create_function

(PHP 4 >= 4.0.1, PHP 5, PHP 7)

create_functionCrear una función anónima (estilo lambda)

Descripción

create_function(string $args, string $code): string

Crea una función anónima desde los parámetros pasados, y devuelve un nombre único para ella.

Precaución

Esta función realiza internamente un eval() y como tal tiene los mismos problemas de seguridad que eval(). Además posee características malas de rendimiento y uso de memoria.

Si se usa 5.3.0 o superior, se debería usar en su lugar una función anónima nativa.

Parámetros

Normalmente estos parámetros serán pasados como una cadena entre comillas simples. La razón de usar comillas simples es proteger a los nombres de las variables de ser analizados, de otro modo, si se usan comillas dobles habrá necesidad de escapar los nombres de las variables, p.ej. \$avar.

args

Los argumentos de la función.

code

El código de la función.

Valores devueltos

Devuelve un nombre de función único como cadena, o false en caso de error.

Ejemplos

Ejemplo #1 Crear una función anónima con create_function()

Se puede usar esta función para, por ejemplo, crear una función desde información reunida en tiempo de ejecución:

<?php
$nuevafunc 
create_function('$a,$b''return "ln($a) + ln($b) = " . log($a * $b);');
echo 
"Nueva función anónima: $nuevafunc\n";
echo 
$nuevafunc(2M_E) . "\n";
// imprime
// Nueva función anónima: lambda_1
// ln(2) + ln(2.718281828459) = 1.6931471805599
?>

O quizás para tener una función gestora general que pueda aplicar un conjunto de operaciones a una lista de parámetros:

Ejemplo #2 Hacer una función de proceso general con create_function()

<?php
function procesar($var1$var2$farr)
{
    foreach (
$farr as $f) {
        echo 
$f($var1$var2) . "\n";
    }
}

// crear un puñado de funciones matemáticas
$f1 'if ($a >=0) {return "b*a^2 = ".$b*sqrt($a);} else {return false;}';
$f2 "return \"min(b^2+a, a^2,b) = \".min(\$a*\$a+\$b,\$b*\$b+\$a);";
$f3 'if ($a > 0 && $b != 0) {return "ln(a)/b = ".log($a)/$b; } else { return false; }';
$farr = array(
    
create_function('$x,$y''return "algo de trigonometría: ".(sin($x) + $x*cos($y));'),
    
create_function('$x,$y''return "una hipotenusa: ".sqrt($x*$x + $y*$y);'),
    
create_function('$a,$b'$f1),
    
create_function('$a,$b'$f2),
    
create_function('$a,$b'$f3)
    );

echo 
"\nUsar la primera matriz de funciones anónimas\n";
echo 
"parámetros: 2.3445, M_PI\n";
procesar(2.3445M_PI$farr);

// ahora hacer un puñado de funciones de proceso de cadenas
$garr = array(
    
create_function('$b,$a''if (strncmp($a, $b, 3) == 0) return "** \"$a\" '.
    
'y \"$b\"\n** ¡Para mí se parecen! (mirando los 3 primeros caracteres)";'),
    
create_function('$a,$b''; return "CRCs: " . crc32($a) . ", ".crc32($b);'),
    
create_function('$a,$b''; return "similar(a,b) = " . similar_text($a, $b, &$p) . "($p%)";')
    );
echo 
"\nUsar la segunda matriz de funciones anónimas\n";
procesar("Cuando los pájaros cantan""Cuando es de noche"$garr);
?>

El resultado del ejemplo sería:

Usar la primera matriz de funciones anónimas
parámetros: 2.3445, M_PI
algo de trigonometría: -1.6291725057799
una hipotenusa: 3.9199852871011
b*a^2 = 4.8103313314525
min(b^2+a, a^2,b) = 8.6382729035898
ln(a)/b = 0.27122299212594

Usar la segunda matriz de funciones anónimas
** "Cuando es de noche" y "Cuando los pájaros cantan"
** ¡Para mí se parecen! (mirando los 3 primeros caracteres)
CRCs: -725381282, 342550513
similar(a,b) = 11(45.833333333333%)

Pero quizás el uso más común de las funciones estilo lambda (anónimas) sea el de crear funciones de llamada de retorno, por ejemplo cuando se usa array_walk() o usort()

Ejemplo #3 Usar funciones anónimas como funciones de llamada de retorno

<?php
$av 
= array("el ""un ""ese ""este ");
array_walk($avcreate_function('&$v,$k''$v = $v . "mango";'));
print_r($av);
?>

