函数
在线手册：中文 英文
PHP手册

可变函数

PHP 支持可变函数的概念。这意味着如果一个变量名后有圆括号，PHP 将寻找与变量的值同名的函数，并且尝试执行它。可变函数可以用来实现包括回调函数，函数表在内的一些用途。

变量函数不能用于语言结构，例如 echo()，print()，unset()，isset()，empty()，include()，require() 以及类似的语句。需要使用自己的包装函数来将这些结构用作变量函数。

Example #1 可变函数示例

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

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

// 使用 echo 的包装函数
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()
?>

还可以利用可变函数的特性来调用一个对象的方法。

Example #2 可变方法范例

<?php
class Foo
{
    function Variable()
    {
        $name = 'Bar';
        $this->$name(); // This calls the Bar() method
    }

    function Bar()
    {
        echo "This is Bar";
    }
}

$foo = new Foo();
$funcname = "Variable";
$foo->$funcname();   // This calls $foo->Variable()

?>

请参阅 call_user_func()，可变变量和 function_exists()。

函数
在线手册：中文 英文
PHP手册
PHP手册 - N: 可变函数

用户评论:

Anonymous (27-Jun-2011 07:20)

$ 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()
?>

imurnane at internode on net (02-May-2011 11:05)

Create and call a dynamically named function

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

$$tmp();
?>

Outputs "foo"

michalmojz at gmail dot com (29-Jan-2011 09:51)

You can make dynamic functions as well.

For example

<?php
$myFunction = function() {
      echo 1;
};

if(is_callable($myFunction)) {
      $myFunction();
}
?>

AnonymousPoster at disposeamail dot com (03-May-2010 10:20)

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";
?>

boards at gmail dot com (22-Jan-2006 06:07)

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.
?>

Storm (03-May-2005 04:34)

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.

ian at NO_SPAM dot verteron dot net (20-Dec-2002 03:33)

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');

madeinlisboa at yahoo dot com (05-Sep-2002 01:14)

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");
}

msmith at pmcc dot com (03-May-2002 12:49)

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.

anpatel at NOSPAM_cbu dot edu (18-Mar-2002 05:11)

Yes interpolation can be very tricky. I suggest that you always use parenthesis, or curly brackets(whichever applies) to make your expression clear.

Dont ever depend on a language's expression parse preference order.

retro at enx dot org (14-Jan-2002 03:18)

Another way to have php parse a variable within an object as a function is to simply set a temporary variable to its value. For example:

$obj->myfunction = "foo";
$x = $obj->myfunction;
$x(); // calls the function named "foo"