Handle std::string_view in top-level spreadsort

[Morwenn]

The top-level spreadsort function has specific overloads targeting std::string and std::wstring specifically. With C++17 around the corner, these overloads could also accept std::string_view and std::wstring_view when they are available.

It notably helps std::string_view to be more of a "drop-in replacement for std::string" as much as possible.

By the way, is string_spread_sort also intended to sort collections of std::vector<char> or std::deque<char>, or is it not suited for these cases?

[spreadsort]

string_sort is suitable for sorting std::vector and std::deque; you may need to write functors to support it though.

If I added support for string_views, is it feasible to do so cleanly without breaking older compilers?

I'm curious: though it's significantly faster at sorting strings, is anybody using this?

[Morwenn]

Couldn't you simply add the following to the top-level spreasort.h?

#ifdef __cpp_string_view
template <class RandomAccessIter>
inline typename boost::enable_if_c<
  is_same<typename std::iterator_traits<RandomAccessIter>::value_type,
          typename std::string_view>::value, void >::type
spreadsort(RandomAccessIter first, RandomAccessIter last)
{
  string_sort(first, last);
}

template <class RandomAccessIter>
inline typename boost::enable_if_c<
  is_same<typename std::iterator_traits<RandomAccessIter>::value_type,
          typename std::wstring_view>::value &&
  sizeof(wchar_t) == 2, void >::type
spreadsort(RandomAccessIter first, RandomAccessIter last)
{
  boost::uint16_t unused = 0;
  string_sort(first, last, unused);
}
#endif

I couln't find the exact feature test macro __cpp_string_view, but there ought to be an equivalent somewhere in Boost. It's just additional overloads with an SFINAE condition in the return type, so I don't think it would break anything. Alternatively, you could also alter the SFINAE conditions of the already existing functions, but I don't know whether it's ABI-breaking, and I don't know either whether Boost cares about breaking the ABI.

Regarding whether people do sort collections of std::string_view: I don't think many people already do that since it's fairly new, but I found a few occurrences of people doing that on GitHub.

[spreadsort]

That link doesn't work for me.

If you figure out an appropriate ifdef and a way to test it on a current version of gcc I can download, I'm happy to test and add it. Until then, unless there is significant demand, It'll wait.