Re: [boost] [contract] assertion requirements as meta-functions or not?

Subject: Re: [boost] [contract] assertion requirements as meta-functions or not?
From: Andrzej Krzemienski (akrzemi1_at_[hidden])
Date: 2012-04-24 09:19:17

Hi Lorenzo,
If I understand your question and Boost.Contract design correctly, it looks
like the former approach is more flexible in cases where I do _not_ want to
use a meta-function to describe a constraint:

  postcondition(
    auto result = return,
    some_cond1(result), requires x / 2 == 0,
    some_cond2(result), requires noexcept(x),
    some_cond3(result), requires sizeof(x) > 2,
  )

Although I am not sure if such constraints would be useful in real life.
Regards,
&rzej.

2012/4/24 lcaminiti <lorcaminiti_at_[hidden]>

> Hello all,
>
> Boost.Contract allows to specify "assertion requirements":
>
>    /assertion-condition/, requires /assertion-requirement/
>
> If the requirement is not met then the assertion condition is neither
> compiled nor checked at run-time.
>
> Question: Shall the assertion-requirement be a nullary boolean
> meta-function
> or just a static boolean value?
>
> For example:
>
> CONTRACT_FUNCTION(
>    template( typename T ) requires( boost::LessThanComparable<T> )
>    (T const&) (min) ( (T const&) x, (T const&) y )
>        postcondition(
>            auto result = return,
>            x < y ? result == x : result == y,
>                    requires boost::has_equal_to<T>::value // static boolean
>        )
> ) {
>    return x < y ? x : y; // OK: T is less than comparable `<`.
> }
>
> For now, the assertion requirement is a static boolean value so it can be
> more easily manipulated (using !, &&, ||, etc instead of mpl::not,
> mpl::and,
> mpl::or, etc). However, is there any strong reason for marking the
> assertion
> requirement a nullary boolean meta-function instead like the following
> code?
>
>            x < y ? result == x : result == y,
>                    requires boost::has_equal_to<T> // meta-function
>
> Thanks.
> --Lorenzo
>
>
> --
> View this message in context:
> http://boost.2283326.n4.nabble.com/boost-contract-assertion-requirements-as-meta-functions-or-not-tp4583283p4583283.html
> Sent from the Boost - Dev mailing list archive at Nabble.com.
>
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