Обращение к функциям через переменные
PHP поддерживает концепцию переменных функций. Это означает, что если к имени переменной присоединены круглые скобки, PHP ищет функцию с тем же именем, что и результат вычисления переменной, и пытается ее выполнить. Эту возможность можно использовать для реализации обратных вызовов, таблиц функций и множества других вещей.
Переменные функции не будут работать с такими языковыми конструкциями как echo, print, unset(), isset(), empty(), include, require и другими подобными им операторами. Вам необходимо реализовывать свою функцию-обертку (wrapper) для того, чтобы приведенные выше конструкции могли работать с переменными функциями.
Пример #1 Работа с функциями посредством переменных
<?php
function foo() {
echo "In foo()<br />\n";
}
function bar($arg = '')
{
echo "In bar(); argument was '$arg'.<br />\n";
}
// Функция-обертка для echo
function echoit($string)
{
echo $string;
}
$func = 'foo';
$func(); // Вызывает функцию foo()
$func = 'bar';
$func('test'); // Вызывает функцию bar()
$func = 'echoit';
$func('test'); // Вызывает функцию echoit()
?>
Вы также можете вызвать методы объекта, используя возможности PHP для работы с переменными функциями.
Пример #2 Обращение к методам класса посредством переменных
<?php
class Foo
{
function Variable()
{
$name = 'Bar';
$this->$name(); // Вызываем метод Bar()
}
function Bar()
{
echo "This is Bar";
}
}
$foo = new Foo();
$funcname = "Variable";
$foo->$funcname(); // Обращаемся к $foo->Variable()
?>
При вызове статических методов, вызов функции "сильнее" чем оператор доступа к статическому свойству:
Пример #3 Пример вызова переменного метода со статическим свойством
<?php
class Foo
{
static $variable = 'static property';
static function Variable()
{
echo 'Method Variable called';
}
}
echo Foo::$variable; // Это выведет 'static property'. Переменная $variable будет разрешена в нужной области видимости.
$variable = "Variable";
Foo::$variable(); // Это вызовет $foo->Variable(), прочитав $variable из этой области видимости.
?>
Смотрите также is_callable(), call_user_func(), Переменные переменные и function_exists().
Коментарии
$ wget http://www.php.net/get/php_manual_en.tar.gz/from/a/mirror
$ grep -l "\$\.\.\." php-chunked-xhtml/function.*.html
List of functions that accept variable arguments.
<?php
array_diff_assoc()
array_diff_key()
array_diff_uassoc()
array()
array_intersect_ukey()
array_map()
array_merge()
array_merge_recursive()
array_multisort()
array_push()
array_replace()
array_replace_recursive()
array_unshift()
call_user_func()
call_user_method()
compact()
dba_open()
dba_popen()
echo()
forward_static_call()
fprintf()
fscanf()
httprequestpool_construct()
ibase_execute()
ibase_set_event_handler()
ibase_wait_event()
isset()
list()
maxdb_stmt_bind_param()
maxdb_stmt_bind_result()
mb_convert_variables()
newt_checkbox_tree_add_item()
newt_grid_h_close_stacked()
newt_grid_h_stacked()
newt_grid_v_close_stacked()
newt_grid_v_stacked()
newt_win_choice()
newt_win_entries()
newt_win_menu()
newt_win_message()
newt_win_ternary()
pack()
printf()
register_shutdown_function()
register_tick_function()
session_register()
setlocale()
sprintf()
sscanf()
unset()
var_dump()
w32api_deftype()
w32api_init_dtype()
w32api_invoke_function()
wddx_add_vars()
wddx_serialize_vars()
?>
A small, but helpful note. If you are trying to call a static function from a different namespace, you must use the fully qualified namespace, even if they have the same top level namespace(s). For example if you have the following class to call:
<?php
namespace Project\TestClass;
class Test {
static function funcToCall() {
return "test";
}
}
?>
You must call it as:
<?php
namespace Project\OtherTestClass;
class OtherTest {
static function callOtherFunc() {
$func = '\Project\TestClass::funcToCall';
$func();
}
}
?>
and not:
<?php
class OtherTest {
static function callOtherFunc() {
$func = 'TestClass::funcToCall';
$func();
}
}
?>
While the documentation suggests that the use of a constant is similar to the use of a variable, there is an exception regarding variable functions. You cannot use a constant as the function name to call a variable function.
const DEBUGME ='func';
function func($s) { echo $s. "\n"; }
DEBUGME('abc'); // results in a syntax error
$call = DEBUGME;
$call('abc'); // does the job
But you can use a constant as an argument to a function. Here's a simple workaround when you need to call a variable constant function:
function dynamic($what, $with)
{
$what($with);
}
dynamic(DEBUGME, 'abc');
This makes sense to me to hide API's and/or long (complicated) static calls.
Enjoy!
<?php
/*
You might have found yourself at this php variable functions page because, like me, you wanted to pass functions
around like objects to client objects as you can in JavaScript. The issue I ran into was although
I could call a function using a variable like this " $v(); "...I could not do it like this " $obj->p() " where
'p' is a property containing the name of the method to call. Did not want to save my property off to a variable prior
to making my call: " $v = $obj->p; $v(); "; even if one finds a way, the below applies...
