Php callback using this
Callback-функции могут быть обозначены объявлением типа callable .
Некоторые функции, такие как call_user_func() или usort() , принимают определённые пользователем callback-функции в качестве параметра. Callback-функции могут быть как простыми функциями, так и методами объектов, включая статические методы классов.
Передача
В PHP функции передаются по имени в виде строки. Можно использовать любые встроенные, либо созданные пользователем функции, за исключением конструкций языка, таких как: array() , echo , empty() , eval() , exit() , isset() , list() , print или unset() .
Метод созданного объекта ( object ) передаётся как массив, содержащий объект по индексу 0 и имя метода по индексу 1. Доступ к закрытым и защищённым методам разрешён изнутри класса.
Статические методы класса также могут быть вызваны без создания экземпляра объекта класса путём передачи имени класса вместо объекта в элементе массива с индексом 0 или выполнения ‘ClassName::methodName’ .
Помимо обычных пользовательских функций, в качестве callback-функции можно передавать анонимные функции и стрелочные функции.
Замечание:
Начиная с PHP 8.1.0, у Callback-функций как объектов первого класса та же семантика, что и у этого метода.
Как правило, любой объект, реализующий __invoke(), также может быть передан в параметр callback.
Пример #1 Пример callback-функции
// Пример callback-функции
function my_callback_function () echo ‘Привет, мир!’ ;
>
// Пример callback-метода
class MyClass static function myCallbackMethod () echo ‘Привет, мир!’ ;
>
>
// Тип 1: Простой callback
call_user_func ( ‘my_callback_function’ );
// Тип 2: Вызов статического метода класса
call_user_func (array( ‘MyClass’ , ‘myCallbackMethod’ ));
// Тип 3: Вызов метода класса
$obj = new MyClass ();
call_user_func (array( $obj , ‘myCallbackMethod’ ));
// Тип 4: Вызов статического метода класса
call_user_func ( ‘MyClass::myCallbackMethod’ );
// Тип 5: Вызов относительного статического метода
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
// Тип 6: Объекты, реализующие __invoke, могут быть использованы как callback
class C public function __invoke ( $name ) echo ‘Привет ‘ , $name , «\n» ;
>
>
$c = new C ();
call_user_func ( $c , ‘PHP!’ );
?>
Пример #2 Пример callback-функции с использованием замыкания
// Наше замыкание
$double = function( $a ) return $a * 2 ;
>;
// Диапазон чисел
$numbers = range ( 1 , 5 );
// Использование замыкания в качестве callback-функции
// для удвоения каждого элемента в нашем диапазоне
$new_numbers = array_map ( $double , $numbers );
print implode ( ‘ ‘ , $new_numbers );
?>
Результат выполнения данного примера:
Замечание:
Callback-функции, зарегистрированные такими функциями как call_user_func() и call_user_func_array() , не будут вызваны при наличии не пойманного исключения, брошенного в предыдущей callback-функции.
User Contributed Notes 18 notes
You can also use the $this variable to specify a callback:
public $property = ‘Hello World!’ ;
public function MyMethod ()
<
call_user_func (array( $this , ‘myCallbackMethod’ ));
>
public function MyCallbackMethod ()
<
echo $this -> property ;
>
Performance note: The callable type hint, like is_callable(), will trigger an autoload of the class if the value looks like a static method callback.
