PHP 7.4.25 Released!

Funções anônimas

Funções anônimas, também conhecidas como closures, permitem a criação de funções que não tem o nome especificado. Elas são mais úteis como o valor de parâmetros callback, mas podem ter vários outros usos.

Funções anônimas são implementadas utilizando a classe Closure

Exemplo #1 Exemplo de função anônima

<?php
echo preg_replace_callback('~-([a-z])~', function ($match) {
    return 
strtoupper($match[1]);
}, 
'hello-world');
// outputs helloWorld
?>

Closures também podem ser utilizadas como valores de variáveis; o PHP automaticamente converte expressões assim em instâncias da classe interna Closure. Definindo um closure a uma variável usa a mesma sintaxe que qualquer outra definição, incluindo o ponto-e-vírgula:

Exemplo #2 Exemplo de como definir uma função anônima para uma variável

<?php
$greet 
= function($name)
{
    
printf("Hello %s\r\n"$name);
};

$greet('World');
$greet('PHP');
?>

Closures também podem herdar variáveis do escopo pai. Essas variáveis precisam ser referenciadas utilizando a instrução use. A partir do PHP 7.1, essas variáveis não devem incluir superglobals, $this, ou variáveis com o mesmo nome como um parâmetro.

Exemplo #3 Herdando variáveis do escopo anterior

<?php
$message 
'hello';

// Sem "use"
$example = function () {
    
var_dump($message);
};
$example();

// Inherit $message
$example = function () use ($message) {
    
var_dump($message);
};
$example();

// Herdando valor da variável quando a função é definina,
// não quando é chamada
$message 'world';
$example();

// Reseta mensagem
$message 'hello';

// Herdando por referência
$example = function () use (&$message) {
    
var_dump($message);
};
$example();

// O valor modificado no escopo pai
// reflete quando a função é chamada
$message 'world';
$example();

// Closures também aceitam argumentos normais
$example = function ($arg) use ($message) {
    
var_dump($arg ' ' $message);
};
$example("hello");
?>

O exemplo acima irá imprimir algo similar à:

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"

A partir do PHP 8.0.0 a lista de variáveis herdadas no escopo podem incluir uma vírgula final, que será ignorada.

Herdar variáveis do escopo pai não é o mesmo que usar variáveis globais. Variáveis globais existem no escopo global, o qual é o mesmo não importa a função sendo executada. O escopo pai de um closure é a função no qual o closure foi declarado (não necessariamente a função a partir do qual ele foi chamado). Veja o exemplo a seguir:

Exemplo #4 Closures e escopo

<?php
// Um exemplo básico de carrinho de compras que contém uma lista de produtos
// e a quantidade de cada produto. Inclui um método que
// calcula o preço total dos itens no carrinho utilizando uma
// closure como 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($total2);;
    }
}

$my_cart = new Cart;

// Adiciona alguns itens no carrinho
$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
?>

Exemplo #5 Vinculação automática do $this

<?php

class Test
{
    public function 
testing()
    {
        return function() {
            
var_dump($this);
        };
    }
}

$object = new Test;
$function $object->testing();
$function();
    
?>

O exemplo acima irá imprimir:

object(Test)#1 (0) {
}

Quando declarada no contexto de uma classe, a classe corrente é automaticamente vinculada a ela, tornando $this disponível dentro do escopo da função. Se essa vinculação automática da classe corrente não for o comportamento esperado, funções anônimas estáticas podem ser utilizadas.

Funções anônimas estáticas

Funções anônimas podem ser declaradas estaticamente. Evita que a classe corrente seja automaticamente vinculada a ela. Objetos também podem não ser vinculadas a ela em tempo de execução.

