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

Community · Accepted Answer · 2023-11-17 20:08:53Z

3

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 in that case you should use one of these calls (these 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:

Classes have two main types of functions: static and non-static. In normal code, 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 function is always 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.

edited Nov 17, 2023 at 20:08

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answered Dec 30, 2009 at 9:12

Matijs

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3 Comments

Stick it to THE MAN Over a year ago

Your code is correct (I tried it). I still dont understand however, how my commented out line is equivalent to the line you wrote. I thought get_class($peer) would return the name of the peer class, as a string, which would then be appended to the '::retrieveByPK' string, to complete the method name. Please explain why get_class($peer) returns 'GeneralToolkit' - or did you make a mistake?

Stick it to THE MAN Over a year ago

As it turns out, this also works: return call_user_func(array(get_class($peer), 'retrieveByPK'), $comment->getItemId());

Peter Lindqvist Over a year ago

From your example we cannot be sure that get_class($peer) does return GeneralToolkit, but if you have symfony experience i guess it's possible to know that. If it's true, which is something i don't know.

Peter Lindqvist · Accepted Answer · 2009-12-30 09:28:16Z

3

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.

edited Dec 30, 2009 at 9:28

answered Dec 30, 2009 at 9:09

Peter Lindqvist

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3 Comments

Matijs Over a year ago

It is wrong. retrieveByPk is not a static function in the working example.

Stick it to THE MAN Over a year ago

Matjis is right, your code did not work, and the second solution you offered does not unfortunately, answer my original question.

Peter Lindqvist Over a year ago

Right, i misunderstood the question a bit. Updated my answer to reflect this.

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