Diese Seite bei php.net
The PHP manual text and comments are covered by the Creative Commons Attribution 3.0 License © the PHP Documentation Group - Impressum - mail("TO:Reinhard Neidl",...)
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.
Beispiel #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:
Beispiel #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 declared in the function header. 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:
Beispiel #3 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
?>
Anonymous functions are currently implemented using the Closure class. This is an implementation detail and should not be relied upon.
Hinweis: Anonymous functions are available since PHP 5.3.0.
Hinweis: It is possible to use func_num_args(), func_get_arg(), and func_get_args() from within a closure.
use() parameters are early binding - they use the variable's value at the point where the lambda function is declared, rather than the point where the lambda function is called (late binding).
If you want late binding put & before the variable inside use()
<?php
$fn = function () use (&$var) { echo $var; };
?>
Examples:
<?php
// problem 1: this should echo "Canada", not a php notice
$fn = function () use ($country) { echo $country . "\n"; };
$country = 'Canada';
$fn();
// problem 2: this should echo "Canada", not "UnitedStates"
$country = 'UnitedStates';
$fn = function () use ($country) { echo $country . "\n"; };
$country = 'Canada';
$fn();
// problem 3: this should echo "Canada", not "UnitedStates"
$country = (object)array('name' => 'UnitedStates');
$fn = function () use ($country) { echo $country->name . "\n"; };
$country = (object)array('name' => 'Canada');
$fn();
// problem 4: this outputs "Canada". if this outputs "Canada",
// then so should problem 2 above. otherwise this should be
// just as broken as problem 2 and be outputting "UnitedStates"
$country = (object)array('name' => 'UnitedStates');
$fn = function () use ($country) { echo $country->name . "\n"; };
$country->name = 'Canada';
$fn();
?>
see http://bugs.php.net/bug.php?id=50980
(I've just quoted from there, but if you want you can read there the whole feature request)
As an alternative to gabriel's recursive construction, you may instead assign the recursive function to a variable, and use it by reference, thus:
<?php
$fib = function($n)use(&$fib)
{
if($n == 0 || $n == 1) return 1;
return $fib($n - 1) + $fib($n - 2);
};
echo $fib(10);
?>
Hardly a sensible implementation of the Fibonacci sequence, but that's not the point! The point is that the variable needs to be used by reference, not value.
Without the '&', the anonymous function gets the value of $fib at the time the function is being created. But until the function has been created, $fib can't have it as a value! It's not until AFTER the function has been assigned to $fib that $fib can be used to call the function - but by then it's too late to pass its value to the function being created!
Using a reference resolves the dilemma: when called, the anonymous function will use $fib's current value, which will be the anonymous function itself.
At least, it will be if you don't reassign $fib to anything else between creating the function and calling it:
<?php
$fib = function($n)use(&$fib)
{
if($n == 0 || $n == 1) return 1;
return $fib($n - 1) + $fib($n - 2);
};
$lie = $fib;
$fib = function($n)
{
return 100;
};
echo $lie(10); // 200, because $fib(10 - 1) and $fib(10 - 2) both return 100.
?>
Of course, that's true of any variable: if you don't want its value to change, don't change its value.
All the usual scoping rules for variables still apply: a local variable in a function is a different variable from another one with the same name in another function:
<?php
$fib = function($n)use(&$fib)
{
if($n == 0 || $n == 1) return 1;
return $fib($n - 1) + $fib($n - 2);
};
$bark = function($f)
{
$fib = 'cake'; // A totally different variable from the $fib above.
return 2 * $f(5);
};
echo $bark($fib); // 16, twice the fifth Fibonacci number
?>
Base dao class illustrating the usefulness of closures.
* Handles opening and closing of connections.
* Adds slashes sql
* Type checking of sql parameters and casts as appropriate
* Provides hook for processing of result set and emitting one or more objects.
* Provides hook for accessing underlying link and result objects.
