Re: [Boost-users] std::is_tr1_tuple<T> - how?

From: John Maddock (john_at_[hidden])
Date: 2008-08-25 05:26:39

Markus Werle wrote:
> While migrating from boost::tuple to std::tr1::tuple (pain!) I have to
> rewrite a lot of compile-time-magic code.
> Among other things I am in need of a type info
>
> template <typename T> struct is_tr1_tuple;
>
> Any implementation hint or proposal welcome.

This is tricky, when BOOST_HAS_TR1_TUPLE is *not* defined, then 
std::tr1::tuple is an alias for either boost::fusion::tuple or boost::tuple 
(the latter for broken Borland compilers only), so your existing metacode 
should work.

When BOOST_HAS_TR1_TUPLE *is* defined then std::tr1::tuple is the std lib's 
native implementation, you could probably use function overload resolution 
to detect that:

template <class T1, class T2 ... class T10>
char is_tr1_tuple_test(const std::tr1::tuple<T1....T10>&);

template <class T>
double is_tr1_tuple_test(const T&);

template <class T>
struct is_tr1_tuple
{
  static const T m_t;
  static const bool value = sizeof(is_tr1_tuple_test(m_t) == 1;
};

In fact I think that should work for the case that BOOST_HAS_TR1_TUPLE is 
not defined as well?

HTH, John.