PHP: constant as variable in function

Question

I'm trying to use constant as a function paramter, is it possible to check type of this constant.

Example of what I want:

class ApiError {
  const INVALID_REQUEST = 200;
}

class Response {
  public function status(ApiError $status) {
    //function code here
  }
}

USE:

$response = new Response();
$response->status(ApiError::INVALID_REQUEST);

This shoud check that given $status is constant of class ApiError. Is something like this possible?

Answer 1

As the others mentioned, there is no generic solution. But if you'd like to do it in a very clean way, model every "object" that you're dealing with (= every possible status), e.g.:

interface ApiError {   // make it an abstract class if you need to add logic
    public function getCode();
}

class InvalidRequestApiError implements ApiError {
    public function getCode() {
        return 200;
    }
}

// Usage:
$response = new Response();
$response->status( new InvalidRequestApiError() );

class Response {
    public function status(ApiError $status) {
        echo "API status: " . $status->getCode();
    }
    // ...
}

This leaves you with a lot of classes, because you encapsulate simple numbers, but also with the ability to type-hint.

Answer 2

You can use in_array() to test against whitelisted values, which is a recommended strategy whenever you need to validate input to a specific value set:

// Test if it is in an array of valid status constants...
$valid_statuses = array(
   ApiError::INVALID_REQUEST, 
   ApiError::INVALID_SOMETHINGELSE, 
   ApiError::STATUS_OK
);
if (in_array($status, $valid_statuses)) {
   // it's an acceptable value
}

To whitelist all constants of a class, you could use reflection and retrieve the constants from ApiError via ReflectionClass::getconstants()

$refl = new ReflectionClass('ApiError');
$valid_statuses = $refl->constants();