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.