create_function()

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

Create an anonymous (lambda-style) function

说明

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

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

This function internally performs aneval()and as such has the same security issues aseval(). Additionally it has bad performance and memory usage characteristics.

If you are using PHP 5.3.0 or newer a nativeanonymous functionshould be used instead.

参数

Usually these parameters will be passed as single quote delimited strings. The reason for using single quoted strings, is to protect the variable names from parsing, otherwise, if you use double quotes there will be a need to escape the variable names, e.g.$avar.

$args

The function arguments.

$code

The function code.

返回值

Returns a unique function name as a string,orFALSEon error.

范例

Creating an anonymous function withcreate_function()

You can use this function, to (for example) create a function from information gathered at run time:

<?php
$newfunc = create_function('$a,$b', 'return "ln($a) + ln($b) = " . log($a * $b);');
echo "New anonymous function: $newfunc\n";
echo $newfunc(2, M_E) . "\n";
// outputs
// New anonymous function: lambda_1
// ln(2) + ln(2.718281828459) = 1.6931471805599
?>

Or, perhaps to have general handler function that can apply a set of operations to a list of parameters:

Making a general processing function withcreate_function()

<?php
function process($var1, $var2, $farr)
{
    foreach ($farr as $f) {
        echo $f($var1, $var2) . "\n";
    }
}
// create a bunch of math functions
$f1 = 'if ($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,$y', 'return "some trig: ".(sin($x) + $x*cos($y));'),
    create_function('$x,$y', 'return "a hypotenuse: ".sqrt($x*$x + $y*$y);'),
    create_function('$a,$b', $f1),
    create_function('$a,$b', $f2),
    create_function('$a,$b', $f3)
    );
echo "\nUsing the first array of anonymous functions\n";
echo "parameters: 2.3445, M_PI\n";
process(2.3445, M_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 anonymous functions\n";
process("Twas brilling and the slithy toves", "Twas the night", $garr);
?>

以上例程会输出：

Using the first array of anonymous 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 anonymous functions
** "Twas the night" and "Twas brilling and the slithy toves"
** Look the same to me! (looking at the first 3 chars)
CRCs: -725381282, 342550513
similar(a,b) = 11(45.833333333333%)

But perhaps the most common use for of lambda-style (anonymous) functions is to create callback functions, for example when usingarray_walk()orusort()

Using anonymous functions as callback functions

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

以上例程会输出：

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

an array of strings ordered from shorter to longer

<?php
$sv = array("small", "larger", "a big string", "it is a string thing");
print_r($sv);
?>

以上例程会输出：

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

sort it from longer to shorter

<?php
usort($sv, create_function('$a,$b','return strlen($b) - strlen($a);'));
print_r($sv);
?>

以上例程会输出：

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

参见

• Anonymous functions

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.

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.

Workaround is as follows:
<?php
class Foo {
  function setHandler($handlerName, $handlerCode) {
    $this->handlerFunctions[$handlerName] = create_function('&$self, $dataArr', $handlerCode);
// NOTE: $this not allowed here, using $self as replacement
  }
  function executeHandler($handlerName, $dataArr) {
    if($this->handlerFunctions[$handlerName]) {
        $this->handlerFunctions[$handlerName](&$this, $dataArr);
      }
   }
  function getConstantInfo($what) {
    return($what);
  }
}
$bla = new Foo;
$bla->setHandler("load", 'echo($self->getConstantInfo("name")."\n");');
$bla->executeHandler("load", array("foo" => "bar"));
?>

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.

The function takes as arguments the tree array, the category id on which i want the retrieval, and the depth level for which i would like the subcategories ids returned.
this saves me a LOT of time on large adjacency list trees.
<?php
$ctg_tree = array(
'1'=>array('parent_id'=>0,
      'children'=>array(
     '2'=>array('parent_id'=>1,
           'children'=>array(
           '3'=>array('parent_id'=>2))),
      '4'=>array('parent_id'=>1,
           'children'=>array(
           '5'=>array('parent_id'=>4),
           '6'=>array('parent_id'=>4))))));
function getSubCategories($ctg_tree, $id, $level = null) {
                
