concatenate

#include <iostream>
#include <typeinfo>

#include <cstdlib>
#include <cassert>

#include <cxxabi.h>

template< typename ...types >
struct V // implementation
{

    using type = V;

};

template< typename ...first, typename ...second, typename ...rest >
struct V< V< first... >, V< second... >, rest... >
    : V< V< first..., second... >, rest... >
{

};

template< typename first, typename ...second, typename ...rest >
struct V< first, V< second... >, rest... >
    : V< V< first, second... >, rest... >
{

};

template< typename ...first, typename second, typename ...rest >
struct V< V< first... >, second, rest... >
    : V< V< first..., second >, rest... >
{

};

template< typename ...types >
struct V< V< types... > >
    : V< types... >
{

};

template< int i >
struct T
{

};

int
main()
{
    auto name = typeid(typename V< T< 0 >, V< T< 1 >, T< 2 > >, T< 3 >, T< 4 >, V< T< 5 >, T< 6 > >, V< T< 7 >, T< 8 > >, T< 9 > >::type).name();
    int status = -4;
    char * demangled_name = abi::__cxa_demangle(name, nullptr, nullptr, &status);
    assert(!(status < 0));
    std::cout << demangled_name << std::endl;
    std::free(demangled_name);
    return EXIT_SUCCESS;
}