constexpr cstr mockup

cstr.h

constexpr const char* end_of(const char* s) {
    while (*s != 0) ++s;
    return s;
}

struct cstr {
    const char* b_;
    const char* e_;

    constexpr cstr(const char* s)
    : b_(s)
    , e_(end_of(s))
    {}

    operator std::string () const {
        return std::string{b_, e_};
    }
};