I credit this expanded work to this person: tatarynowicz at gmail dot com;
without them I would not have gotten here.
*/
interface iface_dynamic_members{
//Use of this interface enables type-hinting for objects that implement it.
public function __call($name, $args);
public function __set($name, $value);
public function quietly_fail():bool;
}
trait trait_has_dynamic_members{
//Implementing these magic methods in the form of a trait, frees the client object up
//so it can still inherit from a parent-class.
public function __call($name, $args) {
if (is_callable($this->$name)) {
return call_user_func($this->$name, $args);
}
else {
//Your dynamic-membered object can declare itself as willing to ignore non-existent method calls or not.
if($this->quietly_fail()===true){
echo 'Method does not exist, but I do not mind.';
}else{
echo 'Method does not exist, I consider this a bug.';
}
}
}
public function __set($name, $value) {
$this->$name = is_callable($value) ? $value->bindTo($this, $this): $value; //Assignment using ternary operator.
}
}
abstract class MBR_ATTR{
//A class full of attributes that objects can take on; abstract since not to be instantiated (If I could make it "final" as well, I would).
public static function is_a_walker(iface_dynamic_members $obj, ?string $walker_type='normal pace'){
$obj->walker_type = $walker_type;
$obj->walker_walk = function() {
return "I am walking {$this->walker_type}.";
};
}
public static function is_a_runner(iface_dynamic_members $obj, string $runner_type){
$obj->runner_type = $runner_type;
$obj->runner_run = function() {
return "I am running {$this->runner_type}.";
};
self::is_a_walker($obj); //If can run, also can walk.
}
}
class cls_partly_dynamic implements iface_dynamic_members{
use trait_has_dynamic_members;
public function quietly_fail():bool{
return true;
}
}
// Report all errors except E_NOTICE
error_reporting(E_ALL & ~E_NOTICE); //Enable all error-reporting except notices.
//----
//config runner object...
$obj_runner = new cls_partly_dynamic();
MBR_ATTR::is_a_runner($obj_runner, 'fast');
$obj_runner->runner_type = 'a bit slow';
//----
//config walker object...
$obj_walker = new cls_partly_dynamic();
MBR_ATTR::is_a_walker($obj_walker, 'slow');
$obj_walker->walker_type = 'super fast';
//----
//Do stuff...
echo 'walker in action...' . '<br>';
echo $obj_walker->walker_walk() . '<br>';
echo '<br>';
echo 'runner in action...' . '<br>';
echo $obj_runner->walker_walk() . '<br>';
echo $obj_runner->runner_run() . '<br>';
echo $obj_runner->xxx() . '<br>'; //Try calling a non-existent method.
//I would agree that the above approach/technique is not always ideal, particulary due to the loss of code-completion in your
//IDE of choice; I would tend to use this approach for dynamic-programming in response to the user dictating processing steps via a UI.
?>
If you are here looking for a function reference, this is NOT how to do it:
<?php
function func1(){ echo "hell0 1";}
$choice = func1; // no quotes
?>
It works, but $choice is not what you might think, a reference to a function. It is simply the name of the function as a string, written without (!) quotes.
It's the same as
<?php
$choice = "func1"; // with quotes
?>
You can do echo gettype($choice) to confirm.
So calling
<?php
$choice()
?>
is a variable-function for both cases, calling it by its name, not by reference.
Go via an assigned anonymous function to get a reference to the function:
<?php
$func1 = function(){ echo "hell0 1";}
$func1 = function(){ echo "hell0 2";}
?>
Now you can pass around the function like a first class object
<?php
$choice = $func1;
?>
or
<?php
$choice = $func2;
?>
and call it
<?php
$choice();
?>
If you want to pass around a class method, use the "Complex callables" from the manual, above. It's a call by name (not a reference), but since you can include the object you can still get the flexibility you want:
<?php
class C {
function k(){ echo "inside k";}
function j(){ echo "inside j"; return array($this,"k");}};
?>
You can use $this as the object in the first element of the array.
<?php
$c = new C;
$c->k();
inside k
$func = $c->j();
inside j
?>
And now, le moment supreme:
<?php
$func();
inside k
?>
<?php
static bar method works with statically or non statically wherese non static method could not work statically
//non static method
class myCls{
public function foo(){
echo "foo function";
}
static public function bar(){
echo "static bar function";
}
}
$a = new myCls;
$myf = "foo";
$a->$myf();//works
echo "\n";
$a = [new myCls,"foo"];//works
$a();
echo "\n";
//$a = ["myCls","foo"];//fatal error
//$a();
echo "\n";
//$a = "myCls::foo";//fatal error
//$a();
echo "\n";
//static method called with statically or nonstatically
$b = new myCls;
$myf = "bar";
$b->$myf();//works
echo "\n";
$b = [new myCls,"bar"];//works
$b();
echo "\n";
$b = "myCls::bar";//works
$b();
echo "\n";
$b = ["myCls","bar"];//works
$b();
echo "\n";