PHP 8.0.24 Released!

create_function

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

create_functionCreate a function dynamically by evaluating a string of code

Warning

This function has been DEPRECATED as of PHP 7.2.0, and REMOVED as of PHP 8.0.0. Relying on this function is highly discouraged.

Description

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

Creates a function dynamically from the parameters passed, and returns a unique name for it.

Caution

This function internally performs an eval() and as such has the same security issues as eval(). It also has bad performance and memory usage characteristics, because the created functions are global and can not be freed.

A native anonymous function should be used instead.

Parameters

It is normally advisable to pass these parameters as single quoted strings. If using double quoted strings, variable names in the code need to be escaped carefully, e.g. \$somevar.

args

The function arguments, as a single comma-separated string.

code

The function code.

Return Values

Returns a unique function name as a string, or false on failure. Note that the name contains a non-printable character ("\0"), so care should be taken when printing the name or incorporating it in any other string.

Examples

Example #1 Creating a function dynamically, with create_function() or anonymous functions

You can use a dynamically created function, to (for example) create a function from information gathered at run time. First, using create_function():

<?php
$newfunc 
create_function('$a,$b''return "ln($a) + ln($b) = " . log($a * $b);');
echo 
$newfunc(2M_E) . "\n";
?>

Now the same code, using an anonymous function; note that the code and arguments are no longer contained in strings:

<?php
$newfunc 
= function($a,$b) { return "ln($a) + ln($b) = " log($a $b); };
echo 
$newfunc(2M_E) . "\n";
?>

The above example will output:

ln(2) + ln(2.718281828459) = 1.6931471805599

Example #2 Making a general processing function, with create_function() or anonymous functions

Another use could be to have general handler function that can apply a set of operations to a list of parameters:

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

// create a bunch of math functions
$farr = array(
    
create_function('$x,$y''return "some trig: ".(sin($x) + $x*cos($y));'),
    
create_function('$x,$y''return "a hypotenuse: ".sqrt($x*$x + $y*$y);'),
    
create_function('$a,$b''if ($a >=0) {return "b*a^2 = ".$b*sqrt($a);} else {return false;}'),
    
create_function('$a,$b'"return \"min(b^2+a, a^2,b) = \".min(\$a*\$a+\$b,\$b*\$b+\$a);"),
    
create_function('$a,$b''if ($a > 0 && $b != 0) {return "ln(a)/b = ".log($a)/$b; } else { return false; }')
);

echo 
"\nUsing the first array of dynamic functions\n";
echo 
"parameters: 2.3445, M_PI\n";
process(2.3445M_PI$farr);

// now make a bunch of string processing functions
$garr = array(
    
create_function('$b,$a''if (strncmp($a, $b, 3) == 0) return "** \"$a\" '.
        
'and \"$b\"\n** Look the same to me! (looking at the first 3 chars)";'),
    
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 
"\nUsing the second array of dynamic functions\n";
process("Twas brilling and the slithy toves""Twas the night"$garr);
?>

Again, here is the same code using anonymous functions. Note that variable names in the code no longer need to be escaped, because they are not enclosed in a string.

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

// create a bunch of math functions
$farr = array(
    function(
$x,$y) { return "some trig: ".(sin($x) + $x*cos($y)); },
    function(
$x,$y) { return "a hypotenuse: ".sqrt($x*$x $y*$y); },
    function(
$a,$b) { if ($a >=0) {return "b*a^2 = ".$b*sqrt($a);} else {return false;} },
    function(
$a,$b) { return "min(b^2+a, a^2,b) = " min($a*$a+$b$b*$b+$a); },
    function(
$a,$b) { if ($a && $b != 0) {return "ln(a)/b = ".log($a)/$b; } else { return false; } }
);

echo 
"\nUsing the first array of dynamic functions\n";
echo 
"parameters: 2.3445, M_PI\n";
process(2.3445M_PI$farr);

// now make a bunch of string processing functions
$garr = array(
    function(
$b,$a) { if (strncmp($a$b3) == 0) return "** \"$a\" " .
        
"and \"$b\"\n** Look the same to me! (looking at the first 3 chars)"; },
    function(
$a,$b) { return "CRCs: " crc32($a) . ", ".crc32($b); },
    function(
$a,$b) { return "similar(a,b) = " similar_text($a$b$p) . "($p%)"; }
);
echo 
"\nUsing the second array of dynamic functions\n";
process("Twas brilling and the slithy toves""Twas the night"$garr);
?>

The above example will output:

Using the first array of dynamic functions
parameters: 2.3445, M_PI
some trig: -1.6291725057799
a hypotenuse: 3.9199852871011
b*a^2 = 4.8103313314525
min(b^2+a, a^2,b) = 8.6382729035898
ln(a)/b = 0.27122299212594

Using the second array of dynamic functions
** "Twas the night" and "Twas brilling and the slithy toves"
** Look the same to me! (looking at the first 3 chars)
CRCs: 3569586014, 342550513
similar(a,b) = 11(45.833333333333%)

Example #3 Using dynamic functions as callback functions

Perhaps the most common use for dynamic functions is to pass them as callbacks, for example when using array_walk() or usort().

<?php
$av 
= array("the ""a ""that ""this ");
array_walk($avcreate_function('&$v,$k''$v = $v . "mango";'));
print_r($av);
?>

Converted to an anonymous function:

<?php
$av 
= array("the ""a ""that ""this ");
array_walk($av, function(&$v,$k) { $v $v "mango"; });
print_r($av);
?>

The above example will output:

Array
(
  [0] => the mango
  [1] => a mango
  [2] => that mango
  [3] => this mango
)

Sorting strings from longest to shortest with create_function():

<?php
$sv 
= array("small""a big string""larger""it is a string thing");
echo 
"Original:\n";
print_r($sv);
echo 
"Sorted:\n";
usort($svcreate_function('$a,$b','return strlen($b) - strlen($a);'));
print_r($sv);
?>

Converted to an anonymous function:

<?php
$sv 
= array("small""a big string""larger""it is a string thing");
echo 
"Original:\n";
print_r($sv);
echo 
"Sorted:\n";
usort($sv, function($a,$b) { return strlen($b) - strlen($a); });
print_r($sv);
?>

The above example will output:

Original:
Array
(
  [0] => small
  [1] => a big string
  [2] => larger
  [3] => it is a string thing
)
Sorted:
Array
(
  [0] => it is a string thing
  [1] => a big string
  [2] => larger
  [3] => small
)

add a note

User Contributed Notes 22 notes

up
19
tamagochi_man
3 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
15 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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