    $getBranchIds =
create_function(
'$tree, $ctg_id, $level = null, $arr = null,'.
' $push = false, $getBranchIds','
      if(!$arr) {
        $arr = array();
      }
      if(intval($level) && $push){
        $level--;
      }
      foreach($tree as $key=>$ctg) {
        if($push) {
          $arr[] = $key;
        }
        if($ctg_id == $key) {
          $start = true;
          $push = true;
        }
if(count($ctg[\'children\']) && (intval($level) || $level === null)) {
$getBranchIds(
$ctg[\'children\'],$ctg_id,$level,&$arr,$push,$getBranchIds
);
        }
        if($start) return $arr;
      }
      return $arr;');
return $getBranchIds(
$ctg_tree, $id, $level, null, false, $getBranchIds
);
  }
print_r(getSubCategories($ctg_tree, 4, 1));
?>
Array
(
  [0] => 5
  [1] => 6
)
print_r(getSubCategories($ctg_tree, 1, 1));
Array
(
  [0] => 2
  [1] => 4
)
<?php
print_r(getSubCategories($ctg_tree, 1));
?>
Array
(
  [0] => 2
  [1] => 3
  [2] => 4
  [3] => 5
  [4] => 6
)

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
?>

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
?>

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;
}
?>

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);
?>

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
?>

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];
}

How to save memory-space:
<?php
function create_lambda($args, $code) {
  static $list = array();
  $i = "{$args}\0{$code}";
  if (!isset($list[$i])) {
    $list[$i] = create_function($args, $code);
  }
  return $list[$i];
}

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;
}
?>

To avoid memory problems, when creating a dynamic function within loops, register it as a global variable, and check if it has already been set;
<?php
global $my_func;
if (!isset($my_func))
{
  $my_func = create_function($args, $code);
}
$my_func();
?>
That way you don't end up creating the same function twice (or a couple of million of times, as it happened to me...)

How do you use function which is created by create_function() as class method?
<?php
class Hoge {
 var $lamda;
 function set($lamda) {
  $this->lamda = $lamda;
 }
 function callLamda() {
  $func = $this->lamda;
  return $func();
 }
}
$newfunc = create_function('', 'echo "hoge<br>\n";');
$h = new Hoge;
$h->set( $newfunc );
$h->callLamda();
?>
It works fine. :-)

If you need to upgrade more than one `create_function` to anonymous function, I'm working on a tool that makes dev's life much easier and adaptable for new versions of anything in PHP.
It's tested on 30+ various (and really weird :)) cases, like:
  -$callback = create_function('$a', 'return "<cas:proxy>$a</cas:proxy>";');  
  +$callback = function ($a) {
  +  return "<cas:proxy>{$a}</cas:proxy>";
  +};
Includes concat (.), string quotes and inclined function calls:
  -$func = create_function('$atts, $content = null','return "<div class=\"' . $class_list . '\">" . do_shortcode($content) . "</div>";' );
  +$func = function ($atts, $content = null) use ($class_list) {
  +  return "<div class=\"{$class_list}\">" . do_shortcode($content) . "</div>";
  +};
Do you want to automate the hard work?
1. Instal Rector
  composer require rector/rector --dev
2. Create config
  # rector.yml
  services:
    Rector\Php\Rector\FuncCall\CreateFunctionToAnonymousFunctionRector: ~
3. Upgrade your Code
  vendor/bin/rector process src --config rector.yml --dry-run
  vendor/bin/rector process src --config rector.yml

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');
?>

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...

$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.

In response to koyama at hoge dot org (14-Dec-2000):
This does NOT create a new method - try adding this at the end:
<?php
if (function_exists($h->lamda)) {
  print "Its a function\n";
} else {
  print "No it isnt";
}
?>
It creates a function which $h->lamda points to.
Under PHP4 you could simply add an argument $this which meant it *behaved* like a method (though it existed in global scope) but with PHP5, you can't have a variable named $this in a function (which is rather irksome).
(and methinks the ant-bot challenge is taking the mickey - min(three, four)? !).

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);
    }
  }');
?>

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.

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;
}
?>

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
?>

<?php
# dynamically create html helper functions which take the args
# $string_contents, $optional_hash_of_options
# and return the contents wrapped in a tag
  
$html_funcs = Array(
  'table',
  'tr',
  'th',
  'td',
  'div',
  'span',
  'pre',
  'strong',
  'em'
);
$args = '$html, $options=Array()';
$code = '
 $o = ""; 
 foreach ($options as $a => $b) {
  $o .= " $a=\"$b\"";
 }
 return "<$tag$o>$html</$tag>";
';
foreach ($html_funcs as $key => $tag) {
  ${$tag} = create_function($args, "\$tag = '$tag'; $code");
}
# usage example:
print $table(
 $tr($th('heading').$td('this is the cell content')),
 Array('style'=>'border: 1px solid silver;')
);
?>

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.

[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);
 
 }
}
?>

A nice technique for building complex search patterns on lists, files or whatever is to build function combining functions like this:
<?php
function _not_($f) {
 return create_function('$x',
  "return !$f(\$x);");
}
function _and_($f, $g) {
 return create_function('$x',
  "return $f(\$x) && $g(\$x);");
}
?>
(similarly for _or_ and others...). Once you've built your matching primitives you can then build more complex matches into your script.
Unfortunately, as explained in (closed) bug #10721, the function names returned by create_function have a null byte at the front and this causes a parse error.
You can fix the definition like this:
<?php
function _not_($f) {
 $f = substr($f, 1);
 return create_function('$x',
  "return !call_user_func(chr(0).'$f', \$x)");
}
?>
The expression that re-builds the function name avoid the null being literally in the parsed string. If there is a better fix, please let me know.

