note 99705 added to language.oop5.final
| From: | Baldurien at osu1 dot php dot net | Date: | Tue, 31 Aug 2010 20:37:51 +0000 |
| Subject: | note 99705 added to language.oop5.final | ||
| Groups: | php.notes | ||
| Request: | Send a blank email to php-notes+get-172212@lists.php.net to get a copy of this message | ||
"Note for Java developers: the 'final' keyword is not used for class constants in
PHP. We use the keyword 'const'."
http://php.net/manual/en/language.oop5.constants.php
This is more or less true, regardless of the fact that constant (being defined at class level or
not) in PHP are only scalar (int, string, etc) while in Java they may be pure object (ex:
java.awat.Color.BLACK). The only possible solution of having such kind of constant is :
<?php
class Bar {...}
class Foo {
public static $FOOBAR;
static function __init() {
static $init = false;
if ($init) throw new Exception('Constants were already initialized');
self::$FOOBAR = new Bar();
$init = true;
}
}
Foo::__init();
?>
That said, perhaps it is useless unless PHP automatically calls the __init() method.
However, one alternative that could be done in certain case is this :
<?php
function __autoload($className) {
... require the file where the class is ...
if (interface_exists($className, false)) return;
if (class_exists($className, false)) {
$rc = new ReflectionClass($className);
if (!$rc->hasMethod('__init')) return;
$m = $rc->getMethod('__init');
if (!($m->isStatic() && $m->isPrivate())) {
throw new Exception($className . ' __init() method must be private and static !');
}
$m->invoke(null);
return;
}
throw new Exception('Class or interface not found ' . $className);
}
?>
This can only work when one class is defined per file, since we are assured that __autoload() will
be called to load the file containing the class.
eg:
test2.php:
<?php
class B {
public static $X;
private static function __init() {
echo 'B', "\n";
self::$X = array(1, 2);
}
}
class A {
public static $Y;
private static function __init() {
echo 'A', "\n";
self::$Y = array(3, 4);
}
}
?>
test.php:
<?php
function __autoload($n) {
if ($n == 'A' || $n == 'B') require 'test2.php';
... do our __init() trick ...
}
var_dump(B::$X); // shows B, then array(2) (1, 2)
var_dump(A::$Y); // shows NULL.
?>
----
Server IP: 195.221.21.36
Probable Submitter: 90.35.242.215
----
Manual Page -- http://www.php.net/manual/en/language.oop5.final.php
Edit -- https://master.php.net/note/edit/99705
Del: integrated -- https://master.php.net/note/delete/99705/integrated
Del: useless -- https://master.php.net/note/delete/99705/useless
Del: bad code -- https://master.php.net/note/delete/99705/bad+code
Del: spam -- https://master.php.net/note/delete/99705/spam
Del: non-english -- https://master.php.net/note/delete/99705/non-english
Del: in docs -- https://master.php.net/note/delete/99705/in+docs
Del: other reasons-- https://master.php.net/note/delete/99705
Reject -- https://master.php.net/note/reject/99705
Search -- https://master.php.net/manage/user-notes.php