I have an anonymous function which is supposed to call itself. However, I have no variable or function name at hand, so I was hoping to find a function that could do return "this" in context of functions. Is there such a thing?
Here's an example:
$f = function() use($bar, $foo) {
// call this function again.
};
Calling like this:
call_user_func(__FUNCTION__);
Leads to this:
Warning: call_user_func() expects parameter 1 to be a valid callback,
function '{closure}' not found or invalid function name
If I try to put $f in the use-list, then it says the variable is not defined (because it is not yet).
__FUNCTION__ cannot be used in anonymous functions
Pass the variable holding the anonymous function as a reference in the 'use' clause....
$f = function() use($bar, $foo, &$f) {
$f();
};
Tip of the hat to this answer.
Okay, I found out the way to do this:
$f = function() use(&$f) {
$f();
};
$f();
The key thing is to pass $f as a reference. Thus PHP does not try to pass a value but a reference to a memory slot.
I have an anonymous function which is supposed to call itself.
I prefer to use call_user_func_array(__FUNCTION__, $params); when calling a recursive function.
As your example doesn't have any arguments then i guess call_user_func(__FUNCTION__); would be better suited.
You would expect and hope the following code would work but that would be too easy.
$bar = 10;
$foo = 0;
$f = function() use (&$bar,$foo) {
if($bar){ // condition needed to prevent infinite loop
echo $bar-- . PHP_EOL;
call_user_func(__FUNCTION__); // wont work
}
};
$f();
The __FUNCTION__ "Magic constant" is unavailable to closures so the code needs to be adapted to allow the passing of the function variable. we can make the function available by passing it as a regular argument or via the use statement.
Function passed as argument
$bar = 10;
$foo = 0;
$f = function( $__FUNCTION__ = null ) use (&$bar, $foo) {
if($__FUNCTION__ && $bar){
echo $bar-- . PHP_EOL;
call_user_func( $__FUNCTION__, $__FUNCTION__);
}
};
$f ( $f );
Function passed via use statement
$bar = 10;
$foo = 0;
$__FUNCTION__ = function() use (&$bar, $foo, &$__FUNCTION__) {
if($bar){
echo $bar-- . PHP_EOL;
call_user_func( $__FUNCTION__ );
}
};
$__FUNCTION__();
Working example, click edit-> ideone it! to re-run code.
http://www.php.net/manual/en/language.constants.predefined.php
Edit: Posted before code was given. Of course it doesn't work on anonymous functions.
call_user_func(__FUNCTION__, $param1, $param2);
call_user_func_array(__FUNCTION__, $params);
function i_dont_know() {
call_user_func(__FUNCTION__,$params);
//or
$funcname = __FUNCTION__;
$funcname($params);
}
Related
Is it a bad practice to use it?
Because people say that global variables are bad practice and the use thing brings variables from outside into the functions, so it's like global
This is how it looks
$a = 1;
$func = function() use($a){
print $a;
};
Any arguments defined in the "use" arguments for an anonymous function use the value at the time when the anonymous function is defined; so they must exist at that point; but they don't need to be passed (or even exist in the caller scope) when the function is called.
function myFunctionCreator() {
$a = 1; // Must exist for the `use` clause
$func = function() use($a){
echo $a, PHP_EOL;
};
return $func;
}
$myFunc = myFunctionCreator();
$a = 2;
$myFunc(); // echoes 1 (value of $a at the point where the function was created)
As you can see from the above example, $a has a value of 1 at the point where the function is defined, and even though a variable with the same name exists at the point when the function called, it is the original $a (with the value 1) that is used in the function call.
Arguments defined in the main argument definition need not exist when the function is defined, but the values must be passed as arguments to the function at the point when it is called.
function myFunctionCreator() {
$a = 1; // Need not exist, and will be ignored
$func = function($a) {
echo $a, PHP_EOL;
};
return $func;
}
$myFunc = myFunctionCreator();
$value = 2;
$myFunc($value); // echoes 2 (value of $a explicitly passed to the function call
// at the time it is executed)
So the behaviour of the two types is quite different, and their purpose when combined provides a degree of flexibility that is quite different
As Rizier123 has mentioned in his comment, arguments passed to an anonymous function as "standard" can have defaults, typehints, etc, whereas "use" arguments cannot.
function myFunctionCreator() {
$func = function(array $dataset = [1,2,3]) {
foreach($dataset as $value) {
echo $value, PHP_EOL;
}
};
return $func;
}
$myFunc = myFunctionCreator();
$value = ['a','b','c'];
$myFunc($value);
$myFunc();
$myFunc(['x','y','z']);
Or (as the third call shows, arguments can be passed directly.
Andy of these applied to a "use" argument will result in a parse error
Say I have a callable stored as a variable:
$callable = function($foo = 'bar', $baz = ...) { return...; }
How would I get 'bar'?
if (is_callable($callable)) {
return func_get_args();
}
Unfortunately func_get_args() is for the current function, is it possible to get a key value pair of arguments?