Exemplo #6 Tentando utilizar o $this de dentro de uma função anônima estática

<?php

class Foo
{
    function 
__construct()
    {
        
$func = static function() {
            
var_dump($this);
        };
        
$func();
    }
};
new 
Foo();

?>

O exemplo acima irá imprimir:

Notice: Undefined variable: this in %s on line %d
NULL

Exemplo #7 Tentando vincular um objeto a uma função anônima estática

<?php

$func 
= static function() {
    
// corpo da função
};
$func $func->bindTo(new StdClass);
$func();

?>

O exemplo acima irá imprimir:

Warning: Cannot bind an instance to a static closure in %s on line %d

Changelog

Versão Descrição
7.1.0 Funções anônimas podem não incluir superglobals, $this, ou qualquer variável com o mesmo nome como um parâmetro.

Notas

Nota: É possível utilizar func_num_args(), func_get_arg() e func_get_args() dentro de closures.

add a note add a note

User Contributed Notes 17 notes

up
286
orls
11 years ago
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

?>
up
13
dexen dot devries at gmail dot com
3 years ago
Every instance of a lambda has own instance of static variables. This provides for great event handlers, accumulators, etc., etc.

Creating new lambda with function() { ... }; expression creates new instance of its static variables. Assigning a lambda to a variable does not create a new instance. A lambda is object of class Closure, and assigning lambdas to variables has the same semantics as assigning object instance to variables.

Example script: $a and $b have separate instances of static variables, thus produce different output. However $b and $c share their instance of static variables - because $c is refers to the same object of class Closure as $b - thus produce the same output.

#!/usr/bin/env php
<?php

function generate_lambda() : Closure
{
       
# creates new instance of lambda
   
return function($v = null) {
        static
$stored;
        if (
$v !== null)
           
$stored = $v;
        return
$stored;
    };
}

$a = generate_lambda();  # creates new instance of statics
$b = generate_lambda();  # creates new instance of statics
$c = $b;                                 # uses the same instance of statics as $b

$a('test AAA');
$b('test BBB');
$c('test CCC');  # this overwrites content held by $b, because it refers to the same object

var_dump([ $a(), $b(), $c() ]);
?>

This test script outputs:
array(3) {
  [0]=>
  string(8) "test AAA"
  [1]=>
  string(8) "test CCC"
  [2]=>
  string(8) "test CCC"
}
up
29
cHao
7 years ago
In case you were wondering (cause i was), anonymous functions can return references just like named functions can.  Simply use the & the same way you would for a named function...right after the `function` keyword (and right before the nonexistent name).

<?php
    $value
= 0;
   
$fn = function &() use (&$value) { return $value; };

   
$x =& $fn();
   
var_dump($x, $value);        // 'int(0)', 'int(0)'
   
++$x;
   
var_dump($x, $value);        // 'int(1)', 'int(1)'
up
26
erolmon dot kskn at gmail dot com
6 years ago
<?php
   
/*
    (string) $name Name of the function that you will add to class.
    Usage : $Foo->add(function(){},$name);
    This will add a public function in Foo Class.
    */
   
class Foo
   
{
        public function
add($func,$name)
        {
           
$this->{$name} = $func;
        }
        public function
__call($func,$arguments){
           
call_user_func_array($this->{$func}, $arguments);
        }
    }
   
$Foo = new Foo();
   
$Foo->add(function(){
        echo
"Hello World";
    },
"helloWorldFunction");
   
$Foo->add(function($parameterone){
        echo
$parameterone;
    },
"exampleFunction");
   
$Foo->helloWorldFunction(); /*Output : Hello World*/
   
$Foo->exampleFunction("Hello PHP"); /*Output : Hello PHP*/
?>
up
11
toonitw at gmail dot com
3 years ago
As of PHP 7.0, you can use IIFE(Immediately-invoked function expression) by wrapping your anonymous function with ().

<?php
$type
= 'number';
var_dump( ...( function() use ($type) {
    if (
$type=='number') return [1,2,3];
    else if (
$type=='alphabet') return ['a','b','c'];
} )() );
?>
up
15
john at binkmail dot com
4 years ago
PERFORMANCE BENCHMARK 2017!

