GraphQL\Type\Definition\FieldDefinition::create PHP Метод

    public static function create($field, $typeName = null)
    {
        if ($typeName) {
            Config::validateField($typeName, $field, self::getDefinition());
        }
        return new self($field);
    }

 public static function typeNameMetaFieldDef()
 {
     if (!isset(self::$map['__typename'])) {
         self::$map['__typename'] = FieldDefinition::create(['name' => '__typename', 'type' => Type::nonNull(Type::string()), 'description' => 'The name of the current Object type at runtime.', 'args' => [], 'resolve' => function ($source, $args, $context, ResolveInfo $info) {
             return $info->parentType->name;
         }]);
     }
     return self::$map['__typename'];
 }