Question

class A
{
    static $v = "A";

    static function echoExtendedStaticVariable() {
        echo self::$v;
    }
}

class B extends A
{
    static $v = "B";
    // override A's variable with "B"
}

Why does:

echo B::$v

print “A”?

And how do I get it to print “B”?

Is there a way to do this before PHP 5.3?

Answer 1

B->echoExtendedStaticVariable() == 'A' because self:: is evaluated at compile-time, not run-time. It’s as if you wrote A:: instead of self::.

What you want is a feature called “late static binding”–it’s “late” because it can determine the class at runtime instead of at compile-time.

You can emulate this (sort-of) in PHP 5.2 using ReflectionClass:

class A
{
    static $v = "A";
    function echoExtendedStaticVariable() {
        $rc = new ReflectionClass($this);
        echo $rc->getStaticPropertyValue('v');
    }
}
class B extends A
{
    static $v = "B";
}
$b = new B();
$b->echoExtendedStaticVariable(); // B

Note that you can only do this if you have access to an instance, so you can’t make echoExtendedStaticVariable a static method and expect this to work.