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Date: Tue, 10 Feb 2015 07:40:18 +0000
Message-ID: <CAL=_i_=gg+WWU+d1K-A=rdf+f2=+mBGDVC4UKqmBOsiNMMBj1g@mail.gmail.com>
To: Yasuo Ohgaki <yohgaki@ohgaki.net>
Cc: Dmitry Stogov <dmitry@zend.com>, Patrick Schaaf <php@bof.de>, internals <internals@lists.php.net>
Content-Type: multipart/alternative; boundary=047d7b10cc359b4dd9050eb6ffe0
Subject: Re: [PHP-DEV] Design by Contract
From: pthreads@pthreads.org (Joe Watkins)

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Content-Type: text/plain; charset=UTF-8

Example code never works, I can just say that's a bad abstraction,
vertebrate and invertebrate are distinct and abstraction should reflect
that.

Why should we provide a way to change contracts is the question ?

It doesn't seem to make sense to do that, a derived class should be able to
define additional contracts, but not change the contracts of it's parent.

Cheers
Joe

On Tue, Feb 10, 2015 at 7:36 AM, Yasuo Ohgaki <yohgaki@ohgaki.net> wrote:

> Hi Joe,
>
> On Tue, Feb 10, 2015 at 4:31 PM, Joe Watkins <pthreads@pthreads.org>
> wrote:
>
>> Actually I'm not sure it's at all sane to try to override contracts, I'd
>> actually avoid that completely, so no need to name contracts and no need
>> for magic __invariant.
>
>
> For example,
>
> class Animal {
>    protected $legs;
>    require($legs >= 0);
> }
>
> class Snake extends Animal {
>   // Snake is fine, no leg
> }
>
> class Human extends Animal {
>   // 2 legs. $this->leg === 2
> }
>
> Overriding makes sense for many cases.
>
> Regards,
>
> --
> Yasuo Ohgaki
> yohgaki@ohgaki.net
>

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