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Make use of C++17 if constexpr if available
* Supply a polyfill if it is not available
This commit is contained in:
Denis Blank
parent
d30814c2ff
commit
14ebb40756
@ -52,15 +52,15 @@
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// Detect if the whole standard is available
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#if (defined(_MSC_VER) && defined(_HAS_CXX17) && _HAS_CXX17) || \
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(__cplusplus >= 201703L)
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#define CONTINUABLE_HAS_CXX17_CONSTEXPR_IF
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#define CONTINUABLE_HAS_CXX17_IF_CONSTEXPR
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#define CONTINUABLE_HAS_CXX17_DISJUNCTION
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#define CONTINUABLE_HAS_CXX17_CONJUNCTION
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#else
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// Generic feature detection based on __has_feature
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#if defined(__has_feature)
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#if !defined(CONTINUABLE_HAS_CXX17_CONSTEXPR_IF) && \
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#if !defined(CONTINUABLE_HAS_CXX17_IF_CONSTEXPR) && \
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__has_feature(cxx_if_constexpr)
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#define CONTINUABLE_HAS_CXX17_CONSTEXPR_IF
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#define CONTINUABLE_HAS_CXX17_IF_CONSTEXPR
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#endif
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#endif
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@ -102,32 +102,78 @@ struct deduce_to_void : std::common_type<void> {};
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template <typename... T>
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using void_t = typename detail::deduce_to_void<T...>::type;
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#if defined(CONTINUABLE_HAS_CXX17_IF_CONSTEXPR)
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#define CONTINUABLE_IF_CONSTEXPR_SELECT_2(EXPR, TRUE_BRANCH) \
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[&](auto) mutable { \
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if constexpr (EXPR) { \
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TRUE_BRANCH \
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} \
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}(0)
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#define CONTINUABLE_IF_CONSTEXPR_SELECT_3(EXPR, TRUE_BRANCH, FALSE_BRANCH) \
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[&](auto) mutable { \
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if constexpr (EXPR) { \
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TRUE_BRANCH \
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} else { \
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FALSE_BRANCH \
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} \
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}(0)
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#else
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namespace detail {
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template <typename Type, typename TrueCallback>
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constexpr void static_if_impl(std::true_type, Type&& type,
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TrueCallback&& trueCallback) {
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std::forward<TrueCallback>(trueCallback)(std::forward<Type>(type));
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template <typename TrueCallback>
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constexpr void static_if_impl(std::true_type, TrueCallback&& trueCallback) {
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std::forward<TrueCallback>(trueCallback)(0);
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}
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template <typename Type, typename TrueCallback>
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constexpr void static_if_impl(std::false_type, Type&& /*type*/,
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template <typename TrueCallback>
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constexpr void static_if_impl(std::false_type,
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TrueCallback&& /*trueCallback*/) {
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}
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template <typename Type, typename TrueCallback, typename FalseCallback>
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constexpr auto static_if_impl(std::true_type, Type&& type,
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TrueCallback&& trueCallback,
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template <typename TrueCallback, typename FalseCallback>
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constexpr auto static_if_impl(std::true_type, TrueCallback&& trueCallback,
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FalseCallback&& /*falseCallback*/) {
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return std::forward<TrueCallback>(trueCallback)(std::forward<Type>(type));
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return std::forward<TrueCallback>(trueCallback)(0);
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}
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template <typename Type, typename TrueCallback, typename FalseCallback>
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constexpr auto static_if_impl(std::false_type, Type&& type,
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TrueCallback&& /*trueCallback*/,
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template <typename TrueCallback, typename FalseCallback>
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constexpr auto static_if_impl(std::false_type, TrueCallback&& /*trueCallback*/,
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FalseCallback&& falseCallback) {
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return std::forward<FalseCallback>(falseCallback)(std::forward<Type>(type));
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return std::forward<FalseCallback>(falseCallback)(0);
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}