El resultado del ejemplo sería:

Array
(
  [0] => el mango
  [1] => un mango
  [2] => ese mango
  [3] => este mango
)

una matriz de cadenas ordenada de más corta a más larga

<?php

$sv 
= array("pequeña""más larga""una gran cadena""esto es una 'señora' cadena");
print_r($sv);

?>

El resultado del ejemplo sería:

Array
(
  [0] => pequeña
  [1] => más larga
  [2] => una gran cadena
  [3] => esto es una 'señora' cadena
)

ordenarla de más larga a más corta

<?php

usort
($svcreate_function('$a,$b','return strlen($b) - strlen($a);'));
print_r($sv);

?>

El resultado del ejemplo sería:

Array
(
  [0] => esto es una 'señora' cadena
  [1] => una gran cadena
  [2] => más larga
  [3] => pequeña
)

Ver también

add a note

User Contributed Notes 22 notes

up
19
tamagochi_man
4 years ago
Whilst it was correct 11 years ago, the statement of Dan D is not so correct any moreю Anonymous functions are now objects of a class Closure and are safely collected by garbage collector.
up
4
Josh J
16 years ago
In regards to the recursion issue by info at adaniels dot nl

Anon function recursion by referencing the function variable in the correct scope.
<?php
$fn2
= create_function('$a', 'echo $a; if ($a < 10) call_user_func($GLOBALS["fn2"], ++$a);');
$fn2(1);
?>
up
16
Dan D
16 years ago
Beware when using anonymous functions in PHP as you would in languages like Python, Ruby, Lisp or Javascript.  As was stated previously, the allocated memory is never released; they are not objects in PHP -- they are just dynamically named global functions -- so they don't have scope and are not subject to garbage collection.

So, if you're developing anything remotely reusable (OO or otherwise), I would avoid them like the plague.  They're slow, inefficient and there's no telling if your implementation will end up in a large loop.  Mine ended up in an iteration over ~1 million records and quickly exhasted my 500MB-per-process limit.
up
2
kak dot serpom dot po dot yaitsam at gmail dot com
10 years ago
Try this to boost performance of your scripts (increase maxCacheSize):

<?php
runkit_function_copy
('create_function', 'create_function_native');
runkit_function_redefine('create_function', '$arg,$body', 'return __create_function($arg,$body);');

function
__create_function($arg, $body) {
    static
$cache = array();
    static
$maxCacheSize = 64;
    static
$sorter;

    if (
$sorter === NULL) {
       
$sorter = function($a, $b) {
            if (
$a->hits == $b->hits) {
                return
0;
            }

            return (
$a->hits < $b->hits) ? 1 : -1;
        };
    }

   
$crc = crc32($arg . "\\x00" . $body);

    if (isset(
$cache[$crc])) {
        ++
$cache[$crc][1];
        return
$cache[$crc][0];
    }

    if (
sizeof($cache) >= $maxCacheSize) {
       
uasort($cache, $sorter);
       
array_pop($cache);
    }

   
$cache[$crc] = array($cb = eval('return function('.$arg.'){'.$body.'};'), 0);
    return
$cb;
}
?>
up
1
kkaiser at revolution-records dot net
15 years ago
In the process of migrating a PHP4 codebase to PHP5, I ran into a peculiar problem. In the library, every class was derived from a generic class called 'class_container'. 'class_container' contained an array called runtime_functions and a method called class_function that was as follows:

<?php
function class_function($name,$params,$code) {

 
$this->runtime_functions[$name] = create_function($params,$code);

}
?>

In a subclass of class_container, there was a function that utilized class_function() to store some custom lambda functions that were self-referential:

<?php
function myfunc($name,$code) {

 
$this->class_function($name,'$theobj','$this=&$theobj;'.$code);

}
?>

In PHP4, this worked just fine. The idea was to write blocks of code at the subclass level, such as "echo $this->id;", then simply $MYOBJ->myfunc("go","echo $this->id;"); and later call it like $MYOBJ->runtime_functions["go"]();

It essentially worked exactly like binding anonymous functions to objects in Javascript.

Note how the "$this" keyword had to be manually redefined for the $code block to work.

In PHP5, however, you can't redeclare $this without getting a fatal error, so the code had to be updated to:

<?php
function myfunc($name,$code) {

 
$this->class_function($name,'$this',$code);

}
?>

Apparently create_function() allows you to set $this via a function argument, allowing you to bind anonymous functions to instantiated objects. Thought it might be useful to somebody.
up
1
info at adaniels dot nl
16 years ago
Note that using __FUNCTION__ in a an anonymous function, will always result '__lambda_func'.

