If http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2012/n3402.pdf is the final version accepted for C++14, the standard will use, e.g.
namespace std { namespace suffixes { namespace chrono {
One of the advantages is that we can add some utilities. I helped Peter Sommerlad to port his reference implementation to Boost (See https://github.com/PeterSommerlad/UDLSuffixBoost/tree/master/boost/suffixes). There are some interesting utilities that make easier implementing suffixes. I guess it would like to name his library Boost.Suffixes. This doesn't means that we can not choose your option.
I hadn't seen that before, thanks for the heads up. If we have UDL utilities in boost then I agree they should have their own top-level namespace in Boost, whether it makes sense to group all literals in there is another matter. My gut feeling is that users will find boost::mylib::literals or boost::mylib::suffixes easier, but I can see how it would make sense for the std to go your way. BTW, I believe your implementation of parse_int is unnessarily complex, looks like that whole file can be reduced to just: template <unsigned base, unsigned long long val, char... Digits> struct parse_int { // The default specialization is also the termination condition: // it gets invoked only when sizeof...Digits == 0. static_assert(base<=16u,"only support up to hexadecimal"); static constexpr unsigned long long value{ val }; }; template <unsigned base, unsigned long long val, char c, char... Digits> struct parse_int<base, val, c, Digits...> { static constexpr unsigned long long char_value = (c >= '0' && c <= '9') ? c - '0' : (c >= 'a' && c <= 'f') ? c - 'a' : (c >= 'A' && c <= 'F') ? c - 'A' : 400u; static_assert(char_value < base, "Encountered a digit out of range"); static constexpr unsigned long long value{ parse_int<base, val * base + char_value, Digits...>::value }; }; Typical usage is: template <char...PACK> constexpr unsigned long long operator "" _b() { return parse_int<2, 0, PACK...>::value; } constexpr unsigned bt = 1001_b; static_assert(bt == 9, ""); More than that though: I can't help but feel that base 8, 10 and 16 parsing is much better (faster) handled by the compiler, so parse_int could be reduced to base-2 parsing only which would simplify it still further. What's the rationale for the chrono integer literals parsing the ints themselves rather than using cooked literals? Cheers, John.