Pass a function by reference in PHP

Question

For what it's worth, how about giving something like this a shot? (Yes, I know it's an anonymous function which was mentioned in the post, but I was disgruntled at the abundance of replies that did not mention closures/function-objects at all so this is mostly a note for people running across this post.)

I don't use PHP, but using a closure appears to work in PHP 5.3 (but not PHP 5.2) as demonstrated here. I am not sure what the limitations, if any, there are. (For all I know the closure will eat your children. You have been warned.)

function doIt ($fn) {
  echo "doIt\n";
  return $fn();
}

function doMe () {
  echo "doMe\n";
}

// I am using a closure here.
// There may be a more clever way to "get the function-object" representing a given
// named function, but I do not know what it is. Again, I *don't use PHP* :-)
echo doIt(function () { doMe(); });

Happy coding.

The problem with call_user_func() is that you're passing the return value of the function called, not the function itself.

I've run into this problem before too and here's the solution I came up with.

function funcRef($func){
  return create_function('', "return call_user_func_array('{$func}', func_get_args());");
}

function foo($a, $b, $c){
    return sprintf("A:%s B:%s C:%s", $a, $b, $c);
}

$b = funcRef("foo");

echo $b("hello", "world", 123);

//=> A:hello B:world C:123

ideone.com demo

No, functions are not first class values in PHP, they cannot be passed by their name literal (which is what you're asking for). Even anonymous functions or functions created via create_function are passed by an object or string reference.

You can pass a name of a function as string, the name of an object method as (object, string) array or an anonymous function as object. None of these pass pointers or references, they just pass on the name of the function. All of these methods are known as the callback pseudo-type: http://php.net/callback

function func1(){
    echo 'echo1 ';
    return 'return1';
}

function func2($func){
    echo 'echo2 ' . $func();
}

func2('func1');

Result:

echo1 echo2 return1

In PHP 5.4.4 (haven't tested lower or other versions), you can do exactly as you suggested.

Take this as an example:

function test ($func) {
    $func('moo');
}

function aFunctionToPass ($str) {
    echo $str;
}

test('aFunctionToPass');

The script will echo "moo" as if you called "aFunctionToPass" directly.

A similar pattern of this Javascript first class function:

function add(first, second, callback){
    console.log(first+second);
    if (callback) callback();
}

function logDone(){
    console.log('done');
}

function logDoneAgain(){
    console.log('done Again');
}
add(2,3, logDone);
add(3,5, logDoneAgain);

Can be done in PHP (Tested with 5.5.9-1ubuntu on C9 IDE) in the following way:

// first class function
$add = function($first, $second, $callback) {
  echo "\n\n". $first+$second . "\n\n";
  if ($callback) $callback();
};

function logDone(){
  echo "\n\n done \n\n";
}
call_user_func_array($add, array(2, 3, logDone));
call_user_func_array($add, array(3, 6, function(){
  echo "\n\n done executing an anonymous function!";
}));

Result: 5 done 9 done executing an anonymous function!

Reference: https://github.com/zenithtekla/unitycloud/commit/873659c46c10c1fe5312f5cde55490490191e168