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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 callable 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. As of 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"

As of PHP 8.0.0, the list of scope-inherited variables may include a trailing comma, which will be ignored.

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($total2);
    }
}

$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) {
}

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

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.

Notes

Note: It is possible to use func_num_args(), func_get_arg(), and func_get_args() from within a closure.

add a note add a note

User Contributed Notes 17 notes

up
268
orls
10 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
8
dexen dot devries at gmail dot com
2 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"
}
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11
toonitw at gmail dot com
2 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
25
cHao
6 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
24
erolmon dot kskn at gmail dot com
5 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
2
jake dot tunaley at berkeleyit dot com
1 year 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
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
11 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
13
john at binkmail dot com
3 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
3
derkontrollfreak+9hy5l at gmail dot com
6 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
5
simon at generalflows dot com
9 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');

?>
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9
kdelux at gmail dot com
10 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();

?>
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4
Anonymous
11 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);
?>
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3
gabriel dot totoliciu at ddsec dot net
10 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.
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4
mail at mkharitonov dot net
6 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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3
mike at borft dot student dot utwente dot nl
8 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 ;)
up
1
ayon at hyurl dot com
3 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
?>
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