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Type Juggling> <Callbacks
[edit] Last updated: Sat, 12 May 2012

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Pseudo-types and variables used in this documentation


mixed indicates that a parameter may accept multiple (but not necessarily all) types.

gettype() for example will accept all PHP types, while str_replace() will accept strings and arrays.


number indicates that a parameter can be either integer or float.


callback pseudo-types was used in this documentation before callable type hint was introduced by PHP 5.4. It means exactly the same.


void as a return type means that the return value is useless. void in a parameter list means that the function doesn't accept any parameters.


$... in function prototypes means and so on. This variable name is used when a function can take an endless number of arguments.

Type Juggling> <Callbacks
[edit] Last updated: Sat, 12 May 2012
add a note add a note User Contributed Notes Pseudo-types and variables used in this documentation
liam at helios-sites dot com 06-Dec-2010 04:44
Note that (e.g.) usort calls on static methods of classes in a namespace need to be laid out as follows:

usort($arr, array('\Namespace\ClassName', 'functionName'));
michael dot martinek at gmail dot com 29-Aug-2009 09:20
The documentation is a little confusing, and with the recent OO changes it adds a little more to the confusion.

I was curious whether you could pass an object through the user func, modify it in that callback and have the actual object updated or whether some cloning was going on behind the scenes.

class Test
$sValue = 'abc';

$objTest->sValue = '123';

$obj = new Test();

call_user_func(array($obj, 'testing'), $obj);



This works as expected: The object is not cloned, and $sValue is properly set to '123'. With the OO changes in PHP 5, you don't need to do "function testing(&$objTest)" as it is already passed by reference.
phpguy at lifetoward dot com 11-Jun-2009 05:44
I noticed two important thing about putting callbacks into an arg list when calling a function:

1. The function to which the callback refers must be defined earlier in the source stream. So for example:

function main() {...; usort($array, 'sortfunction'); ... }
function sortfunction($a, $b){ return 0; }

Will NOT work, but this will:

function sortfunction($a, $b){ return 0; }
function main() {...; usort($array, 'sortfunction'); ... }

2. It's not really just a string. For example, this doesn't work:

usort($array, ($reverse?'reversesorter':'forwardsorter'));

I found these two discoveries quite counterintuitive.
sahid dot ferdjaoui at gmail dot com 20-Apr-2009 03:19
An example with PHP 5.3 and lambda functions


(function ($value) {
    return new
MyFormElement ($value);

Hayley Watson 23-May-2007 10:44
The mixed pseudotype is explained as meaning "multiple but not necessarily all" types, and the example of str_replace(mixed, mixed, mixed) is given where "mixed" means "string or array".
Keep in mind that this refers to the types of the function's arguments _after_ any type juggling.
levi at alliancesoftware dot com dot au 08-Feb-2007 02:44
Parent methods for callbacks should be called 'parent::method', so if you wish to call a non-static parent method via a callback, you should use a callback of
// always works
$callback = array($this, 'parent::method')

// works but gives an error in PHP5 with E_STRICT if the parent method is not static
$callback array('parent', 'method');
Edward 01-Feb-2007 02:15
To recap mr dot lilov at gmail dot com's comment: If you want to pass a function as an argument to another function, for example "array_map", do this:

regular functions:
(intval, $array)

static functions in a class:
(array('MyClass', 'MyFunction'), $array)

functions from an object:
(array($this, 'MyFunction'), $array)

I hope this clarifies things a little bit

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