Class inheritance in PHP 5.2: Overriding static variable in extension class?

Question

I need to bea be able to use a static variable set in a class that extends a base class... from the base class.

Consider this:

class Animal {
    public          


        

Answer 1

I ran into this problem when subclassing something in the Zend Framework. My determination was that in purely static land, you only have one option... Redefine the function in the inheriting class:

class Animal {
    public static $color = 'black';

    public static function get_color()
    {
        return self::$color;
    }
}

class Dog extends Animal {
    public static $color = 'brown';

    public static function get_color() 
    {
      return self::$color;
    }
}

If you are able to create instances - You can use get_class($this) to find out the calling class, for example:

class Animal {
    public static $color = 'black';

    public function getColor() // note, not static
    {
      $class = get_class($this);
      return $class::$color;
    }
}

class Dog extends Animal {
    public static $color = 'brown';
}

$animal = new Animal();
echo $animal->getColor(); // prints 'black'
$dog = new Dog();
echo $dog->getColor(); // prints 'brown'

The only other option I thought of was using a function parameter to the static function to define a class it was being called from. It can default to __CLASS__ and then you can return parent::get_class($class) from the subclass. A pattern like this could be used to make re-using the static function easier (as I doubt returning a public static property is the only thing you are trying to use self:: for in that static method:

class Animal {
    public static $color = 'black';

    public static function get_color($class = __CLASS__)
    {
        // Super Simple Example Case... I imagine this function to be more complicated
        return $class::$color;
    }
}

class Dog extends Animal {
    public static $color = 'brown';

    public static function get_color($class = __CLASS__)
    {
      return parent::get_color($class);
    }
}

Answer 2

In PHP 5.3+, the following would be preferred:

class Animal {
    public static $color = 'black';

    public static function get_color()
    {
        return static::$color; // Here comes Late Static Bindings
    }
}

class Dog extends Animal {
    public static $color = 'brown';
}

echo Animal::get_color(); // prints 'black'
echo Dog::get_color(); // prints 'brown'

Late Static Bindings (PHP.net)

Answer 3

Sadly, before PHP 5.3 there's no way to simulate late static binding. The only way you can get the inheritance to work as you intend is if those are instance variables and methods.