Question

I’m trying to implement what I believe is a factory class. I have an API framework. After my front controller has processed the request it attempts to return the output to the client. The call in my front controller looks like this:

<?php
...
$response_obj = new Response($response_str, 'json');
echo $response_obj->render();
?>

My Response class basically takes the second argument as the type of class to instantiate, and passes this new class the contents of $response_str. Here it is:

<?php
class Response {

    public function __construct($data, $format) {
        switch ($format) {
            case 'json':
                $obj = new ResponseJson($data);
            break;
        }
        return $obj;
    }
}

And then my ResponseJson class looks as follows:

<?php
class ResponseJson {

    protected $data;

    public function __construct($data) {
        $this->data = $data;
        return $this;
    }

    public function render() {
        header('Content-Type: application/json');
        return json_encode($this->data);
    }
}

However, in my front controller $response_obj returns its type as Response and not ResponseJson as would be expected, and a call to the render() method (which exists in ResponseJson and not Response) throws a Fatal error:

Fatal error: Call to undefined method Response::render() in /Users/Martin/Sites/api-framework/index.php on line 61

Where am I going wrong?

Answer 1

what you describe is not a factory, but rather invalid code. (the __construct will always return a new instance of the class it is implemented in. in fact, it does not need to return anything because this has no effect!)

A factory is usually implemented as a static function that can be called without instantiating an object of the factory class. It then creates an object instance of a class (in most cases of another class, as in your case) and returns that.

your Response class should look like this:

<?php
class Response {

    static public function create($data, $format) {
        switch ($format) {
            case 'json':
                $obj = new ResponseJson($data);
                break;
            case default:
                return NULL; // or throw exception!
                break;
        }
        return $obj;
    }
}

and your frontend controller like this:

<?php
...
$response_obj = Response::create($response_str, 'json');
echo $response_obj->render();
?>