When specifying a call back in array notation (ie. array($this, «myfunc») ) the method can be private if called from inside the class, but if you call it from outside you’ll get a warning:
class mc <
public function go (array $arr ) <
array_walk ( $arr , array( $this , «walkIt» ));
>
private function walkIt ( $val ) <
echo $val . «
» ;
>
public function export () <
return array( $this , ‘walkIt’ );
>
>
$m = new mc ;
$m -> go ( $data ); // valid
array_walk ( $data , $m -> export ()); // will generate warning
?>
Output:
1
2
3
4
Warning: array_walk() expects parameter 2 to be a valid callback, cannot access private method mc::walkIt() in /in/tfh7f on line 22
A note on differences when calling callbacks as «variable functions» without the use of call_user_func() (e.g. » «):
— Using the name of a function as string has worked since at least 4.3.0
— Calling anonymous functions and invokable objects has worked since 5.3.0
— Using the array structure [$object, ‘method’] has worked since 5.4.0
Note, however, that the following are not supported when calling callbacks as variable functions, even though they are supported by call_user_func():
— Calling static class methods via strings such as ‘foo::doStuff’
— Calling parent method using the [$object, ‘parent::method’] array structure
All of these cases are correctly recognized as callbacks by the ‘callable’ type hint, however. Thus, the following code will produce an error «Fatal error: Call to undefined function foo::doStuff() in /tmp/code.php on line 4»:
class foo static function callIt (callable $callback ) $callback ();
>
static function doStuff () echo «Hello World!» ;
>
>
foo :: callIt ( ‘foo::doStuff’ );
?>
The code would work fine, if we replaced the ‘$callback()’ with ‘call_user_func($callback)’ or if we used the array [‘foo’, ‘doStuff’] as the callback instead.
You can use ‘self::methodName’ as a callable, but this is dangerous. Consider this example:
class Foo public static function doAwesomeThings () FunctionCaller :: callIt ( ‘self::someAwesomeMethod’ );
>
public static function someAwesomeMethod () // fantastic code goes here.
>
>
class FunctionCaller public static function callIt (callable $func ) call_user_func ( $func );
>
>
Foo :: doAwesomeThings ();
?>
This results in an error:
Warning: class ‘FunctionCaller’ does not have a method ‘someAwesomeMethod’.
For this reason you should always use the full class name:
FunctionCaller :: callIt ( ‘Foo::someAwesomeMethod’ );
?>
I believe this is because there is no way for FunctionCaller to know that the string ‘self’ at one point referred to to `Foo`.
> As of PHP 5.2.3, it is also possible to pass ‘ClassName::methodName’
You can also use ‘self::methodName’. This works in PHP 5.2.12 for me.
If you pass a callable method to a function with a callable type declaration, the error message is misleading:
class X protected function foo (): void <>
>
$x = new X ;
$c = [ $x , ‘foo’ ];
bar ( $c );
?>
Error message will be something like «Argument #1 ($c) must be of type callable, array given» while the actual problem here is only the visibility of method «foo». All you need to do is changing it to public (or use a different approach, e.g. with a Closure).
I needed a function that would determine the type of callable being passed, and, eventually,
normalized it to some extent. Here’s what I came up with:
/**
* The callable types and normalizations are given in the table below:
*
* Callable | Normalization | Type
* ———————————+———————————+—————
* function (. ) use (. ) <. >| function (. ) use (. ) <. >| ‘closure’
* $object | $object | ‘invocable’
* «function» | «function» | ‘function’
* «class::method» | [«class», «method»] | ‘static’
* [«class», «parent::method»] | [«parent of class», «method»] | ‘static’
* [«class», «self::method»] | [«class», «method»] | ‘static’
* [«class», «method»] | [«class», «method»] | ‘static’
* [$object, «parent::method»] | [$object, «parent::method»] | ‘object’
* [$object, «self::method»] | [$object, «method»] | ‘object’
* [$object, «method»] | [$object, «method»] | ‘object’
* ———————————+———————————+—————
* other callable | idem | ‘unknown’
* ———————————+———————————+—————
* not a callable | null | false
*
* If the «strict» parameter is set to true, additional checks are
* performed, in particular:
* — when a callable string of the form «class::method» or a callable array
* of the form [«class», «method»] is given, the method must be a static one,
* — when a callable array of the form [$object, «method»] is given, the
* method must be a non-static one.
