drop c++03 support

include/boost/implicit_cast.hpp

@@ -11,22 +11,9 @@
 # pragma once
 #endif
 
-#include <boost/config/pragma_message.hpp>
-#if defined(BOOST_NO_CXX11_RVALUE_REFERENCES) || \
-    defined(BOOST_NO_CXX11_AUTO_DECLARATIONS) || \
-    defined(BOOST_NO_CXX11_CONSTEXPR) || \
-    defined(BOOST_NO_CXX11_NULLPTR) || \
-    defined(BOOST_NO_CXX11_NOEXCEPT) || \
-    defined(BOOST_NO_CXX11_DEFAULTED_FUNCTIONS) || \
-    defined(BOOST_NO_CXX11_FINAL) || \
-    defined(BOOST_NO_CXX11_ALIGNOF) || \
-    defined(BOOST_NO_CXX11_STATIC_ASSERT) || \
-    defined(BOOST_NO_CXX11_SMART_PTR) || \
-    defined(BOOST_NO_CXX11_HDR_INITIALIZER_LIST) || \
-    defined(BOOST_NO_CXX11_HDR_TYPE_TRAITS)
-
-BOOST_PRAGMA_MESSAGE("C++03 support is deprecated in Boost.Conversion 1.82 and will be removed in Boost.Conversion 1.84.")
 
+#if defined(BOOST_NO_CXX11_CONSTEXPR)
+#error C++03 support is removed in Boost.Conversion 1.84
 #endif
 
 namespace boost {
@@ -46,7 +33,7 @@ template<class T> struct icast_identity
 // The use of identity creates a non-deduced form, so that the
 // explicit template argument must be supplied
 template <typename T>
-BOOST_CONSTEXPR inline T implicit_cast (typename boost::detail::icast_identity<T>::type x) {
+constexpr T implicit_cast (typename boost::detail::icast_identity<T>::type x) {
     return x;
 }