可変関数

PHP は可変関数(variable functions)の概念をサポートします。 これにより、変数名の後に括弧が付いている場合、その値が何であろうと PHPは、同名の関数を探し実行を試みます。 この機能は、コールバック、関数テーブル等を実装するために使用可能です。

可変関数は、echo, print, isset(), empty(), include, require のような言語構造と組み合わせて使用する ことはできません。これらの言語構造を可変変数として使うには 独自のラッパー関数を使う必要があります。

例1 可変関数の例

<?php
function foo()
{
    echo 
"In foo()<br />\n";
}

function 
bar($arg '')
{
    echo 
"In bar(); argument was '$arg'.<br />\n";
}

// これは、echo のラッパー関数です。
function echoit($string)
{
    echo 
$string;
}

$func 'foo';
$func();        // This calls foo()

$func 'bar';
$func('test');  // This calls bar()

$func 'echoit';
$func('test');  // This calls echoit()
?>

オブジェクトのメソッドを可変関数を使ってコールすることもできます。

例2 可変メソッドの例

<?php
class Foo
{
    function 
Variable()
    {
        
$name 'Bar';
        
$this->$name(); // Bar() メソッドのコール
    
}
    
    function 
Bar()
    {
        echo 
"This is Bar";
    }
}

$foo = new Foo();
$funcname "Variable";
$foo->$funcname();  // $foo->Variable() をコールする

?>

静的メソッドをコールするときには、関数呼び出しのほうが静的プロパティ演算子よりも優先されます。

例3 静的プロパティを含む可変メソッドの例

<?php
class Foo
{
    static 
$variable 'static property';
    static function 
Variable()
    {
        echo 
'Method Variable called';
    }
}

echo 
Foo::$variable// これは 'static property' を表示します。このスコープにおいて $variable が必要です。
$variable "Variable";
Foo::$variable();  // これは $foo->Variable() をコールします。このスコープでの $variable の内容を読むからです。

?>

is_callable()call_user_func()可変変数、そして function_exists()も参照してください。

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User Contributed Notes 8 notes

up
5
ian at NO_SPAM dot verteron dot net
11 years ago
A good method to pass around variables containing function names within some class is to use the same method as the developers use in preg_replace_callback - with arrays containing an instance of the class and the function name itself.

function call_within_an_object($fun)
{
  if(is_array($fun))
  {
    /* call a function within an object */
    $fun[0]->{$fun[1]}();
  }
  else
  {
    /* call some other function */
    $fun();
  }
}

function some_other_fun()
{
  /* code */
}

class x
{
  function fun($value)
  {
    /* some code */
  }
}

$x = new x();

/* the following line calls $x->fun() */
call_within_an_object(Array($x, 'fun'));

/* the following line calls some_other_fun() */
call_within_an_object('some_other_fun');
up
2
madeinlisboa at yahoo dot com
11 years ago
Finally, a very easy way to call a variable method in a class:

Example of a class:

class Print() {
    var $mPrintFunction;

    function Print($where_to) {
        $this->mPrintFunction = "PrintTo$where_to";
    }

    function PrintToScreen($content) {
        echo $content;
    }

    function PrintToFile($content) {
        fputs ($file, $contents);
    }

.. .. ..

    // first, function name is parsed, then function is called
    $this->{$this->mPrintFunction}("something to print");
}
up
0
boards at gmail dot com
8 years ago
If you want to call a static function (PHP5) in a variable method:

Make an array of two entries where the 0th entry is the name of the class to be invoked ('self' and 'parent' work as well) and the 1st entry is the name of the function.  Basically, a 'callback' variable is either a string (the name of the function) or an array (0 => 'className', 1 => 'functionName').

Then, to call that function, you can use either call_user_func() or call_user_func_array().  Examples:

<?php
class A {

  protected
$a;
  protected
$c;

  function
__construct() {
   
$this->a = array('self', 'a');
   
$this->c = array('self', 'c');
  }

  static function
a($name, &$value) {
    echo
$name,' => ',$value++,"\n";
  }

  function
b($name, &$value) {
   
call_user_func_array($this->a, array($name, &$value));
  }

  static function
c($str) {
    echo
$str,"\n";
  }

  function
d() {
   
call_user_func_array($this->c, func_get_args());
  }

  function
e() {
   
call_user_func($this->c, func_get_arg(0));
  }

}

class
B extends A {

  function
__construct() {
   
$this->a = array('parent', 'a');
   
$this->c = array('self', 'c');
  }

  static function
c() {
   
print_r(func_get_args());
  }

  function
d() {
   
call_user_func_array($this->c, func_get_args());
  }

  function
e() {
   
call_user_func($this->c, func_get_args());
  }

}

$a =& new A;
$b =& new B;
$i = 0;

A::a('index', $i);
$a->b('index', $i);

$a->c('string');
$a->d('string');
$a->e('string');

# etc.
?>
up
-1
Anonymous
3 years ago
$ 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()
?>
up
-2
Storm
9 years ago
This can quite useful for a dynamic database class:

(Note: This just a simplified section)

<?php
class db {

    private
$host = 'localhost';
    private
$user = 'username';
    private
$pass = 'password';
    private
$type = 'mysqli';
   
    public
$lid = 0;

   
// Connection function
   
function connect() {
       
$connect = $this->type.'_connect';
           
        if (!
$this->lid = $connect($this->host, $this->user, $this->pass)) {
            die(
'Unable to connect.');
        }
}
}
$db  = new db;
$db->connect();
?>

Much easier than having multiple database classes or even extending a base class.
up
-5
msmith at pmcc dot com
12 years ago
Try the call_user_func() function.  I find it's a bit simpler to implement, and at very least makes your code a bit more readable... much more readable and simpler to research for someone who isn't familiar with this construct.
up
-8
imurnane at internode on net
3 years ago
Create and call a dynamically named function

<?php
$tmp
= "foo";
$
$tmp = function() {
    global
$tmp;
    echo
$tmp;
};

$
$tmp();
?>

Outputs "foo"
up
-8
AnonymousPoster at disposeamail dot com
4 years ago
Variable functions allows higher-order programming.

Here is the classical map example.

<?php
/*
* Map function. At each $element of the $list, calls $fun([$arg1,[$arg2,[...,]],$element,$accumulator),
*      stores the return value into $accumulator for the next loop. Returns the last return value of the function,
*
* Notes : uses call_user_func_array() so passing parameters doesn't depend on $fun signature
*          It also returns FALSE upon error.
*          Please check the php documentation for more information
*/
function map($fun, $list,$params=array()){
   
$acc=NULL;
   
$last=array_push($params, NULL,$acc)-1; // alloc $element and $acc at the end
   
foreach($list as $params[$last-1]){
       
$params[$last]=call_user_func_array($fun , $params  );
    }
   
$acc=array_pop($params);
    return
$acc;
}

function
add($element,$acc){ // maybe only with multi-length function
   
if ($acc == NULL);
    return
$acc=$element+$acc;
}

$result=0;
$result=addTo($result,1);
$result=addTo($result,2);
$result=addTo($result,3);
echo
"result = $result\n";

$result=0;
$result=map('addTo',array(1,2,3));
echo
"result= $result\n";
?>
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