<?php
    $fn
= create_function('', 'echo __FUNCTION__;');
   
$fn();
   
// Result: __lambda_func
   
echo $fn;
   
// Result: ºlambda_2 (the actual first character cannot be displayed)
?>

This means that a anonymous function can't be used recursively. The following code (recursively counting to 10) results in an error:
<?php
    $fn2
= create_function('$a', 'echo $a; if ($a < 10) call_user_func(__FUNCTION__, $a++);');
   
$fn2(1);
   
// Warning: call_user_func(__lambda_func) [function.call-user-func]: First argument is expected to be a valid callback in T:/test/test.php(21) : runtime-created function on line 1
?>
up
1
CertaiN
9 years ago
Best wapper:

<?php

function create_lambda($args, $code) {
    static
$func;
    if (!isset(
$func[$args][$code])) {
       
$func[$args][$code] = create_function($args, $code);
    }
    return
$func[$args][$code];
}
up
1
Dave H
11 years ago
The following function is very useful for creating an alias of a user function.
For built-in functions, it is less useful because default values are not available, so function aliases for built-in functions must have all parameters supplied, whether optional or not.

<?php
function create_function_alias($function_name, $alias_name)
{
    if(
function_exists($alias_name))
        return
false;
   
$rf = new ReflectionFunction($function_name);
   
$fproto = $alias_name.'(';
   
$fcall = $function_name.'(';
   
$need_comma = false;
   
    foreach(
$rf->getParameters() as $param)
    {
        if(
$need_comma)
        {
           
$fproto .= ',';
           
$fcall .= ',';
        }

       
$fproto .= '$'.$param->getName();
       
$fcall .= '$'.$param->getName();

        if(
$param->isOptional() && $param->isDefaultValueAvailable())
        {
           
$val = $param->getDefaultValue();
            if(
is_string($val))
               
$val = "'$val'";
           
$fproto .= ' = '.$val;
        }
       
$need_comma = true;
    }
   
$fproto .= ')';
   
$fcall .= ')';

   
$f = "function $fproto".PHP_EOL;
   
$f .= '{return '.$fcall.';}';

    eval(
$f);
    return
true;
}
?>
up
1
lombax85 at gmail dot com
1 year ago
For who *really* needs the create_function() on php8 (because of legacy code that cannot be changed easily) there is this: "composer require lombax85/create_function".
up
0
neo at nowhere dot com
14 years ago
In response to kkaiser at revolution-records dot net's note, even tho PHP will allow you to use
<?
$myfunc = create_function('$this', $code);
?>
You can NOT use a reference to "$this" inside of the anonymous function, as PHP will complain that you are using a reference to "$this" in a non-object context.

Currently, I have not found a work-around for this...
up
0
Alan FUNG
14 years ago
$f = create_function('','echo "function defined by create_function";');
$f();

result:
function defined by create_function

You may define no return in function body while you are using create_function.
up
0
Rene Saarsoo
14 years ago
Here has been some discussion about the "memory leak" create_function() can create.

What create_function() actually does, is creating an ordinary function with name chr(0).lambda_n where n is some number:

<?php
$f
= create_function('', 'return 1;');

function
lambda_1() { return 2; }

$g = "lambda_1";
echo
$g(); // outputs: 2

$h = chr(0)."lambda_1";
echo
$h(); // outputs: 1
?>
up
0
TSE-WebDesign
15 years ago
Here's how to call a runtime-created function from another runtime-created function:
<?php
        $get_func
= create_function('$func', 'return substr($func,1);');
       
$get_value = create_function('$index','return pow($index,$index);');
       
$another_func = create_function('$a', '$func="\x00"."'.$get_func($get_value).'";return $func($a);');
        echo
$another_func(2); # result is 4
?>
up
0
Phlyst
16 years ago
In reply to info at adaniels dot nl:

You may not be able to use __FUNCTION__ in a lambda (thanks for pointing it out; I was having that problem just now), but you can use $GLOBALS to work around it if you're assigning the function to a variable. I reimplemented array_walk_recursive() in PHP4 like this:

<?php
$array_walk_recursive
= create_function('&$array, $callback',
   
'foreach($array as $element) {
        if(is_array($element)) {
            $funky = $GLOBALS["array_walk_recursive"];
            $funky($element, $callback);
        }
        else {
            $callback($element);
        }
    }'
);
?>
up
0
josh at janrain dot com
16 years ago
Beware! This is merely a convenience function that generates a unique name for a regular function. It is *not* a closure or even an anonymous function. It is just a regular function that gets named for you.
up
0
Joshua E Cook
16 years ago
Functions created by create_function() cannot return a value by reference.  The function below creates a function that can.  The arguments are the same as create_function().  Note that these arguments are passed, unmodified, to eval(), so be sure that data passed in is sanitized.