You can use reflection:
$f = new ReflectionFunction($callable);
$params = $f->getParameters();
echo $params[0]->getDefaultValue();
You may want to use get_defined_vars to accomplish this, this function will return an array of all defined variables, specifically by accessing the callable index from the output array.
I came across this question because I was looking for getting the arguments for a callable which is not just the function itself. My case is
class MyClass{
public function f(){
// do some stuff
}
}
$myclass = new MyClass();
$callable = array($myclass, "f);
This is a valid callback in php. In this case the solution given by #Marek does not work.
I worked around with phps is_callable function. You can get the name of the function by using the third parameter. Then you have to check whether your callback is a function or a (class/object) method. Otherwise the Reflection-classes will mess up.
if($callable instanceof Closure){
$name = "";
is_callable($callable, false, $name);
if(strpos($name, "::") !== false){
$r = new ReflectionMethod($name);
}
else{
$r = new ReflectionFunction($name);
}
}
else{
$r = new ReflectionFunction($callable);
}
$parameters = $r->getParameters();
// ...
This also returns the correct value for ReflectionFunctionAbstract::isStatic() even though the $name always uses :: which normally indicates a static function (with some exceptions).
Note: In PHP>=7.0 this may be easier using Closures. There you can do someting like
$closure = Closure::fromCallable($callable);
$r = new ReflectionFunction($closure);
You may also cause have to distinguish between ReflectionFunction and ReflectionMethod but I can't test this because I am not using PHP>=7.0.
For example, if I do this:
function bar(&$var)
{
$foo = function() use ($var)
{
$var++;
};
$foo();
}
$my_var = 0;
bar($my_var);
Will $my_var be modified? If not, how do I get this to work without adding a parameter to $foo?
No, they are not passed by reference - the use follows a similar notation like the function's parameters.
As written you achieve that by defining the use as pass-by-reference:
$foo = function() use (&$var)
It's also possible to create recursion this way:
$func = NULL;
$func = function () use (&$func) {
$func();
}
NOTE: The following old excerpt of the answer (Jun 2012) was written for PHP < 7.0. As since 7.0 (Dec 2015) the semantics of debug_zval_dump() changed (different zval handling) the refcount(?) output of it differs nowadays and are not that much saying any longer (integers don't have a refcount any longer).
Validation via the output by not displaying $my_var changed (from 0) still works though (behaviour).
You can validate that on your own with the help of the debug_zval_dump function (Demo):
function bar(&$var)
{
$foo = function() use ($var)
{
debug_zval_dump($var);
$var++;
};
$foo();
};
$my_var = 0;
bar($my_var);
echo $my_var;
Output:
long(0) refcount(3)
0
A full-through-all-scopes-working reference would have a refcount of 1.
Closures are, almost by definition, closed by value, not by reference. You may "use by reference" by adding an & in the argument list:
function() use (&$var)
This can be seen in example 3 in the anonymous functions manual page.
No, they are not passed by reference.
function foo(&$var)
{
$foo = function() use ($var)
{
$var++;
};
$foo();
}
$my_var = 0;
foo($my_var);
echo $my_var; // displays 0
function bar(&$var)
{
$foo = function() use (&$var)
{
$var++;
};
$foo();
}
$my_var = 0;
bar($my_var);
echo $my_var; // displays 1
What are the differences between closures in JS and closures in PHP? Do they pretty much work the same way? Are there any caveats to be aware of when writing closures in PHP?
One difference is how both cope with storing the context in which an anonymous function is executed:
// JavaScript:
var a = 1;
var f = function() {
console.log(a);
};
a = 2;
f();
// will echo 2;
// PHP
$a = 1;
$f = function() {
echo $a;
};
$a = 2;
$f();
// will result in a "PHP Notice: Undefined variable: a in Untitled.php on line 5"
To fix this notice you'll have to use the use syntax:
$a = 1;
$f = function() use ($a) {
echo $a;
};
$a = 2;
$f();
// but this will echo 1 instead of 2 (like JavaScript)
To have the anonymous function behave somehow like the JavaScript counterpart you'll have to use references:
$a = 1;
$f = function() use (&$a) {
echo $a;
};
$a = 2;
$f();
// will echo 2
I think this is the most striking difference between JavaScript and PHP closures.
Second difference is that every JavaScript closure has a this context available which means, that you can use this inside the closure itself (although it's often quite complicated to figure out what this actually refers to) - PHP's current stable version (PHP 5.3) does not yet support $this inside a closure, but PHP's upcoming version (PHP 5.4) will support $this binding and rebinding using $closure->bind($this) (See the Object Extension RFC for more info.)
