# unaryInputCastingDataType
> Resolve the input ndarray casting [data type][@stdlib/ndarray/dtypes] for a unary function.
## Usage
```javascript
var unaryInputCastingDataType = require( '@stdlib/ndarray/base/unary-input-casting-dtype' );
```
#### unaryInputCastingDataType( idtype, odtype, policy )
Resolves the input ndarray casting [data type][@stdlib/ndarray/dtypes] for a unary function according to a [data type policy][@stdlib/ndarray/input-casting-policies].
```javascript
var dt = unaryInputCastingDataType( 'int32', 'float64', 'promoted' );
// returns 'float64'
```
The function supports the following parameters:
- **idtype**: input ndarray data type.
- **odtype**: output ndarray data type.
- **policy**: input ndarray [casting policy][@stdlib/ndarray/input-casting-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 = unaryInputCastingDataType( 'float32', 'float64', 'complex128' );
// returns 'complex128'
dt = unaryInputCastingDataType( 'int32', 'float64', 'complex128' );
// returns 'complex128'
// ...
```
## Examples
```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 inputCastingDataType = require( '@stdlib/ndarray/base/unary-input-casting-dtype' );
// Get the list of real-valued data types:
var dt = dtypes( 'real' );
// Define a list of casting policies:
var policies = [
'none',
'promoted',
'accumulation',
'output'
];
// Generate dtype-policy argument groups:
var args = nCartesianProduct( dt, dt, policies );
// Unzip the argument arrays:
args = unzip( args );
// Resolve casting data types:
logEachMap( 'dtypes: (%10s, %10s). policy: %20s. result: %10s.', args[ 0 ], args[ 1 ], args[ 2 ], naryFunction( inputCastingDataType, 3 ) );
```
[@stdlib/ndarray/dtypes]: https://github.com/stdlib-js/ndarray/tree/main/dtypes
[@stdlib/ndarray/input-casting-policies]: https://github.com/stdlib-js/ndarray/tree/main/input-casting-policies