Valori restituiti
It may be useful to note that 'variable functions' can only be used in conjunction with functions, and not language constructs such as echo, die, exit, etc.
Funzioni variabili
PHP supporta il concetto di funzioni variabili. Ciò significa che se un nome di variabile ha le parentesi accodate ad esso, PHP cercherà una funzione con lo stesso nome del valore della variabile, e cercherà di eseguirla. Tra le altre cose, ciò puo essere usato per implementare delle callbacks, tabelle di funzioni e così via.
Le funzioni variabili non funzionano con costrutti di linguaggio come echo(), print(), unset(), isset(), empty(), include(), require() e like. Occorre costruire una propria funzione per utilizzare questi costrutti come variabili per funzioni.
Example #1 Esempio di funzioni variabili
<?php
function foo() {
echo "In foo()<br />\n";
}
function bar($arg = '')
{
echo "In bar(); l'argomento era '$arg'.<br />\n";
}
// Questa è la funzione per usare echo
function echoit($string)
{
echo $string;
}
$func = 'foo';
$func(); // questa chiama foo()
$func = 'bar';
$func('test'); // questa chiama bar()
$func = 'echoit';
$func('test'); // questa chiama echoit()
?>
Tramite le funzioni variabili si può eseguire anche metodi di oggetti.
Example #2 Esempio di un metodo variabile
<?php
class Foo
{
function Variable()
{
$name = 'Bar';
$this->$name(); // Questo esegue il metodo Bar()
}
function Bar()
{
echo "This is Bar";
}
}
$foo = new Foo();
$funcname = "Variable";
$foo->$funcname(); // Questo esegue $foo->Variable()
?>
Vedere anche call_user_func(), variabili variabili e function_exists().
add a note
User Contributed NotesFunzioni variabili
mike at mike-griffiths dot co dot uk
27-Jun-2007 07:37
27-Jun-2007 07:37
boards at gmail dot com
22-Jan-2006 10:07
22-Jan-2006 10:07
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 08:34
03-May-2005 08:34
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;
$db->connect();
?>
Much easier than having multiple database classes or even extending a base class.
ian at NO_SPAM dot verteron dot net
20-Dec-2002 07:33
20-Dec-2002 07:33
A good method to pass around variables containing function names within some class is to use the same method as the developers use in preg_replace_callback - with arrays containing an instance of the class and the function name itself.
function call_within_an_object($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 05:14
05-Sep-2002 05:14
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 04:49
02-May-2002 04:49
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 09:11
17-Mar-2002 09:11
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 07:18
13-Jan-2002 07:18
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"