Third difference is how both languages treat closures assigned to object properties:
// JavaScript
var a = {
b: function() {}
};
a.b(); // works
// PHP
$a = new stdClass();
$a->b = function() {};
$a->b(); // does not work "PHP Fatal error: Call to undefined method stdClass::b() in Untitled.php on line 4"
$f = $a->b;
$f(); // works though
The same is true if closures are assigned to properties in class definitions:
class A {
public $b;
public function __construct() {
$this->b = function() {};
}
public function c() {
$this->b();
}
}
$a = new A();
// neither
$a->b();
// nor
$a->c();
// do work
Fourth difference: JavaScript Closures are full fledged objects, wheres in PHP they are restricted objects. For instance, PHP Closures cannot have properties of their own:
$fn = function() {};
$fn->foo = 1;
// -> Catchable fatal error: Closure object cannot have properties
while in JavaScript you can do:
var fn = function() {};
fn.foo = 1;
fn.foo; // 1
Fifth difference: Returned closures can be immediately called upon in Javascript:
var fn = function() { return function() { alert('Hi');}}
fn()();
Not in PHP:
$fn = function() { return function() { echo('Hi');};};
$fn()(); // syntax error
The only thing I've found in PHP (that is totally cool and really handy!) is the ability to use them as getters and setters in classes which was always a nightmare to achieve before, JavaScript can be used in the same way but they do both act almost identically from what I've seen.
I'm not sure about the namespacing convention differences between the two but as #Rijk pointed out there is a section on the PHP website dedicated to them
<?php
class testing {
private $foo = 'Hello ';
public $bar = 'Bar';
#Act like a getter and setter!
public static $readout = function ($val = null) {
if (!empty($val)) {
testing::$readout = $val;
}
return testing::$readout;
}
}
They are also really great for...
Looping through items with a controller rather than a new for/each loop on the page
Great for supplying as arguments to functions/classes
Whats annoying about them is...
You can't typecast them, since they're just functions...
They do pretty much work the same way. Here's more information about the PHP implementation: http://php.net/manual/en/functions.anonymous.php
You can use a closure (in PHP called 'anonymous function') as a callback:
// return array of ids
return array_map( function( $a ) { return $a['item_id']; }, $items_arr );
and assign it to a variable:
$greet = function( $string ) { echo 'Hello ' . $string; }; // note the ; !
echo $greet('Rijk'); // "Hello Rijk"
Furthermore, anonymous function 'inherit' the scope in which they were defined - just as the JS implementation, with one gotcha: you have to list all variables you want to inherit in a use():
function normalFunction( $parameter ) {
$anonymous = function() use( $parameter ) { /* ... */ };
}
and as a reference if you want to modify the orignal variable.
function normalFunction( $parameter ) {
$anonymous = function() use( &$parameter ) { $parameter ++ };
$anonymous();
$parameter; // will be + 1
}
Is it possible to access outer local varialbe in a PHP sub-function?
In below code, I want to access variable $l in inner function bar. Declaring $l as global $l in bar doesn't work.
function foo()
{
$l = "xyz";
function bar()
{
echo $l;
}
bar();
}
foo();
You could probably use a Closure, to do just that...
Edit : took some time to remember the syntax, but here's what it would look like :
function foo()
{
$l = "xyz";
$bar = function () use ($l)
{
var_dump($l);
};
$bar();
}
foo();
And, running the script, you'd get :
$ php temp.php
string(3) "xyz"
A couple of note :
You must put a ; after the function's declaration !
You could use the variable by reference, with a & before it's name : use (& $l)
For more informations, as a reference, you can take a look at this page in the manual : Anonymous functions
You must use the use keyword.
$bar = function() use(&$l) {
};
$bar();
In the very very old PHP 5.2 and earlier this didn't work. The syntax you've got isn't a closure, but a definition of a global function.
function foo() { function bar() { } }
works the same as:
function foo() { include "file_with_function_bar.php"; }
If you execute function foo twice, PHP will complain that you've tried to re-define a (global) function bar.
You can read default value by:
function(){
return preg_match(
"yourVar = \d+"
, str_file_get_contents(functionFile)
, arrayToPutFieldsValue
);
}
If You would use two functons in the same time - it's like someone's using a spoon and You want to take a food from that spoon - You'll waste a food or some of You will starv.
Anyway - You would have to set a pointer somehow in a hard way.
It's impossible to get any field from other function or class without calling it to life.
Functions/methods are instance-like - they need to be called.
Share the common fields by accessing a global fields with synchronized functions.
function a()
{
function val1($arg=null)
{
static $a;
if ($arg !== null) $a = $arg;
else return $a;
}
function b()
{
val1('1234');
echo val1() . '<br>'; // shows: 1234
val1('my custom data');
echo val1() . '<br>'; // shows: my custom data
}
b();
}
a();
Used val1('my custom data') to set my value
Used val1() to get my value