Extract throws into its own header

include/boost/system/detail/throws.hpp

@@ -0,0 +1,59 @@
+#ifndef BOOST_SYSTEM_DETAIL_THROWS_HPP_INCLUDED
+#define BOOST_SYSTEM_DETAIL_THROWS_HPP_INCLUDED
+
+//  Copyright Beman Dawes 2006, 2007
+//  Copyright Christoper Kohlhoff 2007
+//  Copyright Peter Dimov 2017, 2018
+//
+//  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)
+//
+//  See library home page at http://www.boost.org/libs/system
+
+namespace boost
+{
+
+namespace system
+{
+
+class error_code;
+
+} // namespace system
+
+// boost::throws()
+
+namespace detail
+{
+
+//  Misuse of the error_code object is turned into a noisy failure by
+//  poisoning the reference. This particular implementation doesn't
+//  produce warnings or errors from popular compilers, is very efficient
+//  (as determined by inspecting generated code), and does not suffer
+//  from order of initialization problems. In practice, it also seems
+//  cause user function error handling implementation errors to be detected
+//  very early in the development cycle.
+
+inline system::error_code* throws()
+{
+    // See github.com/boostorg/system/pull/12 by visigoth for why the return
+    // is poisoned with nonzero rather than (0). A test, test_throws_usage(),
+    // has been added to error_code_test.cpp, and as visigoth mentioned it
+    // fails on clang for release builds with a return of 0 but works fine
+    // with (1).
+    // Since the undefined behavior sanitizer (-fsanitize=undefined) does not
+    // allow a reference to be formed to the unaligned address of (1), we use
+    // (8) instead.
+
+    return reinterpret_cast<system::error_code*>(8);
+}
+
+} // namespace detail
+
+inline system::error_code& throws()
+{
+    return *detail::throws();
+}
+
+} // namespace boost
+
+#endif // #ifndef BOOST_SYSTEM_DETAIL_THROWS_HPP_INCLUDED

include/boost/system/error_code.hpp

@@ -19,6 +19,7 @@
 #include <boost/system/detail/enable_if.hpp>
 #include <boost/system/detail/error_condition.hpp>
 #include <boost/system/detail/error_code.hpp>
+#include <boost/system/detail/throws.hpp>
 #include <boost/system/api_config.hpp>
 #include <boost/system/detail/config.hpp>
 #include <boost/cstdint.hpp>
@@ -48,40 +49,6 @@ class error_condition;    // portable generic values defined below, but ultimate
 
 }  // namespace system
 
-// boost::throws()
-
-namespace detail
-{
-
-//  Misuse of the error_code object is turned into a noisy failure by
-//  poisoning the reference. This particular implementation doesn't
-//  produce warnings or errors from popular compilers, is very efficient
-//  (as determined by inspecting generated code), and does not suffer
-//  from order of initialization problems. In practice, it also seems
-//  cause user function error handling implementation errors to be detected
-//  very early in the development cycle.
-
-inline system::error_code* throws()
-{
-    // See github.com/boostorg/system/pull/12 by visigoth for why the return
-    // is poisoned with nonzero rather than (0). A test, test_throws_usage(),
-    // has been added to error_code_test.cpp, and as visigoth mentioned it
-    // fails on clang for release builds with a return of 0 but works fine
-    // with (1).
-    // Since the undefined behavior sanitizer (-fsanitize=undefined) does not
-    // allow a reference to be formed to the unaligned address of (1), we use
-    // (8) instead.
-
-    return reinterpret_cast<system::error_code*>(8);
-}
-
-} // namespace detail
-
-inline system::error_code& throws()
-{
-    return *detail::throws();
-}
-
 // non-member functions of error_code and error_condition
 
 namespace system