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.

If you create a function that will only be used from an object context (i.e. you want a dynamic method that can then call methods from the original object, still maintaining access to the object's runtime values) then you can use the following functions I have created (ob_lambda_func and ob_lambda) to enable the dynamic function to easily call *public* methods on the object, in their runtime contexts:
<?php
/* the OB Lambda functions allow a lambda function to call a method from its callee's object */
if(!function_exists('ob_lambda_func')){
function ob_lambda_func($method, $args) {
  if((phpversion()+0)<5.1 || (substr(phpversion(),2)+0)<1.1)
    die("\nError: This script requires PHP v5.1.1+!\n");
  $bt=debug_backtrace();
  foreach($bt as $xsp) {
    if(isset($xsp['object'])) {
      if(!method_exists($xsp['object'], $method)) continue;
      return call_user_func_array(array($xsp['object'], $method), $args);
    }
  }
  if(!function_exists($method))
    die("\nOB: Internal Error! ($method)");
  return call_user_func_array($method, $args);
}}
if(!function_exists('ob_lambda')){
function ob_lambda($method) {
  return create_function('','$args=func_get_args(); return ob_lambda_func('.var_export($method, true).',$args);');
}}
/* Usage:
 *  For each callable method, store the results of ob_lambda('method_name')
 *  When a lambda function you call wants to access one of these methods,
 *  you need to pass it the result of ob_lambda for that method, the easiest
 *  way is to have one of the lambda functions arguments accept the result
 *    i.e.: $myFunc=ob_lambda('myMethod');
 *       $lf1=create_function('$func', '$func( ... args ... )');
 *       $lf1($myFunc);
 *  because create_function prepends a \0 to the function name, it is difficult
 *  to pass the result of ob_lambda to the target function without using an argument
 */
/* here is an example -- lambda function Foo::test can call Foo::Bar and Foo::Baz, and these */
class Foo {
  private $bar, $baz, $test;
  private $runtimeValue=0;
  function __construct() {
    $this->runtimeValue=rand();
    $this->bar=ob_lambda('Bar');
    $this->baz=ob_lambda('Baz');
    $this->test=create_function(
      '$bar, $baz',
      '$bar("Hello, World!"); $baz();'
    );
  }
  function Test() {
    $fn=$this->test;
    $fn($this->bar, $this->baz);
  }
  function Bar($a) {
    echo "$a: Bar ($this->runtimeValue)\n";
  }
  function Baz() {
    echo "and another! Baz ($this->runtimeValue)\n";
  }
}
$foo=new Foo();
// Foo::Bar("Testing Other Method"); <-- this causes fatal error
// (using $this when not in object context)
$foo->Test();
?>
This snippet (with test) shows how the lambda function $foo->test can call Foo::Bar and Foo::Baz without an explicit reference to the original object. The methods are run from their object context, and so can access the runtime-modified variable $foo->runtimeValue, which is set to a random number on construction.
The function definition for $foo->test is the following:
function ($bar, $baz) {
  $bar("Hello, World!");
  $baz;
}
As you can see, it is clean and simple, with no obvious artifacts from the use of OB Lambda
The expected output should be:
Hello, World!: Bar (440048505)
and another! Baz (440048505)
Or any other random number in place of 440048505
Make sure, before you change your code, that your target server has PHP 5.1.1+, or these functions won't work and will return an error!
Hope this helps anyone as much as it has me! :)

<?
function is_function( &$mixed )
{
  if ( is_object( $mixed ) ) {
    return ( $mixed instanceof Closure );
  } elseif( is_string( $mixed ) ) {
    return function_exists( $mixed );
  } else {
    return false;
  }
}
function myfunc(){}
$test = 123;
echo is_function( $test ); //will return false
$test = 'isset';
echo is_function( $test ); //will return false... it's not work with reserved :( ...
$test = 'myfunc';
echo is_function( $test ); //will return true
$test = create_function( '', 'echo 123;' );
echo is_function( $test ); //will return true
$test = function () { echo 123; };
echo is_function( $test ); //will return true
?>

