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Date: Wed, 29 Jan 2014 13:18:05 +0900
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To: Sebastian Krebs <krebs.seb@gmail.com>
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Subject: Re: [PHP-DEV] DbC for PHP?
From: yohgaki@ohgaki.net (Yasuo Ohgaki)

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Hi Sebastian,

On Tue, Jan 28, 2014 at 5:36 PM, Sebastian Krebs <krebs.seb@gmail.com>wrote:

> I'm wandering if we could have DbC (Design by Contract) for PHP 6.
>> http://en.wikipedia.org/wiki/Design_by_contract
>>
>> There is user land implementation already.
>>
>> https://gitorious.org/higher-order-php/php-contracts/source/5b0a53b9732f0e4dbe79345212c84c74526def3b
>> :
>>
>> It could be done with dbc mode INI switch as follows.
>>
>> When dbc=on, automatically includes
>>
>> include __dbc_ . __SCRIPT_NAME__;
>>
>>  when a script is loaded. No error if there is not the script.
>> When function/method is called
>>
>> __dbc_pre_. __FUNCTION__() is called before calling function().
>> __dbc_post_.___FUNCTION__() is called after function() call.
>>
>> No error if there is not the function.
>>
>
> Couldn't you achieve the same with assert()?
>

Assert can be used for DbC and there are such implementations.

Precondition is easy with assert(), but post condition is rather difficult
since
we need assert() before every 'return'. This could damage production code
(code executed on production environment) and contract readability. It
increases
chances of omitting post condition check by mistake.

Similar mistake may happen with this.
We may better to have option to warn non existent pre/post check.


Like Alexander explained, pure OO code can use DbC. It may be enough
for people who are interested in DbC.

This is just an idea. It's simple, powerful and easy to adopt. Since there
is no DbC code in production code, it's fast while assert() need
compilation
overhead. It does not matter much with opcache, though.

With this approach, user has to look up contract in other file. This is
disadvantage over other methods.

I wander how many of us are interested in such feature.

Regards,

--
Yasuo Ohgaki
yohgaki@ohgaki.net

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