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Fixups to type trait aliases

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* Apparently, even VS 2013 includes the general type alias templates. Allow their use there.
* Removed broken C++11 value alias templates (values aren't even allowed this fashion).
* VS 2015 Update 2 apparently both introduced support for variable templates and added them for type traits. Updated accordingly.
* Blocked off the entire variable template section until we bump out min compiler version, since there's no way to implement
  them without variable templates.
This commit is contained in:
Charles Dang 2017-05-16 02:02:53 +11:00
parent 723297efed
commit 01d59074eb
1 changed files with 14 additions and 18 deletions
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32
src/utils/type_trait_aliases.hpp
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@ -21,9 +21,10 @@ namespace utils
{
//
// These aliases are part of the standard starting with C++14.
// Forward to their declarations if appropriate.
// MSVC included them itself starting as of VS 2013 (our min supported version).
// Forward to their declarations as appropriate.
//
#ifdef HAVE_CXX14
#ifdef HAVE_CXX14 || defined(_MSC_VER)
using std::add_const_t;
using std::conditional_t;
@ -32,7 +33,7 @@ using std::remove_const_t;
using std::remove_reference_t;
using std::remove_pointer_t;
#else // We do not have C++14
#else // We do not have C++14 or MSVC
// add_const
template<typename T>
@ -60,18 +61,21 @@ using remove_pointer_t = typename std::remove_pointer<T>::type;
#endif // HAVE_CXX14
// Since there's really no way to implement these without variable templates, I've commented
// this whole section out until we bump our min compiler support to VS 2015 and GCC 5.
#if 0
//
// These aliases are part of the standard starting with C++17.
// However, they can also be implemented using variable templates in C++14. VS doesn't
// support variable templates until VS 2017, so fall back to the C++11 implementation
// if applicable.
// However, MSVC includes them as of VS 2015 Update 2, and they can also be implemented
// using variable templates in C++14.
//
#ifdef HAVE_CXX17
#ifdef HAVE_CXX17 || defined(_MSC_VER) && _MSC_VER >= 1900
using std::is_base_of_v;
using std::is_same_v;
#elif defined(HAVE_CXX14) || defined(_MSC_VER) && _MSC_VER >= 1910 // We have C++14, and are using VC >= 2017
#elif defined(HAVE_CXX14)
// is_base_of
template<typename Base, typename Derived>
@ -81,16 +85,8 @@ static constexpr bool is_base_of_v = std::is_base_of<Base, Derived>::value;
template<typename T, typename U>
static constexpr bool is_same_v = std::is_same<T, U>::value;
#else // We do not have C++14 or C++17
// is_base_of
template<typename Base, typename Derived>
using is_base_of_v = typename std::is_base_of<Base, Derived>::value;
// is_same
template<typename T, typename U>
using is_same_v = typename std::is_same<T, U>::value;
#endif // HAVE_CXX17
#endif
} // end namespace utils