<?php
/**
* create_ref_function
* Create an anonymous (lambda-style) function
* which returns a reference
* see http://php.net/create_function
*/
function
create_ref_function( $args, $code )
{
    static
$n = 0;

   
$functionName = sprintf('ref_lambda_%d',++$n);
   
   
$declaration = sprintf('function &%s(%s) {%s}',$functionName,$args,$body);
   
    eval(
$declaration);
   
    return
$functionName;
}
?>
up
0
boards at gmail dot com
16 years ago
If you were checking to see if a function is made properly, this would be a better way of checking:

<?php
$fnc
= @create_function('$arg1,$arg2,$arg3', 'return true;');
# make that function whatever you want
if (empty($fnc)) {
  die(
'Could not create function $fnc.');
}

# although, the follow will NOT work
if (empty(create_function('$arg', 'return $arg;'))) {
  die(
'Could not create anonymous function.');
}
# you would get an error regarding not being able to use a
# return value in writeable context (i.e. a return value is
# a const in C, and the function empty() doesn't use a
# const void* parameter
?>
up
0
MagicalTux at FF.ST
18 years ago
neo at gothic-chat d0t de wrote :
Beware of memory-leaks, the garbage-collection seems to 'oversee' dynamically created functions!

Not really...

In fact, PHP can not "unassign" functions. So if you create a function, it won't be deleted until the end of the script, even if you unset the variable containing its name.

If you need to change a part of a function everytime you run a loop, think of a way to make a more general function or try using eval :) (functions are made to be re-used. If you need to run your own piece of code once, eval is much better).
up
0
neo at gothic-chat d0t de
18 years ago
Beware of memory-leaks, the garbage-collection seems to 'oversee' dynamically created functions!

I used a function like this to replace special characters in links with their htmlentities:
<?php
$text
= preg_replace_callback (
   
"/(<(frame src|a href|form action)=\")([^\"]+)(\"[^>]*>)/i",
   
create_function (
       
'$matches',
       
'return $matches[1] . htmlentities ($matches[3]) . $matches[4];'
   
),
   
$text);
?>

After 1000 calls, the process used about 5MB more than before. In my situation this boosted up the memory-size of one PHP-process up to over 100MB!

In such cases, better store the function in a global variable.
up
0
DB on music_ml at yahoo dot com dot ar
19 years ago
[EDIT by danbrown AT php DOT net: Combined user-corrected post with previous (incorrect) post.]

You can't refer to a class variable from an anonymous function inside a class method using $this.  Anonymous functions don't inherit the method scope.  You'll have to do this:

<?php
class AnyClass {

var
$classVar = 'some regular expression pattern';

function
classMethod() {

  
$_anonymFunc = create_function( '$arg1, $arg2', 'if ( eregi($arg2, $arg1) ) { return true; } else { return false; } ' );

  
$willWork = $_anonymFunc('some string', $classVar);

}

}
?>
up
0
x-empt[a_t]ispep.cx
21 years ago
Create_function enables the ability to change the scope of functions.  You might have a class where it needs to define a GLOBAL function.  This is possible, like:

<?php
       
class blah {
                function
blah() {
                       
$z=create_function('$arg1string','return "function-z-".$arg1string;');
                       
$GLOBALS['z']=$z;
                }
        }
       
$blah_object=new blah;

       
$result=$GLOBALS['z']('Argument 1 String');
        echo
$result;
?>

Making a function escape it's defined scope can be useful in many situations.
up
-1
edgar at goodforall dot eu
13 years ago
Just a little toy I thought up, I would like to share. Creates an anonymous function, which let you use a class  as a function.

In php 5.3 there is support for real functors  (trough __invoke):

<?php
function createFunctor($className){
       
$content = "
                static \$class;
                if(!\$class){
                        \$class = new
$className;
                }
                return \$class->run(\$args);
        "
;
       
$f = create_function('$args', $content);
        return
$f;

}
class
test {
        public function
run($args){
                print
$args;
        }
}
$test = createFunctor('test');
$test('hello world');
?>
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