# Union Type Definition
A Union is an abstract type that simply enumerates other Object Types. 
The value of Union Type is actually a value of one of included Object Types.

In **graphql-php** union type is an instance of `GraphQL\Type\Definition\UnionType` 
(or one of its subclasses) which accepts configuration array in a constructor:

```php
<?php
use GraphQL\Type\Definition\UnionType;

$searchResultType = new UnionType([
    'name' => 'SearchResult',
    'types' => [
        MyTypes::story(),
        MyTypes::user()
    ],
    'resolveType' => function($value) {
        if ($value->type === 'story') {
            return MyTypes::story();            
        } else {
            return MyTypes::user();
        }
    }
]);
```

This example uses **inline** style for Union definition, but you can also use  
[inheritance or type language](index.md#type-definition-styles).

# Configuration options
The constructor of UnionType accepts an array. Below is a full list of allowed options:

Option | Type | Notes
------ | ---- | -----
name | `string` | **Required.** Unique name of this interface type within Schema
types | `array` | **Required.** List of Object Types included in this Union. Note that you can't create a Union type out of Interfaces or other Unions.
description | `string` | Plain-text description of this type for clients (e.g. used by [GraphiQL](https://github.com/graphql/graphiql) for auto-generated documentation)
resolveType | `callback` | **function($value, $context, [ResolveInfo](../reference.md#graphqltypedefinitionresolveinfo) $info)**<br> Receives **$value** from resolver of the parent field and returns concrete Object Type for this **$value**.