Using call_user_func() with objects

Question

The following two statements should be identical, yet the commented out statement does not work. Can anyone explain ?

$peer = GeneralToolkit::getPeerModel($model);
//return call_user_func(get_class($peer).'::retrieveByPK',array($comment->getItemId()));
return $peer->retrieveByPK($comment->getItemId());

PS: I am using PHP 5.2.11

Answer 1

return call_user_func(
    array($peer,'retrieveByPK'),
    $comment->getItemId()
);

is the equivalent of

return $peer->retrieveByPK($comment->getItemId());

The first argument gives an object reference, and a function name. The second argument gives the arguments passed to the function that is being called.

The :: syntax is used to reference static methods and properties of a class. Which is different from referencing non-static methods and properties.

Answer 2

The two calls are not the same. You are calling:

return GeneralToolkit::retrieveByPK(array($comment->getItemId());

So of course you get a different answer. This is the correct code:

return call_user_func(array($peer, 'retrieveByPK'), $comment->getItemId());

Unless 'retrieveByPK' is static but then you should use one of these calls (that all do the same thing):

return call_user_func(
    get_class($peer) . '::retrieveByPK', 
    $comment->getItemId());

return call_user_func(
    array(get_class($peer), 'retrieveByPK'), 
    $comment->getItemId());

return call_user_func_array(
    get_class($peer) . '::retrieveByPK', 
    array($comment->getItemId()));

return call_user_func_array(
    array(get_class($peer), 'retrieveByPK'), 
    array($comment->getItemId()));

So in that case your error was in using array() while calling call_user_func() instead of call_user_func_array().

Explanation added

Classes have two main types of functions static and non-static. In normal code non static functions are called using ClassName::functionName(). For non-static functions you need first to create an object using $objectInstance = new ClassName(), then call the function using $objectInstance->functionName().

When using callbacks you also make a distinction between static and non-static functions. Static functions are stored as either a string "ClassName::functionName" or an array containing two strings array("ClassName", "FunctionName"). A callback on a non static functions always is an array containing the object to call and the function name as a string: array($objectInstance, "functionName).

See the PHP Callback documentation for more details.