Patch for std::get<>() problem with Windows LLVM clang

[lovemycatt]

These patches are required in order to build on Windows with LLVM clang 5.0 toolset (either with mingw or with MSVC using LLVM-vs2014 toolset).

Basically, the encountered problem is that, under certain (many) conditions, std::get<>() is not able to cast a named_tuple<> or a tagged_tuple<> to its base std::tuple<>.
This is the case, for instance, of the named_tuple::operator[].

I believe this is a bug of the Windows version of LLVM clang distribution, anyways the patched code introduces no overhead and is quite simple.

The proposed solution implements to patches:

• an explicitly cast to the base std::tuple<> in std::get<>() calls in tagged.hpp (a simple solution, yet nor general as other client code may use std::get<>() on a tagged_tuple<>);
• ovverridden std::get<>() functions for named_tuple<> in named_tuple.hpp (a bit longer solution, but more general, also fixes al client code that uses std::get<>() on named_tuple<> and, as far as I have seen, on any other derived classes).

I'd be curious to know your opinion on this strange LLVM 'bug', and if you can imagine better solutions (other than working on Linux :)).

Follows a sample error log:

  In file included from D:\Users\Tulmenga\Projects\prj_0lf\factory_0lf\0lf\0lf/internal/logger_def_dumpers.hh:23:
1>D:\Users\Tulmenga\Projects\prj_0lf\factory_0lf\0lf\..\named_types\includes\named_types/named_tuple.hpp(170,12): error : no matching function for call to 'get'
1>      return std::get<
1>             ^~~~~~~~~
1>  D:\Users\Tulmenga\Projects\prj_0lf\factory_0lf\0lf\src\process_monitor.cpp(132,23):  note: in instantiation of function template specialization 'named_types::named_tuple<unsigned long long (named_types::named_tag<named_types::string_literal<char, 'a', 'c', 't', 'o', 'r', 's'> >), double (named_types::named_tag<named_types::string_literal<char, 'm', 'o', 'd', '_', 'c', 'p', 'u'> >), double (named_types::named_tag<named_types::string_literal<char, 's', 'y', 's', '_', 'c', 'p', 'u'> >), unsigned long long (named_types::named_tag<named_types::string_literal<char, 'm', 'o', 'd', '_', 'r', 'a', 'm'> >), std::basic_string<char, std::char_traits<char>, std::allocator<char> > (named_types::named_tag<named_types::string_literal<char, 't', 'r', 'a', 'c', 'e', '_', 'm', 'o', 'd', 'e'> >), unsigned long long (named_types::named_tag<named_types::string_literal<char, 's', 'y', 's', '_', 'f', 'r', 'e', 'e', '_', 'r', 'a', 'm'> >)>::operator[]<named_types::string_literal<char, 'a', 'c', 't', 'o', 'r', 's'> >' requested here
1>                  info_ [_(actors)] = home_system().registry().running();
1>                        ^
1>  C:\apps\MSStudio2015\VC\include\utility(518,3):  note: candidate template ignored: could not match 'pair' against 'named_tuple'
1>                  get(pair<_Ty1, _Ty2>& _Pr) _NOEXCEPT
1>                  ^
1>  C:\apps\MSStudio2015\VC\include\utility(542,3):  note: candidate template ignored: could not match 'pair' against 'named_tuple'
1>                  get(const pair<_Ty1, _Ty2>& _Pr) _NOEXCEPT
1>                  ^
1>  C:\apps\MSStudio2015\VC\include\utility(567,3):  note: candidate template ignored: could not match 'pair' against 'named_tuple'
1>                  get(pair<_Ty1, _Ty2>&& _Pr) _NOEXCEPT
1>                  ^
1>  C:\apps\MSStudio2015\VC\include\tuple(882,3):  note: candidate template ignored: failed template argument deduction
1>                  get(tuple<_Types...>& _Tuple) _NOEXCEPT
1>                  ^
1>  C:\apps\MSStudio2015\VC\include\tuple(892,3):  note: candidate template ignored: failed template argument deduction
1>                  get(const tuple<_Types...>& _Tuple) _NOEXCEPT
1>                  ^
1>  C:\apps\MSStudio2015\VC\include\tuple(902,3):  note: candidate template ignored: failed template argument deduction
1>                  get(tuple<_Types...>&& _Tuple) _NOEXCEPT
1>                  ^
1>  C:\apps\MSStudio2015\VC\include\array(493,17):  note: candidate template ignored: could not match 'array' against 'named_tuple'
1>          constexpr _Ty& get(array<_Ty, _Size>& _Arr) _NOEXCEPT
1>                         ^