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} // namespace detail
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#define CONTINUABLE_IF_CONSTEXPR_SELECT_2(EXPR, TRUE_BRANCH) \
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cti::detail::traits::detail::static_if_impl( \
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std::integral_constant<bool, EXPR>{}, [&](auto) mutable { TRUE_BRANCH })
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#define CONTINUABLE_IF_CONSTEXPR_SELECT_3(EXPR, TRUE_BRANCH, FALSE_BRANCH) \
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cti::detail::traits::detail::static_if_impl( \
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std::integral_constant<bool, EXPR>{}, [&](auto) mutable { TRUE_BRANCH }, \
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[&](auto) { FALSE_BRANCH })
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#endif // CONTINUABLE_HAS_CXX17_IF_CONSTEXPR
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// https://stackoverflow.com/questions/16374776/macro-overloading
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// compute number of (variadic) macro arguments from
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// http://groups.google.com/group/comp.std.c/browse_thread/thread/77ee8c8f92e4a3fb/346fc464319b1ee5?pli=1
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#define CONTINUABLE_EXPAND(X) X // for MSVC10 compatibility
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#define CONTINUABLE_PP_NARG(...) \
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CONTINUABLE_EXPAND(CONTINUABLE_PP_NARG_(__VA_ARGS__, CONTINUABLE_PP_RSEQ_N()))
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#define CONTINUABLE_PP_NARG_(...) \
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CONTINUABLE_EXPAND(CONTINUABLE_PP_ARG_N(__VA_ARGS__))
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#define CONTINUABLE_PP_ARG_N(_1, _2, _3, N, ...) N
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#define CONTINUABLE_PP_RSEQ_N() 3, 2, 1, 0
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#define CONTINUABLE_IF_CONSTEXPR_SELECT_(N) CONTINUABLE_IF_CONSTEXPR_SELECT_##N
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#define CONTINUABLE_IF_CONSTEXPR_SELECT_EVAL(N) \
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CONTINUABLE_IF_CONSTEXPR_SELECT_(N)
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/// Polyfill for C++17 if constexpr, uses if constexpr when available,
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/// otherwise a polyfill through lambdas is used.
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#define CONTINUABLE_IF_CONSTEXPR(...) \
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CONTINUABLE_EXPAND(CONTINUABLE_IF_CONSTEXPR_SELECT_EVAL( \
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CONTINUABLE_EXPAND(CONTINUABLE_PP_NARG(__VA_ARGS__)))(__VA_ARGS__))
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namespace detail {
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/// Evaluates to the size of the given tuple like type,
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// / if the type has no static size it will be one.
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template <typename T, typename Enable = void>
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@ -159,27 +205,6 @@ constexpr auto sequence_of(identity<T>) noexcept {
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return std::make_index_sequence<size>();
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}
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/// Invokes the callback only if the given type matches the check
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template <typename Type, typename Check, typename TrueCallback>
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constexpr void static_if(Type&& type, Check&& check,
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TrueCallback&& trueCallback) {
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detail::static_if_impl(std::forward<Check>(check)(type),
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std::forward<Type>(type),
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std::forward<TrueCallback>(trueCallback));
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}
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/// Invokes the callback only if the given type matches the check
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template <typename Type, typename Check, typename TrueCallback,
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typename FalseCallback>
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constexpr auto static_if(Type&& type, Check&& check,
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TrueCallback&& trueCallback,
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FalseCallback&& falseCallback) {
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return detail::static_if_impl(std::forward<Check>(check)(type),
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std::forward<Type>(type),
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std::forward<TrueCallback>(trueCallback),
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std::forward<FalseCallback>(falseCallback));
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}
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/// Calls the given unpacker with the content of the given sequence
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template <typename U, std::size_t... I>
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constexpr decltype(auto) unpack(std::integer_sequence<std::size_t, I...>,
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@ -266,10 +266,4 @@ private:
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} // namespace detail
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} // namespace cti
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#ifdef CONTINUABLE_CONSTEXPR_IF
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#define CONTINUABLE_CONSTEXPR_IF(EXPR, TRUE_BRANCH, FALSE_BRANCH)
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#else
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#define CONTINUABLE_CONSTEXPR_IF(EXPR, TRUE_BRANCH, FALSE_BRANCH)
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#endif // CONTINUABLE_CONSTEXPR_IF
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#endif // CONTINUABLE_DETAIL_UTIL_HPP_INCLUDED
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