整理

include/boost/smart_ptr/detail/sp_cxx20_constexpr.hpp

@@ -0,0 +1,37 @@
+#ifndef BOOST_SMART_PTR_DETAIL_SP_CXX20_CONSTEXPR_HPP_INCLUDED
+#define BOOST_SMART_PTR_DETAIL_SP_CXX20_CONSTEXPR_HPP_INCLUDED
+
+// MS compatible compilers support #pragma once
+
+#if defined(_MSC_VER) && (_MSC_VER >= 1020)
+#pragma once
+#endif
+
+//  detail/sp_noexcept.hpp
+//
+//  Copyright 2025 Mathias Stearn
+//
+//  Distributed under the Boost Software License, Version 1.0.
+//  See accompanying file LICENSE_1_0.txt or copy at
+//  http://www.boost.org/LICENSE_1_0.txt
+
+
+// This macro is used to mark functions as constexpr if the compiler supports
+// constexpr destructors. Since you can't have a constexpr smart pointer object,
+// everything except null constructors are guided behind this macro. Because
+// this also guards a use of dynamic_cast, we need to check for its availability
+// as well. It isn't worth splitting out since all known compilers that support
+// constexpr dynamic_cast also support constexpr destructors.
+//
+// WARNING: This does not check for changing active member of a union in
+// constant expressions which is allowed in C++20. If that is needed, we
+// need to raise the checked version to 202002L.
+#if defined(__cpp_constexpr_dynamic_alloc) && __cpp_constexpr_dynamic_alloc >= 201907L \
+    && defined(__cpp_constexpr) && __cpp_constexpr >= 201907L
+#define BOOST_SP_CXX20_CONSTEXPR constexpr
+#else
+#define BOOST_SP_CXX20_CONSTEXPR
+#define BOOST_SP_NO_CXX20_CONSTEXPR
+#endif
+
+#endif // #ifndef BOOST_SMART_PTR_DETAIL_SP_CXX20_CONSTEXPR_HPP_INCLUDED