No cache version.
Caching disabled. Default setting for this page:enabled (code LNG204)If the display is too slow, you can disable the user mode to view the cached version.
Anonymous functions
Anonymous functions, also known as closures, allow the creation of functions which have no specified name. They are most useful as the value of callback parameters, but they have many other uses.
Anonymous functions are implemented using the Closure class.
Example #1 Anonymous function example
<?php
echo preg_replace_callback('~-([a-z])~', function ($match) {
return strtoupper($match[1]);
}, 'hello-world');
// outputs helloWorld
?>
Closures can also be used as the values of variables; PHP automatically converts such expressions into instances of the Closure internal class. Assigning a closure to a variable uses the same syntax as any other assignment, including the trailing semicolon:
Example #2 Anonymous function variable assignment example
<?php
$greet = function($name)
{
printf("Hello %s\r\n", $name);
};
$greet('World');
$greet('PHP');
?>
Closures may also inherit variables from the parent scope. Any such variables must be passed to the use language construct. From PHP 7.1, these variables must not include superglobals, $this, or variables with the same name as a parameter.
Example #3 Inheriting variables from the parent scope
<?php
$message = 'hello';
// No "use"
$example = function () {
var_dump($message);
};
$example();
// Inherit $message
$example = function () use ($message) {
var_dump($message);
};
$example();
// Inherited variable's value is from when the function
// is defined, not when called
$message = 'world';
$example();
// Reset message
$message = 'hello';
// Inherit by-reference
$example = function () use (&$message) {
var_dump($message);
};
$example();
// The changed value in the parent scope
// is reflected inside the function call
$message = 'world';
$example();
// Closures can also accept regular arguments
$example = function ($arg) use ($message) {
var_dump($arg . ' ' . $message);
};
$example("hello");
?>
The above example will output something similar to:
Notice: Undefined variable: message in /example.php on line 6 NULL string(5) "hello" string(5) "hello" string(5) "hello" string(5) "world" string(11) "hello world"
Inheriting variables from the parent scope is not the same as using global variables. Global variables exist in the global scope, which is the same no matter what function is executing. The parent scope of a closure is the function in which the closure was declared (not necessarily the function it was called from). See the following example:
Example #4 Closures and scoping
<?php
// A basic shopping cart which contains a list of added products
// and the quantity of each product. Includes a method which
// calculates the total price of the items in the cart using a
// closure as a callback.
class Cart
{
const PRICE_BUTTER = 1.00;
const PRICE_MILK = 3.00;
const PRICE_EGGS = 6.95;
protected $products = array();
public function add($product, $quantity)
{
$this->products[$product] = $quantity;
}
public function getQuantity($product)
{
return isset($this->products[$product]) ? $this->products[$product] :
FALSE;
}
public function getTotal($tax)
{
$total = 0.00;
$callback =
function ($quantity, $product) use ($tax, &$total)
{
$pricePerItem = constant(__CLASS__ . "::PRICE_" .
strtoupper($product));
$total += ($pricePerItem * $quantity) * ($tax + 1.0);
};
array_walk($this->products, $callback);
return round($total, 2);
}
}
$my_cart = new Cart;
// Add some items to the cart
$my_cart->add('butter', 1);
$my_cart->add('milk', 3);
$my_cart->add('eggs', 6);
// Print the total with a 5% sales tax.
print $my_cart->getTotal(0.05) . "\n";
// The result is 54.29
?>
Example #5 Automatic binding of $this
<?php
class Test
{
public function testing()
{
return function() {
var_dump($this);
};
}
}
$object = new Test;
$function = $object->testing();
$function();
?>
The above example will output:
object(Test)#1 (0) {
}
Output of the above example in PHP 5.3:
Notice: Undefined variable: this in script.php on line 8 NULL
As of PHP 5.4.0, when declared in the context of a class, the current class is automatically bound to it, making $this available inside of the function's scope. If this automatic binding of the current class is not wanted, then static anonymous functions may be used instead.
Static anonymous functions
As of PHP 5.4, anonymous functions may be declared statically. This prevents them from having the current class automatically bound to them. Objects may also not be bound to them at runtime.
Example #6 Attempting to use $this inside a static anonymous function
<?php
class Foo
{
function __construct()
{
$func = static function() {
var_dump($this);
};
$func();
}
};
new Foo();
?>
The above example will output:
Notice: Undefined variable: this in %s on line %d NULL
Example #7 Attempting to bind an object to a static anonymous function
<?php
$func = static function() {
// function body
};
$func = $func->bindTo(new StdClass);
$func();
?>
The above example will output:
Warning: Cannot bind an instance to a static closure in %s on line %d
Changelog
| Version | Description |
|---|---|
| 7.1.0 | Anonymous functions may not close over superglobals, $this, or any variable with the same name as a parameter. |
| 5.4.0 | Anonymous functions may use $this, as well as be declared statically. |
| 5.3.0 | Anonymous functions become available. |
Notes
Note: It is possible to use func_num_args(), func_get_arg(), and func_get_args() from within a closure.
English translation
You have asked to visit this site in English. For now, only the interface is translated, but not all the content yet.If you want to help me in translations, your contribution is welcome. All you need to do is register on the site, and send me a message asking me to add you to the group of translators, which will give you the opportunity to translate the pages you want. A link at the bottom of each translated page indicates that you are the translator, and has a link to your profile.
Thank you in advance.
Document created the 30/01/2003, last modified the 26/10/2018
Source of the printed document:https://www.gaudry.be/en/php-rf-functions.anonymous.html
The infobrol is a personal site whose content is my sole responsibility. The text is available under CreativeCommons license (BY-NC-SA). More info on the terms of use and the author.
References
These references and links indicate documents consulted during the writing of this page, or which may provide additional information, but the authors of these sources can not be held responsible for the content of this page.
The author This site is solely responsible for the way in which the various concepts, and the freedoms that are taken with the reference works, are presented here. Remember that you must cross multiple source information to reduce the risk of errors.
