NULL
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.
Pseudo-types and variables used in this documentation
mixed
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.
callback
Some functions like call_user_func() or usort() accept user-defined callback functions as a parameter. Callback functions can not only be simple functions, but also object methods, including static class methods.
A PHP function is passed by its name as a string. Any built-in or user-defined function can be used, except language constructs such as: array(), echo(), empty(), eval(), exit(), isset(), list(), print() or unset().
A method of an instantiated object is passed as an array containing an object at index 0 and the method name at index 1.
Static class methods can also be passed without instantiating an object of that class by passing the class name instead of an object at index 0.
Apart from common user-defined function, create_function() can also be used to create an anonymous callback function.
Exemple #1 Callback function examples
<?php
// An example callback function
function my_callback_function() {
echo 'hello world!';
}
// An example callback method
class MyClass {
static function myCallbackMethod() {
echo 'Hello World!';
}
}
// Type 1: Simple callback
call_user_func('my_callback_function');
// Type 2: Static class method call
call_user_func(array('MyClass', 'myCallbackMethod'));
// Type 3: Object method call
$obj = new MyClass();
call_user_func(array($obj, 'myCallbackMethod'));
// Type 4: Static class method call (As of PHP 5.2.3)
call_user_func('MyClass::myCallbackMethod');
// Type 5: Relative static class method call (As of PHP 5.3.0)
class A {
public static function who() {
echo "A\n";
}
}
class B extends A {
public static function who() {
echo "B\n";
}
}
call_user_func(array('B', 'parent::who')); // A
?>
Note: In PHP4, it was necessary to use a reference to create a callback that points to the actual object, and not a copy of it. For more details, see References Explained.
void
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.
add a note
User Contributed NotesPseudo-types and variables used in this documentation
Hayley Watson
24-May-2007 07:44
24-May-2007 07:44
levi at alliancesoftware dot com dot au
08-Feb-2007 11:44
08-Feb-2007 11:44
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 11:15
01-Feb-2007 11:15
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:
<?
array_map(intval, $array)
?>
static functions in a class:
<?
array_map(array('MyClass', 'MyFunction'), $array)
?>
functions from an object:
<?
array_map(array($this, 'MyFunction'), $array)
?>
I hope this clarifies things a little bit