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Date: Mon, 17 Oct 2011 20:19:09 +0200
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To: Stefan Marr <php@stefan-marr.de>
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Subject: Re: typehinting traits
From: tyra3l@gmail.com (Ferenc Kovacs)

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On Mon, Oct 17, 2011 at 8:00 PM, Stefan Marr <php@stefan-marr.de> wrote:

> Hi Ferenc:
>
> On 17 Oct 2011, at 19:41, Ferenc Kovacs wrote:
>
> > Hi Stefan,
> >
> > Multiple people asked me that how they can expect/check that a given
> object uses a trait or not.
> > Of course one could write the concrete methods as a trait and always us=
e
> a given interface for typehints, but I can't see why shouldn't instanceof
> and typehints in general work for traits.
> > Is the any technical or maybe theoretical argument against this?
>
> Originally I proposed traits including the semantics that traits directly
> implement interfaces.
>
> The discussion is somewhere here:
> http://www.mail-archive.com/internals@lists.php.net/msg33935.html
>
> I think Sebastian was the person with the strongest opinion on that
> particular issue:
>   http://www.mail-archive.com/internals@lists.php.net/msg33948.html
>
> And I tend to agree with him.
>
> Currently I think along the following lines:
>
>  A trait is not a full unit of reuse!
>  A class is.
>  Don't use traits where you should use classes and composition.
>  Traits do not guarantee anything, if you want to be sure your invariants
> hold, use classes and composition.
>
>  Traits allow to reuse behavior in a much more flexible way, but they do
> not replace classes.
>
> And, well, then there is this:
> https://wiki.php.net/rfc/horizontalreuse#requiring_composing_class_to_imp=
lement_interface
>
> That should make sure that people can use interfaces for the purpose
> envisioned here.
>
> For reference, there is also: https://bugs.php.net/bug.php?id=3D55613
>
>
> But aside of the things I said before:
>  - theoretically: keeping interfaces and traits apart is a good, clean
> language design decision.
>  - practically: people LOVE ugly languages, because they get things done
>
> So, well, I can't claim anything about value here.
> The current situation might be more friendly to the teacher.
> Another design might offer more freedom/power...


Thanks for the clarification.
Without either having the ability to check a trait or implement an interfac=
e
for a trait, or at least implementing the require syntax, I think that it
isn't really a non-fragile solution for my question.
AFAIK the only solution available currently is something like:

<?php
interface testTraitInterface{

}

trait testTrait{

}

class testClass implements testTraitInterface{
use testTrait;
}

$tc =3D new testClass;
var_dump($tc instanceof testTraitInterface);


Which is pretty weak of a solution, however if we only thinks traits as a
macro, this is enough, but then why bother with the as and insteadof, trait=
s
composed traits and such?
I think we will have much more feedback with the release of 5.4, so maybe w=
e
can re-consider extending the implementation for the next version.
And I agree that it is the best to only release what we are confident in,
and I'm happy that we waited a version for correctly implementing Closures
for objects.

Thanks again for the clarification and for your work on traits!

--=20
Ferenc Kov=C3=A1cs
@Tyr43l - http://tyrael.hu

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