Re: [boost] [contract] static if instead of assertion requirements

Subject: Re: [boost] [contract] static if instead of assertion requirements
From: Lorenzo Caminiti (lorcaminiti_at_[hidden])
Date: 2012-10-03 02:15:34

On Tue, Oct 2, 2012 at 9:10 PM, Mathias Gaunard
<mathias.gaunard_at_[hidden]> wrote:
> On 10/02/2012 11:32 PM, Lorenzo Caminiti wrote:
>>
>> Hello all,
>>
>> I was reading the proposal to add "static if" to C++1x and I will use
>> such a syntax for assertion requirements:
>> http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2012/n3329.pdf
>>
>> Current syntax for assertion requirements:
>>
>>      postcondition(
>>          back() == value, requires boost::has_equal<T>::value
>>      )
>>
>> Will be replaced with static if:
>>
>>      postcondition(
>>          static if(boost::has_equal<T>::value) (
>>              back() == value
>>          ) // optional else ( ... )
>>      )
>>
>> If there were interested, I could even provide a separate
>> BOOST_STATIC_IF(const_condition, then_code, else_code)... however,
>> such a macro could only be used at namespace and class scope, not a
>> function scope :(
>
>
> Huh? How does that work?
>
> The only way to implement static if that I know of only works at function
> scope.

Yeah, can't do BOOST_STATIC_IF... sorry, I spoke to soon...

(I can still do static if in pre/post/inv because that's for
expressions within Boost.Contract syntax and extra function templates
are declared to wrap the expression but disabled if the static if
condition is false. That works same as Boost.Contract current
assertion requirements only using the "static if(const_bool) ( ... )
[else (...)]" syntax instead of "bool, requires const_bool".)

--Lorenzo