histogram/detail/static_if.hpp

0001 // Copyright 2018-2019 Hans Dembinski
0002 //
0003 // Distributed under the Boost Software License, Version 1.0.
0004 // (See accompanying file LICENSE_1_0.txt
0005 // or copy at http://www.boost.org/LICENSE_1_0.txt)
0006
0007 #ifndef BOOST_HISTOGRAM_DETAIL_STATIC_IF_HPP
0008 #define BOOST_HISTOGRAM_DETAIL_STATIC_IF_HPP
0009
0010 #include <type_traits>
0011 #include <utility>
0012
0013 namespace boost {
0014 namespace histogram {
0015 namespace detail {
0016
0017 template <class T, class F, class... Args>
0018 constexpr decltype(auto) static_if_impl(
0019     std::true_type, T&& t, F&&,
0020     Args&&... args) noexcept(noexcept(std::declval<T>()(std::declval<Args>()...))) {
0021   return std::forward<T>(t)(std::forward<Args>(args)...);
0022 }
0023
0024 template <class T, class F, class... Args>
0025 constexpr decltype(auto) static_if_impl(
0026     std::false_type, T&&, F&& f,
0027     Args&&... args) noexcept(noexcept(std::declval<F>()(std::declval<Args>()...))) {
0028   return std::forward<F>(f)(std::forward<Args>(args)...);
0029 }
0030
0031 template <bool B, class... Ts>
0032 constexpr decltype(auto) static_if_c(Ts&&... ts) noexcept(
0033     noexcept(static_if_impl(std::integral_constant<bool, B>{}, std::declval<Ts>()...))) {
0034   return static_if_impl(std::integral_constant<bool, B>{}, std::forward<Ts>(ts)...);
0035 }
0036
0037 template <class Bool, class... Ts>
0038 constexpr decltype(auto) static_if(Ts&&... ts) noexcept(
0039     noexcept(static_if_impl(Bool{}, std::declval<Ts>()...))) {
0040   return static_if_impl(Bool{}, std::forward<Ts>(ts)...);
0041 }
0042
0043 } // namespace detail
0044 } // namespace histogram
0045 } // namespace boost
0046
0047 #endif