Re: [Boost-users] puzzle with enable_if

Subject: Re: [Boost-users] puzzle with enable_if
From: Gevorg Voskanyan (v_gevorg_at_[hidden])
Date: 2010-04-15 09:03:45

Hi John,

John Dlugosz wrote:
> I'm using the Microsoft 2008 compiler.

> The template

> template <typename T, typename D>
> struct is_proper_TD_types : 
> std::tr1::integral_constant<bool,
    
> is_Universal_time_API<T>::value &&
      
> (std::tr1::is_same<typename T::duration_t,D>::value || 
    
>    std::tr1::is_same<duration,D>::value || 
      
> std::tr1::is_same<linear_duration,D>::value || 
      
> is_dimensional_time<D>::value)
> {};

> gives an error 
> "'T': must be a class or namespace when followed by '::'" when T is int.  

Move the integral constant type you are deriving from to the template parameter list for SFINAE to apply. In this case that'll be:

template <typename T, typename D,
               typename Enable = std::tr1::integral_constant<bool,                                              is_Universal_time_API<T>::value &&
                                              (std::tr1::is_same<typename T::duration_t,D>::value || 
                                              std::tr1::is_same<duration,D>::value || 
                                              std::tr1::is_same<linear_duration,D>::value || 
                                              is_dimensional_time<D>::value) > >
struct is_proper_TD_types : Enable {};

Please let me know if this works for you.

HTH,
Gevorg

P.S.

BTW, has my suggestion in the thread "Choosing a variable size" worked for you?