1>  C:\apps\MSStudio2015\VC\include\array(502,23):  note: candidate template ignored: could not match 'array' against 'named_tuple'
1>          constexpr const _Ty& get(const array<_Ty, _Size>& _Arr) _NOEXCEPT
1>                               ^
1>  C:\apps\MSStudio2015\VC\include\array(511,18):  note: candidate template ignored: could not match 'array' against 'named_tuple'
1>          constexpr _Ty&& get(array<_Ty, _Size>&& _Arr) _NOEXCEPT
1>                          ^
1>  C:\apps\MSStudio2015\VC\include\utility(526,18):  note: candidate template ignored: invalid explicitly-specified argument for template parameter '_Ty1'
1>          constexpr _Ty1& get(pair<_Ty1, _Ty2>& _Pr) _NOEXCEPT
1>                          ^
1>  C:\apps\MSStudio2015\VC\include\utility(533,18):  note: candidate template ignored: invalid explicitly-specified argument for template parameter '_Ty2'
1>          constexpr _Ty2& get(pair<_Ty1, _Ty2>& _Pr) _NOEXCEPT
1>                          ^
1>  C:\apps\MSStudio2015\VC\include\utility(551,24):  note: candidate template ignored: invalid explicitly-specified argument for template parameter '_Ty1'
1>          constexpr const _Ty1& get(const pair<_Ty1, _Ty2>& _Pr) _NOEXCEPT
1>                                ^
1>  C:\apps\MSStudio2015\VC\include\utility(558,24):  note: candidate template ignored: invalid explicitly-specified argument for template parameter '_Ty2'
1>          constexpr const _Ty2& get(const pair<_Ty1, _Ty2>& _Pr) _NOEXCEPT
1>                                ^
1>  C:\apps\MSStudio2015\VC\include\utility(575,19):  note: candidate template ignored: invalid explicitly-specified argument for template parameter '_Ty1'
1>          constexpr _Ty1&& get(pair<_Ty1, _Ty2>&& _Pr) _NOEXCEPT
1>                           ^
1>  C:\apps\MSStudio2015\VC\include\utility(582,19):  note: candidate template ignored: invalid explicitly-specified argument for template parameter '_Ty2'
1>          constexpr _Ty2&& get(pair<_Ty1, _Ty2>&& _Pr) _NOEXCEPT
1>                           ^
1>  C:\apps\MSStudio2015\VC\include\tuple(914,17):  note: candidate template ignored: invalid explicitly-specified argument for template parameter '_Ty'
1>          constexpr _Ty& get(tuple<_Types...>& _Tuple) _NOEXCEPT
1>                         ^
1>  C:\apps\MSStudio2015\VC\include\tuple(922,23):  note: candidate template ignored: invalid explicitly-specified argument for template parameter '_Ty'
1>          constexpr const _Ty& get(const tuple<_Types...>& _Tuple) _NOEXCEPT
1>                               ^
1>  C:\apps\MSStudio2015\VC\include\tuple(930,18):  note: candidate template ignored: invalid explicitly-specified argument for template parameter '_Ty'
1>          constexpr _Ty&& get(tuple<_Types...>&& _Tuple) _NOEXCEPT
1>                          ^
1>  D:\Users\Tulmenga\Projects\prj_0lf\factory_0lf\0lf\..\named_types\includes\std/experimental/tagged.hpp(233,1):  note: candidate template ignored: invalid explicitly-specified argument for template parameter 'Tag'
1>  get(tagged_tuple<Types...> const& input) {
1>  ^
1>  D:\Users\Tulmenga\Projects\prj_0lf\factory_0lf\0lf\..\named_types\includes\std/experimental/tagged.hpp(239,1):  note: candidate template ignored: invalid explicitly-specified argument for template parameter 'Tag'
1>  get(tagged_tuple<Types...>& input) {
1>  ^
1>  D:\Users\Tulmenga\Projects\prj_0lf\factory_0lf\0lf\..\named_types\includes\std/experimental/tagged.hpp(245,1):  note: candidate template ignored: invalid explicitly-specified argument for template parameter 'Tag'
1>  get(tagged_tuple<Types...>&& input) {
1>  ^

[duckie]

Thank you very much for this contribution. I need to review since it breaks some compilations on XCode : https://travis-ci.org/duckie/named_types/builds/229891574

I am surprised the Travis result doesnt show here.

[lovemycatt]

Thanks for taking it into consideration.
If you need some further tests on Windows (VS2015, v140_clang_c2, LLVM, Mingw), just tell me.

[duckie]

@lovemycatt I fixed a discrepancy in the code that fixes the Linux build and should still work with MSVC. Can you try it ? You gotta pull my feature branch into yours (same name)