smart_ptr/detail/sp_cxx20_constexpr.hpp

0001 #ifndef BOOST_SMART_PTR_DETAIL_SP_CXX20_CONSTEXPR_HPP_INCLUDED
0002 #define BOOST_SMART_PTR_DETAIL_SP_CXX20_CONSTEXPR_HPP_INCLUDED
0003
0004 // MS compatible compilers support #pragma once
0005
0006 #if defined(_MSC_VER) && (_MSC_VER >= 1020)
0007 #pragma once
0008 #endif
0009
0010 //  detail/sp_noexcept.hpp
0011 //
0012 //  Copyright 2025 Mathias Stearn
0013 //
0014 //  Distributed under the Boost Software License, Version 1.0.
0015 //  See accompanying file LICENSE_1_0.txt or copy at
0016 //  http://www.boost.org/LICENSE_1_0.txt
0017
0018
0019 // This macro is used to mark functions as constexpr if the compiler supports
0020 // constexpr destructors. Since you can't have a constexpr smart pointer object,
0021 // everything except null constructors are guided behind this macro. Because
0022 // this also guards a use of dynamic_cast, we need to check for its availability
0023 // as well. It isn't worth splitting out since all known compilers that support
0024 // constexpr dynamic_cast also support constexpr destructors.
0025 //
0026 // WARNING: This does not check for changing active member of a union in
0027 // constant expressions which is allowed in C++20. If that is needed, we
0028 // need to raise the checked version to 202002L.
0029 #if defined(__cpp_constexpr_dynamic_alloc) && __cpp_constexpr_dynamic_alloc >= 201907L \
0030     && defined(__cpp_constexpr) && __cpp_constexpr >= 201907L
0031 #define BOOST_SP_CXX20_CONSTEXPR constexpr
0032 #else
0033 #define BOOST_SP_CXX20_CONSTEXPR
0034 #define BOOST_SP_NO_CXX20_CONSTEXPR
0035 #endif
0036
0037 #endif // #ifndef BOOST_SMART_PTR_DETAIL_SP_CXX20_CONSTEXPR_HPP_INCLUDED