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#include <iostream>
#include <cstddef>
 
template <char...>
struct string
{
	static const char c_str[];
};
 
template <char... S>
const char string<S...>::c_str[] = { S..., 0 };
 
template <typename T>
struct valdef
{
	typedef T value;
};
 
template <std::size_t...>
struct indices
{};
 
template <std::size_t, typename>
struct push_back;
 
template <std::size_t I, std::size_t... II>
struct push_back<I, indices<II...>>
	: valdef<indices<II..., I>>
{};
 
template <std::size_t N>
struct make_indices_impl
	: valdef
	<
		typename push_back
		<
			N,
			typename make_indices_impl<N - 1>::value
		>::value
	>
{};
 
template <>
struct make_indices_impl<0>
	: valdef<indices<0>>
{};
 
template <std::size_t N>
struct make_indices
	: valdef<typename make_indices_impl<N - 1>::value>
{};
 
template <>
struct make_indices<0>
	: valdef<indices<>>
{};
 
template <char const*, typename>
struct to_meta_string_impl;
 
template <char const* S, std::size_t... I>
struct to_meta_string_impl<S, indices<I...>>
	: valdef<string<S[I]...>>
{};
 
template <char const* S, std::size_t N>
struct to_meta_string
	: valdef
	<
		typename to_meta_string_impl
		<
			S,
			typename make_indices<N>::value
		>::value
	>
{};
 
struct static_string
{
	static constexpr char value[];
};
 
constexpr char static_string::value[] = "abcdef";
 
int main()
{
	std::cout << to_meta_string<static_string::value, 6>::value::c_str;
}

prog.cpp:63:18: error: template parameter 'S' of type 'const char*' is not allowed in an integral constant expression because it is not of integral or enumeration type
prog.cpp:63:21: error: an array reference cannot appear in a constant-expression
prog.cpp:63:22: error: expected parameter pack before '...'
prog.cpp:63:25: error: template argument 1 is invalid
prog.cpp: In instantiation of 'to_meta_string<((const char*)(& static_string::value)), 6u>':
prog.cpp:87:54:   instantiated from here
prog.cpp:76:1: error: no type named 'value' in 'struct to_meta_string_impl<((const char*)(& static_string::value)), indices<0u, 1u, 2u, 3u, 4u, 5u> >'
prog.cpp: In function 'int main()':
prog.cpp:87:56: error: 'to_meta_string<(const char*)&static_string::value, 6u>::value' has not been declared

Standard output is empty