I decided to compare a single, saved closure against constantly creating the same anonymous closure on every loop iteration. And I tried 10 million loop iterations, in PHP 7.0.14 from Dec 2016. Result:

a single saved closure kept in a variable and re-used (10000000 iterations): 1.3874590396881 seconds

new anonymous closure created each time (10000000 iterations): 2.8460240364075 seconds

In other words, over the course of 10 million iterations, creating the closure again during every iteration only added a total of "1.459 seconds" to the runtime. So that means that every creation of a new anonymous closure takes about 146 nanoseconds on my 7 years old dual-core laptop. I guess PHP keeps a cached "template" for the anonymous function and therefore doesn't need much time to create a new instance of the closure!

So you do NOT have to worry about constantly re-creating your anonymous closures over and over again in tight loops! At least not as of PHP 7! There is absolutely NO need to save an instance in a variable and re-use it. And not being restricted by that is a great thing, because it means you can feel free to use anonymous functions exactly where they matter, as opposed to defining them somewhere else in the code. :-)
up
6
derkontrollfreak+9hy5l at gmail dot com
7 years ago
Beware that since PHP 5.4 registering a Closure as an object property that has been instantiated in the same object scope will create a circular reference which prevents immediate object destruction:
<?php

class Test
{
    private
$closure;

    public function
__construct()
    {
       
$this->closure = function () {
        };
    }

    public function
__destruct()
    {
        echo
"destructed\n";
    }
}

new
Test;
echo
"finished\n";

/*
* Result in PHP 5.3:
* ------------------
* destructed
* finished
*
* Result since PHP 5.4:
* ---------------------
* finished
* destructed
*/

?>

To circumvent this, you can instantiate the Closure in a static method:
<?php

public function __construct()
{
   
$this->closure = self::createClosure();
}

public static function
createClosure()
{
    return function () {
    };
}

?>
up
6
rob at ubrio dot us
11 years ago
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();

?>
up
11
a dot schaffhirt at sedna-soft dot de
12 years ago
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,
up
8
simon at generalflows dot com
10 years ago
<?php

/*
* An example showing how to use closures to implement a Python-like decorator
* pattern.
*
* My goal was that you should be able to decorate a function with any
* other function, then call the decorated function directly:
*
* Define function:         $foo = function($a, $b, $c, ...) {...}
* Define decorator:        $decorator = function($func) {...}
* Decorate it:             $foo = $decorator($foo)
* Call it:                 $foo($a, $b, $c, ...)
*
* This example show an authentication decorator for a service, using a simple
* mock session and mock service.
*/

session_start();

/*
* Define an example decorator. A decorator function should take the form:
* $decorator = function($func) {
*     return function() use $func) {
*         // Do something, then call the decorated function when needed:
*         $args = func_get_args($func);
*         call_user_func_array($func, $args);
*         // Do something else.
*     };
* };
*/
$authorise = function($func) {
    return function() use (
$func) {
        if (
$_SESSION['is_authorised'] == true) {
           
$args = func_get_args($func);
           
call_user_func_array($func, $args);
        }
        else {
            echo
"Access Denied";
        }
    };
};

/*
* Define a function to be decorated, in this example a mock service that
* need to be authorised.
*/
$service = function($foo) {
    echo
"Service returns: $foo";
};

/*
* Decorate it. Ensure you replace the origin function reference with the
* decorated function; ie just $authorise($service) won't work, so do
* $service = $authorise($service)
*/
$service = $authorise($service);

/*
* Establish mock authorisation, call the service; should get
* 'Service returns: test 1'.
*/
$_SESSION['is_authorised'] = true;
$service('test 1');

/*
* Remove mock authorisation, call the service; should get 'Access Denied'.
*/
$_SESSION['is_authorised'] = false;
$service('test 2');

?>
up
4
ayon at hyurl dot com
4 years ago
One way to call a anonymous function recursively is to use the USE keyword and pass a reference to the function itself:

<?php
$count
= 1;
$add = function($count) use (&$add){
   
$count += 1;
    if(
$count < 10) $count = $add($count); //recursive calling
   
return $count;
};
echo
$add($count); //Will output 10 as expected
?>
up
6
Anonymous
12 years ago
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);
?>
up
2
jake dot tunaley at berkeleyit dot com
2 years ago
Beware of using $this in anonymous functions assigned to a static variable.

