On 09/11/2012 08:45 p.m., Lorenzo Caminiti wrote:

Is there a way to inspect if a type is a template instantiaton (is_templated) and the type of the instantiated template parameters (arg1_type)?

is_templated< std::vector<int> >::value // true is_templated< int >::value // false

template_traits< std::vector<int> >::arg1_type // int

I uploaded template traits to the vault a long time ago. You can find it at https://github.com/boost-vault/Miscellaneous as template_traits.zip, or simply https://github.com/boost-vault/Miscellaneous/blob/master/template_traits.zip It works only for templates of type arguments, no non-type or template arguments. There were other limitations, but I no longer remember them. Agustín K-ballo Bergé.- http://fusionfenix.com

Le 10/11/12 00:45, Lorenzo Caminiti a écrit :

Hi,

Is there a way to inspect if a type is a template instantiaton (is_templated) and the type of the instantiated template parameters (arg1_type)?

is_templated< std::vector<int> >::value // true is_templated< int >::value // false

template_traits< std::vector<int> >::arg1_type // int

Hi Lorenzo, The following works for c++98 and C++11. I left you rework the C++98 part to make it variadic with the help of the preprocessor ;-) Just before sending I saw that others were quicker than me :( Hoping this helps, Vicente #include <boost/type_traits.hpp> #if defined(BOOST_NO_CXX11_VARIADIC_TEMPLATES) template <typename T> struct is_templated : boost::false_type{}; template <template <class> class T, typename Arg1> struct is_templated<T<Arg1> > : boost::true_type {}; template <template <class, class> class T, typename Arg1, typename Arg2> struct is_templated<T<Arg1,Arg2> > : boost::true_type{}; // ... preprocessor template <typename T, std::size_t N> struct template_arg {}; template <template <class> class T, typename Arg1> struct template_arg<T<Arg1>,1> : boost::mpl::identity<Arg1>{}; template <template <class,class> class T, typename Arg1, typename Arg2> struct template_arg<T<Arg1,Arg2>,1> : boost::mpl::identity<Arg1>{}; template <template <class,class> class T, typename Arg1, typename Arg2> struct template_arg<T<Arg1,Arg2>,2> : boost::mpl::identity<Arg2>{}; // ... preprocessor #else template <typename T> struct is_templated : boost::false_type{}; template <template <class...> class T, typename ...Args> struct is_templated<T<Args...>> : boost::true_type {}; template <std::size_t N, typename ...Args> struct nth; template <typename Arg, typename ...Args> struct nth<1, Arg, Args...> : boost::mpl::identity<Arg> {}; template <std::size_t N, typename Arg, typename ...Args> struct nth<N, Arg, Args...> : nth< N-1, Args...> {}; template <typename T, std::size_t N> struct template_arg {}; template <std::size_t N, template <class...> class T, typename ...Args> struct template_arg<T<Args...>, N>: nth<N, Args...>{}; #endif // TEST #include <vector> #include <boost/static_assert.hpp> BOOST_STATIC_ASSERT((is_templated<std::vector<int> >::value )); BOOST_STATIC_ASSERT((is_templated<int>::value == false )); BOOST_STATIC_ASSERT((boost::is_same<template_arg<std::vector<int>, 1>::type, int>::value));