Hướng dẫn type callable php

Callbacks can be denoted by the callable type declaration.

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.

Passing

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. Accessing protected and private methods from within a class is allowed.

Static class methods can also be passed without instantiating an object of that class by either, passing the class name instead of an object at index 0, or passing 'ClassName::methodName'.

Apart from common user-defined function, anonymous functions and arrow functions can also be passed to a callback parameter.

Note:

As of PHP 8.1.0, anonymous functions can also be created using the first class callable syntax.

Generally, any object implementing __invoke() can also be passed to a callback parameter.

Example #1 Callback function examples

// 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
call_user_func('MyClass::myCallbackMethod');// Type 5: Relative static class method call
class {
    public static function 
who() {
        echo 
"A\n";
    }
}

class

extends {
    public static function 
who() {
        echo 
"B\n";
    }
}
call_user_func(array('B''parent::who')); // A

// Type 6: Objects implementing __invoke can be used as callables

class {
    public function 
__invoke($name) {
        echo 
'Hello '$name"\n";
    }
}
$c = new C();
call_user_func($c'PHP!');
?>

Example #2 Callback example using a Closure

// Our closure
$double = function($a) {
    return 
$a 2;
};
// This is our range of numbers
$numbers range(15);// Use the closure as a callback here to
// double the size of each element in our
// range
$new_numbers array_map($double$numbers);

print

implode(' '$new_numbers);
?>

The above example will output:

Note:

Callbacks registered with functions such as call_user_func() and call_user_func_array() will not be called if there is an uncaught exception thrown in a previous callback.

andrewbessa at gmail dot com

10 years ago

You can also use the $this variable to specify a callback:

class MyClass {

    public

$property = 'Hello World!';

    public function

MyMethod()
    {
       
call_user_func(array($this, 'myCallbackMethod'));
    }

    public function

MyCallbackMethod()
    {
        echo
$this->property;
    }

}

?>

steve at mrclay dot org

10 years ago

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.

computrius at gmail dot com

8 years ago

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');
    }
}
$data = array(1,2,3,4); $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

Riikka K

7 years ago

A note on differences when calling callbacks as "variable functions" without the use of call_user_func() (e.g. "= 'printf'; $callback('Hello World!') ?>"):

- 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.

edanschwartz at gmail dot com

7 years ago

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`.

InvisibleSmiley

1 year ago

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 {}
}

function

bar(callable $c) {}$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).

Yzmir Ramirez

8 years ago

> 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.

mariano dot REMOVE dot perez dot rodriguez at gmail dot com

7 years ago

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.

bradyn at NOSPAM dot bradynpoulsen dot com

6 years ago

When trying to make a callable from a function name located in a namespace, you MUST give the fully qualified function name (regardless of the current namespace or use statements).

namespace MyNamespace;

function

doSomethingFancy($arg1)
{
   
// do something...
}$values = [1, 2, 3];array_map('doSomethingFancy', $values);
// array_map() expects parameter 1 to be a valid callback, function 'doSomethingFancy' not found or invalid function namearray_map('MyNamespace\doSomethingFancy', $values);
// => [..., ..., ...]

gulaschsuppe2 at gmail dot com

3 years ago

I tried many possible ways of calling functions by function name directly and assigned to a variable on 3v4l. Not mentioned yet, it is possible to use an array as a caller, at least since PHP 7.1.25. The following script contains all the information I gained:

// Call function via function name:
    // Basics:
        // A function can also be called by using its string name:
       
function callbackFunc() {
            echo
'Hello World';
        }
'callbackFunc'(); // Hello World

                                    // A function can also be called if its name is assigned to a variable:

function callbackFunc() {
                echo
'Hello World';
            }
$funcName = 'callbackFunc';
           
$funcName(); // Hello World

    // Static class method:
        // It is also possible to call a public static class method via 'ClassName::functioName' notation:

class A {
                public static function
callbackMethod() {
                    echo
"Hello World\n";
                }
            }
           
'A::callbackMethod'(); // Hello World$funcName = 'A::callbackMethod';
           
$funcName(); // Hello World

    // Non static class method:
        // It is also possible to call non static class methods by creating an array which first element is the object the method should be called on and the second element is the non static method to be called. The array can directly be used as a caller:

class A {
                private
$prop = "Hello World\n";

                public function

callbackMethod() {
                    echo
$this->prop;
                }
            }
$a = new A;
            [
$a, 'callbackMethod']();
           
$funcCallArr = [$a, 'callbackMethod'];
           
$funcCallArr();// Of course this also works inside the class with '$this':
           
class A {
                private function
privCallback() {
                    echo
'Private';
                }

                public function

privCallbackCaller($funcName) {
                    [
$this, $funcName]();
                }
            }

            (new

A)->privCallbackCaller('privCallback'); // Private?>

Daniel Klein

5 years ago

You can use "self::method_name", "static::method_name" and "parent::method_name" in callables:

class StaticCallable {
    public static function
foo($values) {
        return
array_map('self::bar', $values);
    }

    public static function

bar($value) {
        return
"{$value}: 42";
    }

    public static function

baz($values) {
        return
array_map('static::qux', $values);
    }

    public static function

qux($value) {
        return
"{$value}: 123";
    }
}

class

StaticExtension extends StaticCallable {
    public static function
bar($value) {
        return
"{$value}: Marvin the Paranoid Android";
    }

    public static function

qux($value) {
        return
"{$value}: Zaphod Beeblebrox";
    }
}
print_r(StaticCallable::foo([1, 2, 3]));
print_r(StaticExtension::foo([1, 2, 3]));print_r(StaticCallable::baz([1, 2, 3]));
print_r(StaticExtension::baz([1, 2, 3]));
?>

