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

possible duplicate of [How to add a new method to a php object on the fly?](http://stackoverflow.com/questions/2938004/how-to-add-a-new-method-to-a-php-object-on-the-fly) — mario, Dec 16 '11 at 18:16

score 3 · Accepted Answer · answered Dec 16 '11 at 18:13

3

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

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

$a->function_name = $sum;

answered Dec 16 '11 at 18:13

Eric

1,356
14
24

score 2 · Answer 2 · answered Dec 16 '11 at 18:09

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

?>

answered Dec 16 '11 at 18:09

Esailija

138,174
23
272
326

Cool! but i need that the function declaration and the the class initialization are in the same scope? – Zorb Dec 16 '11 at 18:12
@Zorb, what do you mean, sum is a public method of class A ? Can you edit your original question and put sum where it's supposed to be – Esailija Dec 16 '11 at 18:15
You're kind of misusing `call_user_func_array()` here ... if you know the parameters you should simply use `call_user_func()`, if not, you should do `$args = func_get_args(); call_user_func_array($this->function_name, $args);` instead of creating an array from the known parameters. – Dec 16 '11 at 18:17
@rdlowrey sure, don't know why it popped into my head first. Just wanted to get a fast answer out :P – Esailija Dec 16 '11 at 18:21
@Esailija i thinking about if the class cant see directly the function and i pass it the function can the class use it? now is clear , thanks! – Zorb Dec 16 '11 at 18:24
@Esailija haha lol on the speed thing. Gotta get 'em answered before the SO sharks start circling :) – Dec 16 '11 at 18:25

score 1 · Answer 3 · answered Dec 16 '11 at 18:11

It works regardless of scope. You just gotta call it using call_user_func. I also fixed a couple of typos in your example.

<?php
    class A {
        public $function_name;
        public function run($arg1, $arg2) {
        call_user_func($this->function_name, $arg1, $arg2);
        }
    }  

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

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

    $a->run(2, 3);
?>

Live example

score 0 · Answer 4 · answered Dec 16 '11 at 18:19

Another way is to make use variable variables (applicable to object method)

public static function sum($arg1, $arg2)
{
  ..
}

public function run($arg1, $arg2)
{
  $func = $this->function_name;
  $func( $arg1, $arg2);         <-- procedural call
  self::$func($arg1, $arg2);    <-- static method call
}

score 0 · Answer 5 · answered Dec 16 '11 at 18:22

Use any variation of the Callback pseudo type. Use it with call_user_func or call_user_func_array

The manual gives great examples of usage for the above.

Also see the new php 5.4 Closure::bindTO method if you want to be able to easily use the $this keyword in it.

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

5 Answers5