Abstract constants in PHP - Force a child class to define a constant

Question

I noticed that you can\'t have abstract constants in PHP.

Is there a way I can force a child class to define a constant (which I need to use in one of the abstract c

Answer 1

Unfortunately not... a constant is exactly what it says on the tin, constant. Once defined it can't be redefined, so in that way, it is impossible to require its definition through PHP's abstract inheritance or interfaces.

However... you could check to see if the constant is defined in the parent class's constructor. If it doesn't, throw an Exception.

abstract class A
{
    public function __construct()
    {
        if (!defined('static::BLAH'))
        {
            throw new Exception('Constant BLAH is not defined on subclass ' . get_class($this));
        }
    }
}

class B extends A
{
    const BLAH = 'here';
}

$b = new B();

This is the best way I can think of doing this from your initial description.