<?php
define("userName","root");
define("password","root");
define("dbName","ahcdb");
define("hostName","localhost");
class BaseDao {
function getConnection() {
$link = mysql_connect(hostName, userName, password);
if (!$link)
die("Could not connect: " . mysql_error());
if (!mysql_select_db(dbName))
die("Could not select database: " . mysql_error());
return $link;
}
function setParams(& $sql, $params) {
if($params != null)
$sql = vsprintf($sql, array_map(function($n) {
if(is_int($n))
return (int)$n;
if(is_float($n))
return (float)$n;
if(is_string($n))
return "'".mysql_real_escape_string($n)."'";
return mysql_real_escape_string($n);
}, $params));
}
function executeQuery($sql, $params, $callback = null) {
$link = $this->getConnection();
$this->setParams($sql, $params);
$return = null;
if(($result = mysql_query($sql, $link)) != null)
if($callback != null)
$return = $callback($result, $link);
if($link != null)
mysql_close($link);
if(!$result)
die("Fatal Error: Invalid query '$sql' : " . mysql_error());
return $return;
}
function getList($sql, $params, $callback) {
return $this->executeQuery($sql, $params, function($result, $link) use ($callback) {
$idx = 0;
$list = array();
while ($row = mysql_fetch_assoc($result))
if($callback != null)
$list[$idx] = $callback($idx++, $row);
return $list;
});
}
function getSingle($sql, $params, $callback) {
return $this->executeQuery($sql, $params, function($result, $link) use ($callback) {
if ($row = mysql_fetch_assoc($result))
$obj = $callback($row);
return $obj;
});
}
}
class Example {
var $id;
var $name;
function Example($id, $name){
$this->id = $id;
$this->name = $name;
}
function setId($id){
$this->id = $id;
}
}
class ExampleDao extends BaseDao {
function getAll(){
return parent::getList("select * from nodes", null, function($idx, $row) {
return new Example($row["id"], $row["name"]);
});
}
function load($id){
return parent::getSingle("select * from nodes where id = %1\$s", array($id), function($row) {
return new Example($row["id"], $row["name"]);
});
}
function update($example){
return parent::executeQuery("update nodes set name = '' where id = -1", null, function($result, $link){
return $result;
});
}
function insert(& $example){
return parent::executeQuery("insert into nodes", null, function($result, $link) use ($example){
$id = mysql_insert_id($link);
$example->setId($id);
return $result;
});
}
}
$exampleDao = new ExampleDao();
$list = $exampleDao->getAll());
$exampleObject = $exampleDao->load(1));
$exampleDao->update($exampleObject);
?>
Watch out when 'importing' variables to a closure's scope -- it's easy to miss / forget that they are actually being *copied* into the closure's scope, rather than just being made available.
So you will need to explicitly pass them in by reference if your closure cares about their contents over time:
<?php
$result = 0;
$one = function()
{ var_dump($result); };
$two = function() use ($result)
{ var_dump($result); };
$three = function() use (&$result)
{ var_dump($result); };
$result++;
$one(); // outputs NULL: $result is not in scope
$two(); // outputs int(0): $result was copied
$three(); // outputs int(1)
?>
Another less trivial example with objects (what I actually tripped up on):
<?php
//set up variable in advance
$myInstance = null;
$broken = function() uses ($myInstance)
{
if(!empty($myInstance)) $myInstance->doSomething();
};
$working = function() uses (&$myInstance)
{
if(!empty($myInstance)) $myInstance->doSomething();
}
//$myInstance might be instantiated, might not be
if(SomeBusinessLogic::worked() == true)
{
$myInstance = new myClass();
}
$broken(); // will never do anything: $myInstance will ALWAYS be null inside this closure.
$working(); // will call doSomething if $myInstance is instantiated
?>
If you want to make a recursive closure, you will need to write this:
$some_var1="1";
$some_var2="2";
function($param1, $param2) use ($some_var1, $some_var2)
{
//some code here
call_user_func(__FUNCTION__, $other_param1, $other_param2);
//some code here
}
If you need to pass values by reference you should check out
http://www.php.net/manual/en/function.call-user-func.php
http://www.php.net/manual/en/function.call-user-func-array.php
If you're wondering if $some_var1 and $some_var2 are still visible by using the call_user_func, yes, they are available.
$this is currently (PHP 5.3.2) not usable directly with closures.
One can write:
<?php
$self = $this;
function () use ($self) { ... }
?>
but then the private/protected members of $this cannot be used inside the closure. This makes closures much less useful in OO code.