Results:
Array
(
    [0] => 1: 42
    [1] => 2: 42
    [2] => 3: 42
)
Array
(
    [0] => 1: 42
    [1] => 2: 42
    [2] => 3: 42
)
Array
(
    [0] => 1: 123
    [1] => 2: 123
    [2] => 3: 123
)
Array
(
    [0] => 1: Zaphod Beeblebrox
    [1] => 2: Zaphod Beeblebrox
    [2] => 3: Zaphod Beeblebrox
)

"self::" uses the same class as the called method, "static::" uses the same class as the called class, and "parent::" (not shown) uses the parent class, or generates a warning if there is no parent.

pawel dot tadeusz dot niedzielski at gmail dot com

6 years ago

@edanschwartz at gmail dot com

You can use ::class property to always indicate the class you're in when using static methods:

class Foo {
    public static function
doAwesomeThings() {
       
FunctionCaller::callIt(self::class . '::someAwesomeMethod');
    }

    public static function

someAwesomeMethod() {
       
// fantastic code goes here.
   
}
}

class

FunctionCaller {
    public static function
callIt(callable $func) {
       
call_user_func($func);
    }
}
Foo::doAwesomeThings();
?>

whysteepy at gmail dot com

5 years ago

Another Appearance of Callbacks! Here is one way of them - methods of an instantiated object can be callable and implemented as variable functions without php's default functions that can call user-defined callback functions.

class Test {
    protected $items = array();

    public function __construct()
    {
        $this->items[] = array($this, 'callBackOne');
        $this->items[] = array($this, 'callBackTwo');
    }

    public function callBackOne()
    {
        echo __METHOD__ . ' has been called as a callback.';
    }

    public function callBackTwo()
    {
        echo __METHOD__ . ' has been called as a callback.';
    }

    public function getItems()
    {
        return $this->items;
    }
}

$o = new Test();
$itemLists = $o->getItems();

foreach ($itemLists as $itemList) {

        // call each one as a variable function
        echo '

';
        print_r($itemList());
        echo '
';
}

// Outputs the following
// Test::callBackOne has been called as a callback.

// Test::callBackTwo has been called as a callback.

chechomancr at hotmail dot com

7 months ago

In PHP >= 8.0 callIt function with optional parameters.
declare(strict_types = 1);

class

Example {

    public static function

someFunction(string $value, string $a_parameter, int $another_parameter): string
   
{
        
//TODO: Apply the required filter
       
return "$value $a_parameter $another_parameter";
    }

    public static function

callIt(string $callback, ...$parameters): callable
    {
        return static
fn(mixed $value = null) => self::$callback($value, ...$parameters);
    }

}

?>

How to use:
declare(strict_types = 1);$args = [
   
'information' => ['filter'  => FILTER_CALLBACK'options' => Example::callIt('someFunction', 'world', 2022)],
];
$unfiltered_data = ['information' => 'Hello'];$filtered_data = filter_var_array($unfiltered_data, $args);

if(

false === $filtered_data) {
    echo
"Error...", PHP_EOL;
}

echo

var_export($filtered_data, true);
?>

Result: array ( 'information' => 'Hello world 2022' )

chris dot rutledge at gmail dot com

3 years ago

Having read this line in the manual above,

"A method of an instantiated object is passed as an array containing an object at index 0 and the method name at index 1. Accessing protected and private methods from within a class is allowed."

I decided to do some testing to see if I could access private methods using the call_user_func methods. Thankfully not, but for completeness here is my test which also covers using static and object contexts

class foo {

        public static

$isInstance = false;

        public function

__construct() {
       
self::$isInstance = true;
    }

    public function

bar() {
       
var_dump(self::$isInstance);
        echo
__METHOD__;
    }

        private function

baz() {
       
var_dump(self::$isInstance);
        echo
__METHOD__;
    }

        public function

qux() {
       
$this->baz();
    }

        public function

quux() {
       
self::baz();
    }
}
call_user_func(['foo','bar']);    //fase, foo:barcall_user_func(['foo','baz']);  //warning, cannot access private methodcall_user_func(['foo','quux']); //false, foo::bazcall_user_func(['foo','qux']);  //fatal, Using $this when not in object context $foo = new foo;call_user_func([$foo,'bar']);    //true, foo::bar
call_user_func([$foo,'baz']);    //warning, cannot access private method
call_user_func([$foo,'qux']);    //true, foo::bazcall_user_func(['foo','bar']);  //true, foo::bar (static call, yet $isInstance is true)?>

Dan J

4 years ago

You can avoid repeating a long namespace for classes in callable arrays by making use of the "use" operator and the special "::class" constant.

Documentation of use operator:
http://php.net/manual/en/language.namespaces.importing.php

Documentation of ::class constant:
http://php.net/manual/en/language.oop5.constants.php

// Library file with namespace My\Library\Namespace
require 'MyLibrary.php';// Alias for SortingClass
use \My\Library\Namespace\SortingClass;// Callable array referring to SortingClass::SortFunction
$callable = [SortingClass::class, 'SortFunction'];$values = [3, 1, 2];
usort($values, $callable);