it is possible to assign a function to a class variable at runtime in php?

Question

it is possible to assign to a class variable a function at runtime to be executed? a kind of "function pointer" like C

something like this: (this won't work because sum is out of the scope of A, but this is the pattern i mean)

 class A {
    public $function_name;
    public functon run($arg1,$arg2){
        $function_name($arg1,$arg2);
    }
}  

function sum($a,$b){
    echo $a+$b;
}

$a=new A();
$a->function_name='sum';

$a->run();     

[edit] i know there is "call_user_func" but it need as i understand to have the function in the scope or use a public class method

Answer 1

You could use an anonymous function if you use PHP >5.3.0:

$sum = function($a, $b) {
    return $a+$b;
}

$a->function_name = $sum;

Answer 2

Using call_user_func_array:

<?php
class A {

    public $function_name;

    public function run($arg1,$arg2){

        return call_user_func_array( $this->function_name, array($arg1, $arg2 ) );

    }
}  

function sum($a,$b){
    return $a+$b;
}

$a=new A();
$a->function_name= 'sum';

var_dump( $a->run(1,1) ); //2

?>