*
*/
function callableType ( $callable , $strict = true , callable& $norm = null ) if (! is_callable ( $callable )) switch ( true ) case is_object ( $callable ):
$norm = $callable ;
return ‘Closure’ === get_class ( $callable ) ? ‘closure’ : ‘invocable’ ;
case is_string ( $callable ):
$m = null ;
if ( preg_match ( ‘~^(?[a-z_][a-z0-9_]*)::(?[a-z_][a-z0-9_]*)$~i’ , $callable , $m )) list( $left , $right ) = [ $m [ ‘class’ ], $m [ ‘method’ ]];
if (! $strict || (new \ ReflectionMethod ( $left , $right ))-> isStatic ()) $norm = [ $left , $right ];
return ‘static’ ;
>
> else $norm = $callable ;
return ‘function’ ;
>
break;
case is_array ( $callable ):
$m = null ;
if ( preg_match ( ‘~^(:?(?self|parent)::)?(?[a-z_][a-z0-9_]*)$~i’ , $callable [ 1 ], $m )) if ( is_string ( $callable [ 0 ])) if ( ‘parent’ === strtolower ( $m [ ‘reference’ ])) list( $left , $right ) = [ get_parent_class ( $callable [ 0 ]), $m [ ‘method’ ]];
> else list( $left , $right ) = [ $callable [ 0 ], $m [ ‘method’ ]];
>
if (! $strict || (new \ ReflectionMethod ( $left , $right ))-> isStatic ()) $norm = [ $left , $right ];
return ‘static’ ;
>
> else if ( ‘self’ === strtolower ( $m [ ‘reference’ ])) list( $left , $right ) = [ $callable [ 0 ], $m [ ‘method’ ]];
> else list( $left , $right ) = $callable ;
>
if (! $strict || !(new \ ReflectionMethod ( $left , $right ))-> isStatic ()) $norm = [ $left , $right ];
return ‘object’ ;
>
>
>
break;
>
$norm = $callable ;
return ‘unknown’ ;
>
$norm = null ;
return false ;
>
?>
Hope someone else finds it useful.
How to Use Callbacks in PHP
A callback is considered a function reference/object with the type callable.
It can act as an object method, a function, or a static class method.
Here, we will demonstrate the ways of using standard callbacks, static class method callbacks, object method callbacks, as well as closure callbacks.
Using Standard Callbacks
In PHP, you can call functions with the help of the call_user_func() function. The argument is the string name of the function that is going to be called.
// PHP program to demonstrate work // of a standard callback // Function for printing a string function someFunction( ) < echo "W3docs \n"; > // Standard callback call_user_func('someFunction'); ?>Using Static Class Method Callback
In PHP, you can call static methods with the help of call_user_func() . Here, the argument is an array that includes the class string name and the method within it to be called.
// PHP program to demonstrate the working // of a Static class method callback // Sample class class GFG < // Function used for printing a string static function someFunction( ) < echo "Parent W3docs \n"; > > class Article extends GFG < // Function for printing a string static function someFunction( ) < echo "W3docs Article \n"; > > // Static class method callback call_user_func(['Article', 'someFunction']); call_user_func('Article::someFunction'); // Relative Static class method callback call_user_func(['Article', 'parent::someFunction']); ?>W3docs Article W3docs Article Parent W3docs
Using Object Method Callback
In PHP, you can call object methods with the help of call_user_func() . Here the argument is an array that includes the object variable and the method string name to be called.
Let’s check out an example:
// PHP program to demonstrate the working // of a object method callback // Sample class class GFG < // Function to print a string static function someFunction( ) < echo "W3docs \n"; > // The __invoke() method is called when a script tries to call an object as a function. public function __invoke( ) < echo "invoke W3docs \n"; > > // Class object $obj = new GFG(); // Object method call call_user_func([$obj, 'someFunction']); // Callable __invoke method object call_user_func($obj); ?>Closure Callbacks
You can make closure functions callable through standard calls or by mapping the closure function to the array of valid arguments sent to the closure with array_map() . Here, the closure function and the array of its valid arguments are considered the arguments of the function.
The example will look as follows:
// PHP program to demonstrate the working // of a closure callback // Closure for printing a string $print_function = function ($string) < echo $string . "\n"; >; // Array of strings $string_array = ["Geeksforgeeks", "GFG", "Article"]; // Callable closure array_map($print_function, $string_array); ?>Geeksforgeeks GFG Article
Using anonymous functions
// Array of strings $string_array = ["Geeksforgeeks", "GFG", "Article"]; // Callable closure array_map(function($string) < echo $string . "\n"; >, $string_array); ?>Geeksforgeeks GFG Article