I experimented a bit in creating a lambda function using a variable amount of arguments. While I couldn't find an efficient way to create a random bit of code, I was able to get it to behave as a front end for existing functions (as well as user-defined of course).
The code required me to use the dreaded eval() function to get it to use a variable amount of parameters, so be sure that all input is thoroughly cleaned if derived from the user.
<?php
  function run_function( $function )
  {
    // Get Arguments, Unset Exisitng Parameter
    $params = func_get_args();
    unset( $params[0] );
    if( ( $count = count( $params ) ) > 0 )
    {
      $args = '$a';
      $inc = 'b';
      // Create Argument String - Formats as '$a, $b, $c' Per Number of Arguments
      for( $x = 1; $x < $count; $x++ )
      {
        $args .= ', $' . $inc;
        $inc++;
      }
      // Create Lambda Function and Format Paramters
      $lambda = create_function( $args, 'return ' . $function . '(' . $args . ');' );
      $params = "'" . implode('\', \'', $params) . "'";
      // Build and Evaluate Function with Parameters
      $eval = '$return = $lambda(' . $params . ');';
      eval($eval);
      return $return;
    }
    else
    {
      return false;
    }
  }
?>
For most applications you would be better off calling the function normally. Perhaps this little proof of concept may find some use if adapted to work by someone who requires it.

For those who want to create closure with create_function, don't bother, you can't.
Use create_closure instead :p
<?php
//same thing as create_function, but returns a closure..( 5.4)
function create_closure($args, $body){
 return eval("return function($args){ {$body} };");
}
?>

Default values works:
<?php
$f = create_function('$a,$b=3', 'var_dump($a, $b);');
$f(1);
// output:
// int(1)
// int(3)
?>

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).

Sometimes it may be useful to create functions in a dynamic environment 
(f. e. in a daemon-like php script).
Normally declaring a function must be done once, which results in the problem, 
that in this special case modifying a function wouldn't have an effect until the script is reloaded. 
Maybe this code snipplet is useful 4 u.
File: "functions.inc"
<?php
function test($str) {
  echo $str;
}
?>
Dynamic FunctionHandler:
<?php
$FileName = "functions.inc";
$FileHandle = fopen($FileName,"r");
$FileContent = fread($FileHandle,filesize($FileName));
fclose($FileHandle);
preg_match_all("#function\ ?([a-zA-Z0-9-_]*)\ ?\((.*?)\)\ ?\{(.*?)\}#mixse",$FileContent,$Matches);
if ( is_array($Matches) && isset($Matches[0]) && count($Matches[0]) > 0 ) {
   foreach ( $Matches[0] as $key=>$val ) {
    $$Matches[1][$key] = create_function($Matches[2][$key],$Matches[3][$key]);
  }
}
?>
The Test:
<?php echo $test("test"); ?>
.. will echo "test";
Hans Kuhlen

for those who want to assign it's own name to a function consider this code:
<?php
$fname = 'hello';
$func = sprintf('
  function %s($v="") {
    Return "$v<BR>";
  }
',
$fname
);
eval($func);
echo $fname('Please print it.... please....');
?>
what it does is, 
: Creats a function as a string;
: Replaces the function name with $fname value;
: Converts the string into a REAL php code with eval()
: Calls the function using the variable function as declared before ($fname);
Simple, isn't it?
Can work well as an abstraction layer for portability and/or compatibility purposes
Maxim Maletsky
maxim@maxim.cx // PHPBeginner.com

Here is another tricky but usefull techynote, good for adding "plugin" to a existing class :
<?php
class Hoge {
  var $lamda;
  var $text;
  function set($lamda)
  {
    $this->lamda = $lamda;
  }
  function callLamda()
  {
    $func = $this->lamda;
    return $func($this);
  }
  function get()
  {
    return $this->text;
  }
}
$newfunc = create_function('&$class', 'echo $class->get();' );
$h = new Hoge;
$h->text = "Hi there !";
$h->set($newfunc);
$h->callLamda();
?>

I use this create_closure() in my work to seperate callbacks into Classes:
<?php
function create_closure($fun, $args, $uses)
     {$params=explode(',', $args.','.$uses);
     $str_params='';
     foreach ($params as $v)
         {$v=trim($v, ' &$');
          $str_params.='\''.$v.'\'=>&$'.$v.', ';
         }
     return "return function({$args}) use ({$uses}) {{$fun}(array({$str_params}));};";
     }
?>
example:
<?php
$loop->addPeriodicTimer(1, eval(create_closure('pop_message', '$timer', '$cache_key, $n, &$response, &$redis_client')));
function pop_message($params)
     {extract($params, EXTR_REFS);
     $redis_client->ZRANGE($cache_key, 0, $n)
              ->then(//normal
                  function($data) use ($cache_key, $n, &$timer, &$response, &$redis_client)
                  {//...
                  },
                  //exception
                  function ($e) use (&$timer, &$response, &$redis_client)
                  {//...
                  }
                 );
     }
?>