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Fixup compilation of type trait aliases

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Turns out 'inline constexpr' is a C++17 feature. Fallback to 'static constexpr' with C++14,
except with VS < 2017, where variable templates are not supported.
This commit is contained in:
Charles Dang 2017-05-15 20:50:19 +11:00
parent 4d84f08354
commit 7e3b91ef8c
1 changed files with 19 additions and 14 deletions
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33
src/utils/type_trait_aliases.hpp
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@ -20,8 +20,8 @@
namespace utils
{
//
// These aliases are available in C++14. Forward to their declarations
// if building with that.
// These aliases are part of the standard starting with C++14.
// Forward to their declarations if appropriate.
//
#ifdef HAVE_CXX14
@ -32,7 +32,7 @@ using std::remove_const_t;
using std::remove_reference_t;
using std::remove_pointer_t;
#else
#else // We do not have C++14
// add_const
template<typename T>
@ -62,30 +62,35 @@ using remove_pointer_t = typename std::remove_pointer<T>::type;
//
// These aliases are part of the standard starting with C++17.
// Since we're not even near supporting that, we define them directly.
// They can be added to a conditional block once we have a define for 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.
//
#ifdef HAVE_CXX17
// MSVC 2013 doesn't support constexpr :(
#if 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
// is_base_of
template<typename Base, typename Derived>
static const bool is_base_of_v = std::is_base_of<Base, Derived>::value;
static constexpr bool is_base_of_v = std::is_base_of<Base, Derived>::value;
// is_same
template<typename T, typename U>
static const bool is_same_v = std::is_same<T, U>::value;
static constexpr bool is_same_v = std::is_same<T, U>::value;
#else
#else // We do not have C++14 or C++17
// is_base_of
template<typename Base, typename Derived>
inline constexpr bool is_base_of_v = std::is_base_of<Base, Derived>::value;
using is_base_of_v = typename std::is_base_of<Base, Derived>::value;
// is_same
template<typename T, typename U>
inline constexpr bool is_same_v = std::is_same<T, U>::value;
using is_same_v = typename std::is_same<T, U>::value;
#endif
}
#endif // HAVE_CXX17
} // end namespace utils