Until this is fixed, one can cheat using reflection:
<?php
class FullAccessWrapper
{
protected $_self;
protected $_refl;
public function __construct($self)
{
$this->_self = $self;
$this->_refl = new ReflectionObject($self);
}
public function __call($method, $args)
{
$mrefl = $this->_refl->getMethod($method);
$mrefl->setAccessible(true);
return $mrefl->invokeArgs($this->_self, $args);
}
public function __set($name, $value)
{
$prefl = $this->_refl->getProperty($name);
$prefl->setAccessible(true);
$prefl->setValue($this->_self, $value);
}
public function __get($name)
{
$prefl = $this->_refl->getProperty($name);
$prefl->setAccessible(true);
return $prefl->getValue($this->_self);
}
public function __isset($name)
{
$value = $this->__get($name);
return isset($value);
}
}
/**
* Usage:
* $self = giveAccess($this);
* function() use ($self) { $self->privateMember... }
*/
function giveAccess($obj)
{
return new FullAccessWrapper($obj);
}
// Example:
class Foo
{
private $x = 3;
private function f()
{
return 15;
}
public function getClosureUsingPrivates()
{
$self = giveAccess($this);
return function () use ($self) {
return $self->x * $self->f();
};
}
}
$foo = new Foo();
$closure = $foo->getClosureUsingPrivates();
echo $closure() . "\n"; // Prints 45 as expected
?>
Here is an example of one way to define, then use the variable ( $this ) in Closure functions. The code below explores all uses, and shows restrictions.
The most useful tool in this snippet is the requesting_class() function that will tell you which class is responsible for executing the current Closure().
Overview:
-----------------------
Successfully find calling object reference.
Successfully call $this(__invoke);
Successfully reference $$this->name;
Successfully call call_user_func(array($this, 'method'))
Failure: reference anything through $this->
Failure: $this->name = '';
Failure: $this->delfect();
<?php
function requesting_class()
{
foreach(debug_backtrace(true) as $stack){
if(isset($stack['object'])){
return $stack['object'];
}
}
}
class Person
{
public $name = '';
public $head = true;
public $feet = true;
public $deflected = false;
function __invoke($p){ return $this->$p; }
function __toString(){ return 'this'; } // test for reference
function __construct($name){ $this->name = $name; }
function deflect(){ $this->deflected = true; }
public function shoot()
{ // If customAttack is defined, use that as the shoot resut. Otherwise shoot feet
if(is_callable($this->customAttack)){
return call_user_func($this->customAttack);
}
$this->feet = false;
}
}
$p = new Person('Bob');
$p->customAttack =
function(){
echo $this; // Notice: Undefined variable: this
#$this = new Class() // FATAL ERROR
// Trick to assign the variable '$this'
extract(array('this' => requesting_class())); // Determine what class is responsible for making the call to Closure
var_dump( $this ); // Passive reference works
var_dump( $$this ); // Added to class: function __toString(){ return 'this'; }
$name = $this('name'); // Success
echo $name; // Outputs: Bob
echo '<br />';
echo $$this->name;
call_user_func_array(array($this, 'deflect'), array()); // SUCCESSFULLY CALLED
#$this->head = 0; //** FATAL ERROR: Using $this when not in object context
$$this->head = 0; // Successfully sets value
};
print_r($p);
$p->shoot();
print_r($p);
die();
?>
In the code
<?php
function new_counter()
{
$counter = mt_rand();
return function()use(&$counter)
{
return ++$counter;
};
}
$t1 = new_counter();
$t2 = new_counter();
echo $t1(),"\n";
echo $t1(),"\n";
echo $t2(),"\n";
echo $t2(),"\n";
echo $t1(),"\n";
echo $t1(),"\n";
?>
The variable $counter is local to new_counter() and is used by reference by the returned lambda function.
Because $counter is not static, a new variable is created each time new_counter() is called.
But because the lambda function uses a REFERENCE to the $counter variable - and not a new local variable with a copy of the value $counter had when the lambda function was constructed - the $counter variable created when new_counter() ran still exists (because a reference to it still exists).
Every lambda function has a variable reference "hardwired" into it. That variable therefore persists across calls to the lambda function - rather like a static variable.
But that variable is only LOCAL to the new_counter() function that created it. As soon as new_counter() returns, it gives up its reference to $counter. When new_counter() is called again, it gets allocated a NEW $counter variable and gives a reference to THAT variable to the lambda function it constructs.
So the lambda functions in $t1 and $t2 each have their OWN $counter variable - separate from the other's, which persists from one call to the next.
The effect is very similar to declaring and initialising $counter as static within the lambda function - and then it doesn't need to use anything from new_counter() - but you can't initialise a static variable with a function call like mt_rand()!
