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Date: Mon, 16 Feb 2015 14:56:07 +0900
Message-ID: <CAGa2bXZXm3zq_OTtZ7WvUm_bsoiR_Hm2bybmH8y0uAeVtt12Dw@mail.gmail.com>
To: francois <francois@php.net>
Cc: Dmitry Stogov <dmitry@zend.com>, Joe Watkins <pthreads@pthreads.org>, 
	Stanislav Malyshev <smalyshev@gmail.com>, PHP Internals <internals@lists.php.net>
Content-Type: multipart/alternative; boundary=001a114284d66ca984050f2e403a
Subject: Re: [PHP-DEV] Design by Contract
From: yohgaki@ohgaki.net (Yasuo Ohgaki)

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Hi Francois,

On Mon, Feb 16, 2015 at 8:08 AM, Fran=C3=A7ois Laupretre <francois@php.net>
wrote:
>
> > De : yohgaki@gmail.com [mailto:yohgaki@gmail.com] De la part de Yasuo
Ohgaki
> >
> > D resolves that if parameter is contract or not at compile time and
checks it if method
> > is overriding parent's method. If method is overridden, D just ignores
contract.
>
> That's true for pre-conditions, but that's not the way D handles
post-conditions.
>
> >>> The same rule for class applies to interfaces.
> >>
> >> ?? I don't understand.
> >
> >Interface may have contracts just like class.
>
> OK, but when do you check interface conditions ? And how do you deal with
interface (multiple) inheritance ?

Simply check all contracts on method calls.
If property check (invariant) could be issue, class designer should use
document for proper
property management rather than contracts. Or we may drop invariant support
for interface.

>
> >>> We cannot ignore parent class invariants. If developer violate parent
> >>> property restrictions,
> >>> it's violation of parent class type and this must be forbidden. It's
> >>> checked by invariant contract.
> >>
> >> I agree.
> >
> > We have(had) weak type system. Choosing right type system for PHP would
be very hard.
> > I didn't intended to bring this topic... Could we introduce simple
"Design by Contract"
> > concept?  Or are we going to discuss right type system for PHP?
>
> Sure, but are you realizing that you're discarding your own statement,
not mine ?

Type safety consideration was not intended at first.
So I don't have problem with disregarding type safety.
We may introduce type safety/system when we have template, strict types
and/or overloading, for example.

> I never told about the PHP type system because I don't understand what
types have to do here. So, yes, I don't care about the PHP type system and
that's not the subject. We are discussing about PHP conditions and when
they are evaluated, that's all.
>
> And, sorry about that, but could you stop sending html messages ? It
makes replies much harder.

It seems gmail does not have the option, but I can only remove text
formatting manually.
Does this mail seems OK to you?

Anyway, how about not to consider type safety too much now? and
concentrate to introduce simple DbC?
We may have option for strict type in the future for whatever type system
we introduce at that time.

Regards,

--
Yasuo Ohgaki
yohgaki@ohgaki.net

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