@stdlib/ndarray/dtypes] for a ternary function according to a [data type policy][@stdlib/ndarray/output-dtype-policies].

```javascript
var dt = ternaryOutputDataType( 'int32', 'float32', 'float32', 'floating_point' );

var s = String( dt );
// returns 'float64'
```

The function supports the following parameters:

-   **xdtype**: first input ndarray [data type][@stdlib/ndarray/dtypes].
-   **ydtype**: second input ndarray [data type][@stdlib/ndarray/dtypes].
-   **zdtype**: third input ndarray [data type][@stdlib/ndarray/dtypes].
-   **policy**: output [data type policy][@stdlib/ndarray/output-dtype-policies].

If `policy` is a [data type][@stdlib/ndarray/dtypes], the function always returns the `policy` value (i.e., the third argument).

```javascript
var dt = ternaryOutputDataType( 'float32', 'float32', 'float32', 'float64' );

var s = String( dt );
// returns 'float64'

dt = ternaryOutputDataType( 'int32', 'int8', 'int32', 'float64' );

s = String( dt );
// returns 'float64'

// ...
```

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## Notes

-   The function **always** applies [type promotion][@stdlib/ndarray/promotion-rules] to the provided data types, except for the following [data type policies][@stdlib/ndarray/output-dtype-policies]:

    -   `default`
    -   `default_index`
    -   `same`
    -   `<dtype>`

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## Examples

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

```javascript
var naryFunction = require( '@stdlib/utils/nary-function' );
var unzip = require( '@stdlib/utils/unzip' );
var nCartesianProduct = require( '@stdlib/array/base/n-cartesian-product' );
var dtypes = require( '@stdlib/ndarray/dtypes' );
var logEachMap = require( '@stdlib/console/log-each-map' );
var ternaryOutputDataType = require( '@stdlib/ndarray/base/ternary-output-dtype' );

// Get the list of real-valued floating-point data types:
var dt = dtypes( 'real_floating_point' );

// Define a list of output data type policies:
var policies = [
    'default',
    'real',
    'floating_point',
    'complex_floating_point'
];

// Generate dtype-policy Cartesian products:
var args = nCartesianProduct( dt, dt, dt, policies );

// Unzip the argument pair array:
args = unzip( args );

// Resolve output data types:
logEachMap( 'dtypes: (%7s, %7s, %7s). policy: %-24s. output dtype: %s.', args[ 0 ], args[ 1 ], args[ 2 ], args[ 3 ], naryFunction( ternaryOutputDataType, 4 ) );
```

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</section>

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[@stdlib/ndarray/dtypes]: https://github.com/stdlib-js/ndarray/tree/main/dtypes

[@stdlib/ndarray/output-dtype-policies]: https://github.com/stdlib-js/ndarray/tree/main/output-dtype-policies

[@stdlib/ndarray/promotion-rules]: https://github.com/stdlib-js/ndarray/tree/main/promotion-rules

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