Variable functions

PHP supports the concept of variable functions. This means that if a variable name has parentheses appended to it, PHP will look for a function with the same name as whatever the variable evaluates to, and will attempt to execute it. Among other things, this can be used to implement callbacks, function tables, and so forth.

Variable functions won't work with language constructs such as echo(), print(), unset(), isset(), empty(), include(), require() and the like. You need to use your own wrapper function to utilize any of these constructs as variable functions.

Example 17-14. Variable function example

<?php function foo() { echo "In foo()<br />\n"; } function bar($arg = '') { echo "In bar(); argument was '$arg'.<br />\n"; } // This is a wrapper function around echo 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() ?>

You can also call an object's method by using the variable functions feature.
Example 17-15. Variable method example

<?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() ?>

User Contributed Notes
Variable functions

Storm
03-May-2005 10:34


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 09:33


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 07:14


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
02-May-2002 06:49


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
17-Mar-2002 11:11


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
13-Jan-2002 09:18


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"