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Date: Sun, 23 Oct 2011 16:28:16 -0700
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To: Anthony Ferrara <ircmaxell@gmail.com>
Subject: Re: [PHP-DEV] Revisit: Traits requiring composing class to implement interface
From: php@stefan-marr.de (Stefan Marr)

Hi Anthony:

I will not comment on the original question of this thread, but felt =
obliged to point out some details where my understanding differs from =
what I understand from your explanation.=20

On 22 Oct 2011, at 07:25, Anthony Ferrara wrote:

> Well, I have a few opinions on this that I think are worth sharing:
>=20
> 1. If this change is made, we no longer would have mixins, but would
> have regular multiple-inheritance (With all the "issues" associated
> with it).  Note that I said mixins and not traits.  That's because
> since these were implemented with state (member properties), they are
> not traits as implemented, but regular mixins. (Yet another gripe, but
> that's slightly off topic).

Please refer to: =
https://wiki.php.net/rfc/horizontalreuse#handling_of_propertiesstate

"Traits do not provide any provisioning for handling state."

What you observe is that PHP is a very dynamic language when it comes to =
the definition of fields.
And that is what traits also take into account. We do the minimal =
possible thing, to keep the WTF factor low, but there is no "real" =
support for state.
And as someone else pointed out: the main difference is indeed the =
difference between linear application (mixins) and order-less =
composition (traits).


> There's a much bigger problem though.  How would you solve the problem
> where a class uses a trait that implements an interface, but you don't
> pull one of the methods through (for example, you exclude it in the
> use clause)?

The relevant part of the RFC: =
https://wiki.php.net/rfc/horizontalreuse#conflict_resolution

We abandoned the idea of an explicit exclude operator long ago. (I think =
it was never in the PHP SVN.)
Thus, the situation you describe cannot occur in the sense that a method =
is missing from the class.
However, you can of course provide incompatible method implementations. =
(Which does not make traits any different from any other way to =
implement an interface.)=20

Best regards
Stefan


--=20
Stefan Marr
Software Languages Lab
Vrije Universiteit Brussel
Pleinlaan 2 / B-1050 Brussels / Belgium
http://soft.vub.ac.be/~smarr
Phone: +32 2 629 2974
Fax:   +32 2 629 3525