Ticket #6815: templ_literal.h

#ifndef TEMPL_LITERAL_H
#define TEMPL_LITERAL_H

#include <cstddef>
#include <boost/preprocessor.hpp>

#ifndef TEMPLATE_LITERAL_MAX_SYM
#define TEMPLATE_LITERAL_MAX_SYM 20
#endif

template< char... >
struct TemplateLiteral { };

template< std::size_t LEN, char CHAR, char... CHARS >
struct TemplateLiteralTrim
{
private:
        template< bool, class, char... >
        struct Helper;
        template< char... C1, char... C2 >
        struct Helper< false, TemplateLiteral<C1...>, C2... >
        {
                static_assert(sizeof...(C1) == LEN, "Literal is too large. Extend it with #define TEMPLATE_LITERAL_MAX_SYM");
                typedef TemplateLiteral<C1...> Result;
        };
        template< char... C1, char c1, char c2, char... C2 >
        struct Helper< true, TemplateLiteral<C1...>, c1, c2, C2... >
        {
                typedef typename Helper< (bool)c2, TemplateLiteral<C1..., c1>, c2, C2...>::Result Result;
        };
public:
        typedef typename Helper<(bool)CHAR, TemplateLiteral<>, CHAR, CHARS..., '\0' >::Result Result;
};

template< class T, std::size_t N >
constexpr inline std::size_t sizeof_literal( const T (&)[N] )
{
        return N;
}

template< std::size_t M >
constexpr inline char getNthCharSpec( std::size_t N, const char (&literal)[M] )
{
        return N < M ? literal[N] : '\0';
}

#define GET_Nth_CHAR_FOR_PP(I, N, LIT) ,getNthCharSpec(N, LIT)

#define TEMPLATE_LITERAL_BASE(MAX, LIT) \
        (typename TemplateLiteralTrim< sizeof_literal(LIT) - 1 \
        BOOST_PP_REPEAT(MAX, GET_Nth_CHAR_FOR_PP, LIT) >::Result())

#define TEMPLATE_LITERAL(LITERAL) TEMPLATE_LITERAL_BASE(TEMPLATE_LITERAL_MAX_SYM, LITERAL)

#endif //TEMPL_LITERAL_H