Print arguments with indices (custom lower bound).

indexed_print_seq.cpp

#include <iostream>

// Integer sequence adapted from http://stackoverflow.com/a/17426611/2128694
// Just added the lower bound Lo.

template<class T> using Invoke = typename T::type;

template<unsigned...> struct seq{ using type = seq; };

template<class S1, class S2> struct concat;

template<unsigned... I1, unsigned... I2>
struct concat<seq<I1...>, seq<I2...>>
  : seq<I1..., (sizeof...(I1)+I2)...>{};

template<class S1, class S2>
using Concat = Invoke<concat<S1, S2>>;

template<unsigned N, unsigned Lo> struct gen_seq;
template<unsigned N, unsigned Lo = 0> using GenSeq = Invoke<gen_seq<N, Lo>>;

template<unsigned N, unsigned Lo>
struct gen_seq : Concat<GenSeq<N/2, Lo>, GenSeq<N - N/2, Lo>>{};

template<unsigned Lo> struct gen_seq<0, Lo> : seq<>{
    static_assert(Lo <= 0, "gen_seq: illegal 0 reach");
};
template<unsigned Lo> struct gen_seq<1, Lo> : seq<Lo>{};

struct VariadicPass {
    template <typename... Ts>
    VariadicPass(Ts&&...) {}
};

template <unsigned... Is, typename... Ts>
void print_impl(seq<Is...>, Ts&&... args)
{
    // Note: Should be evaluated left to right but isn't on
    // MSVC (at least until 12/2013) and gcc < 4.9.1.
    // http://connect.microsoft.com/VisualStudio/feedbackdetail/view/976911
    // http://gcc.gnu.org/bugzilla/show_bug.cgi?id=51253
    VariadicPass {(std::cout << Is << ':' << args << ';')...};
}

template <typename... Ts>
void indexed_print(Ts&&... args)
{
    print_impl(GenSeq<sizeof...(Ts), 5>(), std::forward<Ts>(args)...);
}

int main()
{
    indexed_print(42, "abc");
}