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

Subject: Re: [boost] [contract] assertion requirements as meta-functions or not?
From: Vicente J. Botet Escriba (vicente.botet_at_[hidden])
Date: 2012-04-24 12:28:19

Le 24/04/12 14:31, lcaminiti a écrit :
> 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
>
Hi,

I don't know if following the the _c suffix rule in Boost could help.

             x<  y ? result == x : result == y,
                     requires boost::has_equal_to<T>  // meta-function

and

             x<  y ? result == x : result == y,
                     requires*_c*  boost::has_equal_to<T>::value // value

Best,
Vicente