Newsgroups: php.internals
Path: news.php.net
Xref: news.php.net php.internals:35799
Mailing-List: contact internals-help@lists.php.net; run by ezmlm
Received-SPF: error (pb1.pair.com: domain stefan-marr.de from 82.96.83.42 cause and error)
Message-ID: <47C314CA.3060605@stefan-marr.de>
Date: Mon, 25 Feb 2008 20:19:38 +0100
Reply-To: php@stefan-marr.de
User-Agent: Thunderbird 2.0.0.9 (Windows/20071031)
MIME-Version: 1.0
To: Stanislav Malyshev <stas@zend.com>
Cc: internals@lists.php.net
References: <001c01c87264$3c01b4e0$b4051ea0$@de> <698DE66518E7CA45812BD18E807866CE014A8D9D@us-ex1.zend.net> <A8D5F2E2-AAD0-45A7-8BFA-0A95DF42E514@pooteeweet.org> <342791187.20080225104951@marcus-boerger.de> <47C2D8C5.2000401@stefan-marr.de> <47C2E9A1.5090708@zend.com>
In-Reply-To: <47C2E9A1.5090708@zend.com>
Content-Type: text/plain; charset=ISO-8859-15; format=flowed
Content-Transfer-Encoding: 7bit
Subject: Re: [PHP-DEV] RFC: Traits for PHP
From: php@stefan-marr.de (Stefan Marr)

Hi,

Stanislav Malyshev schrieb:
> What I still don't understand it's how you can solve these conflicts at 
> all. I.e., suppose you have Counter API and DBConnection API on each of 
> which you have clean() method - for Counter it resets it to zero and for 
> DB it resets authentication details. How it is possible to resolve it in 
> any way so that resulting class would support both APIs?
Would exactly do you mean with API? And how would you solve this problem 
without traits? Traits can not solve stuff like colliding methods with 
colliding semantics in interfaces.

One solution would be to do the following:

trait Counter {
   public function clean() {
     $this->setCntValue(0);
   }
}

trait DBConnection {
   public function clean() { // one problem we probably should not
                             // discuss here is the naming, think it
			    // should be named resetCredentials
     $this->setCredentials(null);
   }
}

class DBCounter {
   use Counter {
     !clean,
     cleanCounter => clean
   }
   use DBConnection {
     !clean,
     resetCredentials => clean
   }
}

This would be a class reusing the behavior implemented in both traits, 
and this is the contribution of the traits idea. With mixins this 
wouldn't be possible and C++ multiple-inheritance would introduce fragility.

If DBCounter should implement ICounter and IDBConnection with each 
having a clean method, there is no meaningful possible implementation 
within a single class. Since the semantics of the two clean methods are 
not as near as it would be necessary.

and a

class DBCounter {
   use Counter {
     !clean,
     cleanCounter => clean
   }
   use DBConnection {
     !clean,
     resetCredentials => clean
   }
   public function clean() {
     $this->cleanCounter();
     $this->resetCredentials();
   }
}

would be a bit pointless, but possible...

Kind Regards
Stefan