<?php
class Foo {
    public function
bar() {
        static
$anonymous = null;
        if (
$anonymous === null) {
           
// Expression is not allowed as static initializer workaround
           
$anonymous = function () {
                return
$this;
            };
        }
        return
$anonymous();
    }
}

$a = new Foo();
$b = new Foo();
var_dump($a->bar() === $a); // True
var_dump($b->bar() === $a); // Also true
?>

In a static anonymous function, $this will be the value of whatever object instance that method was called on first.

To get the behaviour you're probably expecting, you need to pass the $this context into the function.

<?php
class Foo {
    public function
bar() {
        static
$anonymous = null;
        if (
$anonymous === null) {
           
// Expression is not allowed as static initializer workaround
           
$anonymous = function (self $thisObj) {
                return
$thisObj;
            };
        }
        return
$anonymous($this);
    }
}

$a = new Foo();
$b = new Foo();
var_dump($a->bar() === $a); // True
var_dump($b->bar() === $a); // False
?>
up
6
mail at mkharitonov dot net
7 years ago
Some comparisons of PHP and JavaScript closures.

=== Example 1 (passing by value) ===
PHP code:
<?php
$aaa
= 111;
$func = function() use($aaa){ print $aaa; };
$aaa = 222;
$func(); // Outputs "111"
?>

Similar JavaScript code:
<script type="text/javascript">
var aaa = 111;
var func = (function(aaa){ return function(){ alert(aaa); } })(aaa);
aaa = 222;
func(); // Outputs "111"
</script>

Be careful, following code is not similar to previous code:
<script type="text/javascript">
var aaa = 111;
var bbb = aaa;
var func = function(){ alert(bbb); };
aaa = 222;
func(); // Outputs "111", but only while "bbb" is not changed after function declaration

// And this technique is not working in loops:
var functions = [];
for (var i = 0; i < 2; i++)
{
    var i2 = i;
    functions.push(function(){ alert(i2); });
}
functions[0](); // Outputs "1", wrong!
functions[1](); // Outputs "1", ok
</script>

=== Example 2 (passing by reference) ===
PHP code:
<?php
$aaa
= 111;
$func = function() use(&$aaa){ print $aaa; };
$aaa = 222;
$func(); // Outputs "222"
?>

Similar JavaScript code:
<script type="text/javascript">
var aaa = 111;
var func = function(){ alert(aaa); };
aaa = 222; // Outputs "222"
func();
</script>
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8
kdelux at gmail dot com
11 years ago
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();

?>
up
2
gabriel dot totoliciu at ddsec dot net
11 years ago
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.
up
2
mike at borft dot student dot utwente dot nl
9 years ago
Since it is possible to assign closures to class variables, it is a shame it is not possible to call them directly. ie. the following does not work:
<?php
class foo {

  public
test;

  public function
__construct(){
   
$this->test = function($a) {
      print
"$a\n";
    };
  }
}

$f = new foo();

$f->test();
?>

However, it is possible using the magic __call function:
<?php
class foo {

  public
test;

  public function
__construct(){
   
$this->test = function($a) {
      print
"$a\n";
    };
  }

  public function
__call($method, $args){
    if (
$this->{$method} instanceof Closure ) {
      return
call_user_func_array($this->{$method},$args);
    } else {
      return
parent::__call($method, $args);
    }
  }
}
$f = new foo();
$f->test();
?>
it
Hope it helps someone ;)
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