call_user_func
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
?>
create_function
(PHP 4 >= 4.0.1, PHP 5)
create_function — Crée une fonction anonyme (style lambda)
Description
string create_function
( string $args
, string $code
)
Crée une fonction anonyme, à partir des paramètres passés, et retourne un nom de fonction unique.
Liste de paramètres
Généralement, les arguments args sont présentés sous la forme d'une chaîne à guillemets simples, et la même recommandation vaut pour code . La raison de l'utilisation des guillemets simples est de protéger les noms de variables du remplacement par leur valeur. Si vous utilisez les guillemets doubles, n'oubliez pas d'échapper les noms de variables (i.e. \$avar).
- args
-
Les arguments de la fonction.
- code
-
Le code de la fonction.
Valeurs de retour
Retourne un nom de fonction unique, sous la forme d'une chaîne de caractères, ou FALSE si une erreur survient.
Exemples
Exemple #1 Création d'une fonction anonyme avec create_function()
Vous pouvez utiliser cette fonction pour (par exemple) créer une fonction à partir d'informations récoltées durant l'exécution :
<?php
$newfunc = create_function('$a,$b', 'return "ln($a) + ln($b) = " . log($a * $b);');
echo "Nouvelle fonction anonyme : $newfunc\n";
echo $newfunc(2, M_E) . "\n";
// affichera :
// Nouvelle fonction anonyme : lambda_1
// ln(2) + ln(2.718281828459) = 1.6931471805599
?>
Ou, pour pouvoir appliquer une fonction générique à une liste d'arguments.
Exemple #2 Traitement générique par fonction avec create_function()
<?php
function process($var1, $var2, $farr)
{
foreach ($farr as $f) {
echo $f($var1, $var2) . "\n";
}
}
// Création d'une série de fonction mathématiques
$f1 = 'if ($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,$y', 'return "un peu de trigo : ".(sin($x) + $x*cos($y));'),
create_function('$x,$y', 'return "une hypoténuse : ".sqrt($x*$x + $y*$y);'),
create_function('$a,$b', $f1),
create_function('$a,$b', $f2),
create_function('$a,$b', $f3)
);
echo "\nUtilisation de la première liste de fonctions anonymes\n";
echo "paramétres : 2.3445, M_PI\n";
process(2.3445, M_PI, $farr);
// Maintenant une liste de fonction sur chaîne de caractères
$garr = array(
create_function('$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 "similarité (a,b) = " . similar_text($a, $b, &$p) . "($p%)";')
);
echo "\nUtilisation de la seconde liste de fonctions anonymes\n";
process("Twas brilling and the slithy toves", "Twas the night", $garr);
?>
L'exemple ci-dessus va afficher :
Utilisation de la première liste de fonctions anonymes paramétres : 2.3445, M_PI un peu de trigo : -1.6291725057799 une hypoténuse : 3.9199852871011 b*a^2 = 4.8103313314525 min(b^2+a, a^2,b) = 8.6382729035898 ln(a/b) = 0.27122299212594 Utilisation de la seconde liste de fonctions anonymes ** "Twas the night" and "Twas brilling and the slithy toves" ** Ces chaînes se ressemblent ! (regardez les trois premiers caractères) CRCs : -725381282 , 1908338681 similarité (a,b) = 11(45.833333333333%)
Mais l'utilisation la plus courante des fonctions lambda est la fonction de callback, par exemple, lors de l'utilisation de array_walk() ou usort()
Exemple #3 Utilisation de fonctions anonymes comme fonction de callback
<?php
$av = array("la ", "une ", "cette ", "une certaine ");
array_walk($av, create_function('&$v,$k', '$v = $v . "maison";'));
print_r($av);
?>
L'exemple ci-dessus va afficher :
Array ( [0] => la maison [1] => une maison [2] => cette maison [3] => une certaine maison )
un tableau de chaînes de caractères ordonnées de la plus courte à la plus longue
<?php
$sv = array("petite", "longue", "une très longue chaîne", "une phrase toute entière");
print_r($sv);
?>
L'exemple ci-dessus va afficher :
Array ( [0] => petite [1] => longue [2] => une très longue chaîne [3] => une phrase toute entière )
ordonnées de la plus longue à la plus courte
<?php
usort($sv, create_function('$a,$b','return strlen($b) - strlen($a);'));
print_r($sv);
?>
L'exemple ci-dessus va afficher :
Array ( [0] => une phrase toute entière [1] => une très longue chaîne [2] => longue [3] => petite )
add a note
User Contributed Notescreate_function
Rene Saarsoo
06-Feb-2008 11:31
06-Feb-2008 11:31
colin dot mckinnon at gmail dot com
20-Aug-2007 02:51
20-Aug-2007 02:51
In response to koyama at hoge dot org (14-Dec-2000):
This does NOT create a new method - try adding this at the end:
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)? !).
