Re: [boost] Workaround for compiler bugs

Subject: Re: [boost] Workaround for compiler bugs
From: Edward Diener (eldiener_at_[hidden])
Date: 2010-12-06 23:47:46

On 12/6/2010 7:43 PM, Stephan T. Lavavej wrote:
> [Edward Diener]
>> You missed the fact in the attachment that the T passed in must be the
>> full signature of a pointer to data member, as in 'Gipf Dvonn::*' in
>> your first example below.
>
> I wasn't sure if mentioning the data member's type was a desired feature of your code. Here's how to achieve that:
>
> C:\Temp>type meow.cpp
> #include<type_traits>
>
> #define DEFINE_HAS_MEMBER_OF_TYPE(NAME)                                     \
> template<typename T>  class has_member_ ## NAME {                           \
> private:                                                                    \
>      template<typename U>  static std::true_type helper(decltype(&U::NAME)); \
>      template<typename U>  static std::false_type helper(...);               \
> public:                                                                     \
>      typedef decltype(helper<T>(nullptr)) type;                              \
>      static const bool value = type::value;                                  \
> };                                                                          \
>                                                                              \
> template<typename T, typename X, bool B>                                    \
>      struct has_member_ ## NAME ## _of_type_helper                           \
>      : public std::false_type { };                                           \
>                                                                              \
> template<typename T, typename X>                                            \
>      struct has_member_ ## NAME ## _of_type_helper<T, X, true>                \
>      : public std::is_same<decltype(&T::NAME), X T::*>  { };                  \
>                                                                              \
> template<typename T, typename X>                                            \
>      struct has_member_ ## NAME ## _of_type                                  \
>      : public has_member_ ## NAME ## _of_type_helper<                         \
>          T, X, has_member_ ## NAME<T>::value>  { };

Thanks ! I will look at this and see what I can do with it, but I have 
to achieve this without the use of 'decltype'. The obvious reason is 
that 'decltype' is C++0x and I will almost certainly target my library 
for C++ compilers which support only C++03 instead at the base level of 
use. Obviously I do not mind using C++0x features as long as a compiler 
supports them but if they do not, this should still be workable without 
them. Also, while VC++ 10 supports decltype, VC++ 9 and below does not 
and I need to get my library working with those earlier versions of VC++ 
also.