Pending a decision on what it should mean, $this is not currently (as of 5.3.2) usable within anonymous functions.
There are roughly two positions (plus attempts at compromise), that can be called "early" and "late".
Early: $this refers to the object in whose scope the anonymous function is constructed.
<?php
class Creator
{
public function make_anonymous()
{
return function()
{
return $this;
};
}
}
class Caller
{
public $p;
public function call_anonymous($f)
{
$this->p = $f();
}
}
$alpha = new Creator;
$omega = new Caller;
$omega->call_anonymous($alpha->create_anonymous());
// $omega->p === $alpha
?>
Late: $this refers to the object in whose scope the anonymous function is called.
<?php
class Creator
{
public function make_anonymous()
{
return function()
{
return $this;
};
}
}
class Caller
{
public $p;
public function call_anonymous($f)
{
$this->p = $f();
}
}
$alpha = new Creator;
$omega = new Caller;
$omega->call_anonymous($alpha->create_anonymous());
// $omega->p === $omega
?>
So until this is cleared up, $this won't work in an anonymous function. (Personally, I favour the early method; otherwise the anonymous function - and therefore its Creator - has access to all of the Caller's private properties.)
If you want to make sure that one of the parameters of your function is a Closure, you can use Type Hinting.
see: http://php.net/manual/en/language.oop5.typehinting.php
Example:
<?php
class TheRoot
{
public function poidh($param) {
echo "TheRoot $param!";
}
}
class Internet
{
# here, $my_closure must be of type object Closure
public function run_my_closure($bar, Closure $my_closure) {
$my_closure($bar);
}
}
$Internet = new Internet();
$Root = new TheRoot();
$Internet->run_my_closure($Root, function($Object) {
$Object->poidh(42);
});
?>
The above code simply yields:
"TheRoot 42!"
NOTE: If you are using namespaces, make sure you give a fully qualified namespace.
print_r() of Internet::run_my_closure's $my_closure
<?php
Closure Object
(
[parameter] => Array
(
[$Object] =>
)
)
?>
var_dump() of Internet::run_my_closure's $my_closure
<?php
object(Closure)#3 (1) {
["parameter"]=>
array(1) {
["$Object"]=>
string(10) ""
}
}
?>
Anonymous functions are great for events!
<?php
class Event {
public static $events = array();
public static function bind($event, $callback, $obj = null) {
if (!self::$events[$event]) {
self::$events[$event] = array();
}
self::$events[$event][] = ($obj === null) ? $callback : array($obj, $callback);
}
public static function run($event) {
if (!self::$events[$event]) return;
foreach (self::$events[$event] as $callback) {
if (call_user_func($callback) === false) break;
}
}
}
function hello() {
echo "Hello from function hello()\n";
}
class Foo {
function hello() {
echo "Hello from foo->hello()\n";
}
}
class Bar {
function hello() {
echo "Hello from Bar::hello()\n";
}
}
$foo = new Foo();
// bind a global function to the 'test' event
Event::bind("test", "hello");
// bind an anonymous function
Event::bind("test", function() { echo "Hello from anonymous function\n"; });
// bind an class function on an instance
Event::bind("test", "hello", $foo);
// bind a static class function
Event::bind("test", "Bar::hello");
Event::run("test");
/* Output
Hello from function hello()
Hello from anonymous function
Hello from foo->hello()
Hello from Bar::hello()
*/
?>
appears kwilson at shuttlebox dot net that you may have just made unintended side effect. Note that adding the global $variable to your test function make the closure function echo second rather than first So the anonymous function works as expected with respect to globals.
<?php
$variable = "first";
$closure = function() {
global $variable;
echo $variable . "\n";
};
$closure();
function test($closure)
{
global $variable; //Note the scope added here
$variable = "second";
$closure();
}
test($closure);
?>
prints:
first
second
tested with php 5.3.1
Using the global keyword apparently pulls variables from the scope where the function was created, not where it is executed.
Example:
<?php
$variable = "first";
$closure = function() {
global $variable;
echo $variable . "\n";
};
$closure();
function test($closure)
{
$variable = "second";
$closure();
}
test($closure);
?>
Will print:
first
first
hello there!
here is a little code which shows use of the closures as event handlers:
<?php
class Button
{
public $OnBeforeClick;
public $OnAfterClick;
public $Name;
function Button()
{
$this->Name = 'MyButton';
}
public function Click()
{
$this->DoBeforeClick();
echo 'Click!';
$this->DoAfterClick();
}
private function DoBeforeClick()
{
if (isset($this->OnBeforeClick))
{
$Event = $this->OnBeforeClick;
$Event($this);
}
}
private function DoAfterClick()
{
if (isset($this->OnAfterClick))
{
$Event = $this->OnAfterClick;
$Event($this);
}
}
}
//eclipse may warn here about syntax error but no problem, it runs well.
