How to override a class constant in PHP?

Question

When working with constants, I've always tried to define constants like the following which allows end-users to override their values.

if ( ! defined( 'MY_CONST' ) )
    define ( 'MY_CONST', 10 );

I've now started to work with classes (OOP) and would like to know if there's a way to define a class constant that will allow the value to be overridden by end-users?

Refs:

• http://php.net/manual/en/function.define.php
• http://php.net/manual/en/language.oop5.constants.php

Answer 1

If your users are extending your class, they can redefine the constant just fine:

class Foo extends Bar {
    const BAZ = 42;
}

It doesn't matter whether Bar already defines a BAZ constant or not. All you have to do in your code is make sure you're referring to the "current classes" constant using late static binding:

public function useConst() {
    echo static::BAZ;
}

Otherwise, you have the option of doing this:

if (!defined('BAZ')) {
    define('BAZ', 42);
}

class Bar {
    const BAZ = BAZ;
}

That's not really very elegant though. You should rather be using getters and setters on your class to allow configuration, rather than using constants for this purpose:

Bar::setBaz(42);