TSE-WebDesign
18-Aug-2007 06:55
18-Aug-2007 06:55
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 $another_func(2); # result is 4
?>
kkaiser at revolution-records dot net
13-Apr-2007 10:10
13-Apr-2007 10:10
In the process of migrating a PHP4 codebase to PHP5, I ran into a peculiar problem. In the library, every class was derived from a generic class called 'class_container'. 'class_container' contained an array called runtime_functions and a method called class_function that was as follows:
function class_function($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:
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 $this without getting a fatal error, so the code had to be updated to:
function myfunc($name,$code) {
$this->class_function($name,'$this',$code);
}
Apparently create_function() allows you to set $this via a function argument, allowing you to bind anonymous functions to instantiated objects. Thought it might be useful to somebody.
a dot steenveld at id dot umcn dot nl
18-Jan-2007 03:18
18-Jan-2007 03:18
It is possible to use this call to implement continuations but you need a small workaround for a nagging feature of create_function(). The result of this function does start with a null character which might result in loosing the name of your function altogether!. (See also bug report #40160)
Here is a bit of code to play with. The result should be 'f(2, 2) = 6'
<?php
/* continuations in php.
vim:nu
Code inspired by http://www.ps.uni-sb.de/~duchier/python/continuations.html
*/
function writeln($s) { echo "$s\n"; }
function lambda0 ($args, $code)
{ return substr(create_function ($args, $code), 1);
}
function L ($l)
{ if (strncmp($l, 'lambda_', 7) === 0) return "\0$l";
else return $l;
}
function mul ($x, $y, $c) { $f = L($c); $f($x*$y); }
function add ($x, $y, $c) { $f = L($c); $f($x+$y); }
function mal ($x, $y, $c) { mul(2, $x, lambda0 ('$v', "add(\$v, $y, $c);")); }
function f($x, $y)
{ mal($x, $y, lambda0 ('$v', "writeln(\"f($x, $y) = \$v\");"));
}
f(2, 2);
?>
Dan D
24-Oct-2006 04:22
24-Oct-2006 04:22
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.
Phlyst
06-Oct-2006 02:10
06-Oct-2006 02:10
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);
}
}');
?>
Josh J
27-Sep-2006 09:45
27-Sep-2006 09:45
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);
?>
info at adaniels dot nl
11-May-2006 12:42
11-May-2006 12:42
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
?>
josh at janrain dot com
03-Mar-2006 07:21
03-Mar-2006 07:21
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.
Joshua E Cook
20-Jan-2006 01:43
20-Jan-2006 01:43
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;
}
?>
boards at gmail dot com
31-Dec-2005 08:18
31-Dec-2005 08:18
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
?>
david [at] davelee.com.au
13-Apr-2005 11:15
13-Apr-2005 11:15
# 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;')
);
endofyourself at yahoo dot com
07-Oct-2004 09:17
07-Oct-2004 09:17
You really should avoid using this as well as you should avoid using eval(). Not only will there be a performance decrease but can it lead to obfuscation and bad coding habits. There is almost always an alternative solution to self modifying code.
MagicalTux at FF.ST
09-Mar-2004 07:25
09-Mar-2004 07:25
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).
neo at gothic-chat d0t de
21-Jan-2004 05:54
21-Jan-2004 05:54
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];'
),
$text);
?>
After 1000 calls, the process used about 5MB more than before. In my situation this boosted up the memory-size of one PHP-process up to over 100MB!
In such cases, better store the function in a global variable.
nospam at fiderallalla dot de
08-Aug-2003 03:39
08-Aug-2003 03:39
Sometimes it may be useful to create functions in a dynamic environment
(f. e. in a daemon-like php script).
Normally declaring a function must be done once, which results in the problem,
that in this special case modifying a function wouldn't have an effect until the script is reloaded.
Maybe this code snipplet is useful 4 u.
File: "functions.inc"
<?php
function test($str) {
echo $str;
}
?>
Dynamic FunctionHandler:
<?
$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
DB on music_ml at yahoo dot com dot ar
02-Apr-2003 02:58
02-Apr-2003 02:58
What I posted above is logical because 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);
}
}
?>
DB on music_ml at yahoo dot com dot ar
02-Apr-2003 12:04
02-Apr-2003 12:04
Apparently you can't refer to a class variable from an anonymous-defined function, inside a class method, using the $this keyword:
<?php
class AnyClass {
var $classVar = 'some regular expression pattern';
function classMethod() {
$_anonymFunc = create_function( '$arg', 'if ( eregi($this->classVar, $arg) ) { return true; } else { return false; } ' );
$wontWork = $_anonymFunc('some string');
}
}
?>
This would throw a warning on 'undefined variable: this'...
listes at brissambre dot org
14-Aug-2002 07:22
14-Aug-2002 07:22
[Editor's note: Only regular variables are serialized (scalars, arrays, objects), and as lambda functions are not stored as any of those types, it is not saved during session serialization.]
Warning, it seems that you can't store such lambda functions in Sessions, because only the function's name will be stored, not the function itself.
So don't save the function but only it's code and call create_function each time the script is called.
ben-php at bacarisse dot btinternet dot co dot uk
26-Jul-2001 10:33
26-Jul-2001 10:33
A nice technique for building complex search patterns on lists, files or whatever is to build function combining functions like this:
<?php
function _not_($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.
x-empt[a_t]ispep.cx
05-Jul-2001 08:41
05-Jul-2001 08:41
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.
maxim at maxim dot cx
28-Apr-2001 12:26
28-Apr-2001 12:26
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
mrben at free dot fr
21-Feb-2001 05:33
21-Feb-2001 05:33
Here is another tricky but usefull techynote, good for adding "plugin" to a existing class :
<?
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();
?>
koyama at hoge dot org
14-Dec-2000 01:22
14-Dec-2000 01:22
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. :-)