[boost] Re: compressed_pair requirements?

From: David Abrahams (dave_at_[hidden])
Date: 2005-06-06 10:11:40

"Eric Niebler" <eric_at_[hidden]> writes:

> Howard Hinnant wrote:
>> The scary part is that we do so many useful things these days by
>> tentatively passing non-POD's past an ellipses, though only at
>> compile time, never at run time.  But the compiler is not making
>> that distinction.
>> This is a big problem, and I suspect it will need to be addressed at
>> the standards level.  I don't have a solution yet.
>> 
>
>
> The solution is to not pass non-PODs through ellipses, of course. ;-)
>
>   double is_mem_fun_ptr_tester(...);
>
>   template<typename Class, typename Ret>
>   char is_mem_fun_ptr_tester(Ret (Class::**)());
>
>   template<typename T>
>   struct is_member_function_pointer
>   {
>     BOOST_STATIC_CONSTANT(bool,
>       value = 1==sizeof(is_mem_fun_ptr_tester(static_cast<T*>(0))));
>   };
>
>   typedef char test1[
>     is_member_function_pointer<void (dummy::*)()>::value ];
>   typedef char test2[
>     !is_member_function_pointer<dummy>::value ];

You have to take some steps to eliminate the formation of
pointers-to-references, i.e. a partial specialization on compilers
that support it and some wretched mess everywhere else.

-- 
Dave Abrahams
Boost Consulting
www.boost-consulting.com