php - Access a static variable by $var::$reference

Question

I am trying to access a static variable within a class by using a variable class name. I'm aware that in order to access a function within the class, you use call_user_func():

class foo {
    function bar() { echo 'hi'; }
} 
$class = 'foo';
call_user_func(array($class, 'bar')); // prints hi

However, this does not work when trying to access a static variable within the class:

class foo {
    public static $bar = 'hi';
} 
$class = "foo";
call_user_func(array($class, 'bar')); // nothing
echo $foo::$bar; // invalid

How do I get at this variable? Is it even possible? I have a bad feeling this is only available in PHP 5.3 going forward and I'm running PHP 5.2.6.

Answer 1

I think there is much better (more elegant) way then creating ReflectionClass instance. I also edited this code (and my answer) after few comments. I added example for protected variables (you can't of course access them from outside the class, so I made static getter and call it using variable pattern as well). You can use it in few different ways:

class Demo
{
    public static $foo = 42;
    protected static $boo = 43;
    public static function getProtected($name) {
        return self::$$name;
    }
}

$var1 = 'foo';
$var2 = 'boo';
$class = 'Demo';
$func = 'getProtected';
var_dump(Demo::$$var1);
var_dump($class::$foo);
var_dump($class::$$var1);
//var_dump(Demo::$$var2); // Fatal error: Cannot access protected property Demo::$boo
var_dump(Demo::getProtected($var2));
var_dump($class::getProtected($var2));
var_dump($class::$func($var2));

Documentation is here:

http://php.net/manual/en/language.variables.variable.php