$BeforeClickEventHandler = function($Sender) { echo $Sender->Name . ' (Before Click)'; };
$AfterClickEventHandler = function($Sender) { echo $Sender->Name . ' (After Click)'; };
$MyWidget = new Button();
$MyWidget->OnBeforeClick = $BeforeClickEventHandler;
$MyWidget->OnAfterClick = $AfterClickEventHandler;
$MyWidget->Click();
?>
output:
MyButton (Before Click)
Click!
MyButton (After Click)
i hope you find this useful.
regards.
emre
You can always call protected members using the __call() method - similar to how you hack around this in Ruby using send.
<?php
class Fun
{
protected function debug($message)
{
echo "DEBUG: $message\n";
}
public function yield_something($callback)
{
return $callback("Soemthing!!");
}
public function having_fun()
{
$self =& $this;
return $this->yield_something(function($data) use (&$self)
{
$self->debug("Doing stuff to the data");
// do something with $data
$self->debug("Finished doing stuff with the data.");
});
}
// Ah-Ha!
public function __call($method, $args = array())
{
if(is_callable(array($this, $method)))
return call_user_func_array(array($this, $method), $args);
}
}
$fun = new Fun();
echo $fun->having_fun();
?>
To recursively call a closure, use this code.
<?php
$recursive = function () use (&$recursive){
// The function is now available as $recursive
}
?>
This DOES NOT WORK
<?php
$recursive = function () use ($recursive){
// The function is now available as $recursive
}
?>
be aware of Fatal error: Using $this when not in object context when using in closures
http://wiki.php.net/rfc/closures/removal-of-this
The text above the third example tries to explain that anonymous functions can inherit variables from the parent scope, but fails to properly explain how this is done: namely using the "use" keyword in the function definition.
The following page has a much more detailed explanation of closures in PHP 5.3:
http://wiki.php.net/rfc/closures
Ulderico had it almost right. To avoid confusing the interpreter, when using a simple closure stored in a $variable, you must invoke the nameless function using the function syntax.
<?php
$helloworld = function(){
return "each hello world is different... ".date("His");
};
echo $helloworld( );
?>
Note the empty actual-parameter list in the "echo". NOW IT WORKS.
If you want to check whether you're dealing with a closure specifically and not a string or array callback you can do this:
<?php
$isAClosure = is_callable($thing) && is_object($thing);
?>
Unfortunately, you can't get a pointer to a function, the only function pointers are ones which use anonymous functions as they're created.
This wont work:
<?php
$info = phpinfo;
$info();
//or
function foo() {
echo 'bar';
}
$foo = foo;
$foo();
?>
Because of the behavior of $foo(), it will assume $foo is a string, and try to run the function with the name stored in the string.
Example using uasort.
<?php
// Usual method.
function cmp($a, $b) {
return($a > $b);
}
uasort($array, 'cmp');
// New
uasort($array, function($a, $b) {
return($a > $b);
});
?>
When using anonymous functions as properties in Classes, note that there are three name scopes: one for constants, one for properties and one for methods. That means, you can use the same name for a constant, for a property and for a method at a time.
Since a property can be also an anonymous function as of PHP 5.3.0, an oddity arises when they share the same name, not meaning that there would be any conflict.
Consider the following example:
<?php
class MyClass {
const member = 1;
public $member;
public function member () {
return "method 'member'";
}
public function __construct () {
$this->member = function () {
return "anonymous function 'member'";
};
}
}
header("Content-Type: text/plain");
$myObj = new MyClass();
var_dump(MyClass::member); // int(1)
var_dump($myObj->member); // object(Closure)#2 (0) {}
var_dump($myObj->member()); // string(15) "method 'member'"
$myMember = $myObj->member;
var_dump($myMember()); // string(27) "anonymous function 'member'"
?>
That means, regular method invocations work like expected and like before. The anonymous function instead, must be retrieved into a variable first (just like a property) and can only then be invoked.
Best regards,
Diese Seite bei php.net