cannot define constructor as protected or private! why?
I've just created a simple test-file to confirm whether this happens on my machine too, and I think I've found the answer. Take the following code:
<?phperror_reporting( E_ALL | E_STRICT );class Foo { public function __construct( ) { }}class Bar extends Foo { protected function __construct( ) { }}
When trying to execute that code, I get a fatal error: "PHP Fatal error: Access level to Bar::__construct() must be public (as in class Foo) in /home/berry/foo.php on line 12." That means you can't change the access level in a child class, if the parent has already defined the access level, which actually makes a lot of sense: PHP wouldn't know which constructor to call, I guess.
As a side note: by looking at your code, B extends A, and A uses B. Why exactly is that so, it seems like a strange construction to me? I'm guessing you actually want is composition, not inheritance.
You can define a constructor as protected or private. This code compiles runs just fine since OOP was rewritten for PHP/5:
<?phpclass A{ public function __construct(){ echo 'Instance of A created' . PHP_EOL; }}class B{ protected function __construct(){ echo 'Instance of B created' . PHP_EOL; }}class C{ private function __construct(){ echo 'Instance of C created' . PHP_EOL; }}
Of course, private constructors prevent you from creating an instance with the new
keyword, but PHP will trigger a fatal error (it won't just stop running):
<?phpnew A; // OKnew B; // Fatal error: Call to protected B::__construct() from invalid contextnew C; // Fatal error: Call to private C::__construct() from invalid context
You can create custom static initiators:
<?phpclass FancyClass { public static function init() { new self(); } protected function __construct() { echo 'Instance created!'; }}# This will not work.new FancyClass();# But this will work.FancyClass::init();