Use a base class to apply the memset workaround to avoid dependency on TypeTraits

include/boost/utility/value_init.hpp

@@ -1,4 +1,5 @@
 // (C) Copyright 2002-2008, Fernando Luis Cacciola Carballal.
+// Copyright 2020 Peter Dimov
 //
 // Distributed under the Boost Software License, Version 1.0. (See
 // accompanying file LICENSE_1_0.txt or copy at
@@ -21,15 +22,10 @@
 // issues, by clearing the bytes of T, before constructing the T object it
 // contains. More details on these issues are at libs/utility/value_init.htm
 
-#include <boost/aligned_storage.hpp>
 #include <boost/config.hpp> // For BOOST_NO_COMPLETE_VALUE_INITIALIZATION.
-#include <boost/detail/workaround.hpp>
-#include <boost/static_assert.hpp>
-#include <boost/type_traits/cv_traits.hpp>
-#include <boost/type_traits/alignment_of.hpp>
 #include <boost/swap.hpp>
 #include <cstring>
-#include <new>
+#include <cstddef>
 
 #ifdef BOOST_MSVC
 #pragma warning(push)
@@ -39,6 +35,8 @@
 // It is safe to ignore the following MSVC warning, which may pop up when T is 
 // a const type: "warning C4512: assignment operator could not be generated".
 #pragma warning(disable: 4512)
+// C4355: 'this' : used in base member initializer list
+#pragma warning(disable: 4355)
 #endif
 
 #ifdef BOOST_NO_COMPLETE_VALUE_INITIALIZATION
@@ -60,92 +58,58 @@
 
 namespace boost {
 
-template<class T>
-class initialized
-{
-  private :
-    struct wrapper
-    {
-#if !BOOST_WORKAROUND(BOOST_BORLANDC, BOOST_TESTED_AT(0x592))
-      typename
-#endif 
-      remove_const<T>::type data;
+namespace detail {
 
-      BOOST_GPU_ENABLED
-      wrapper()
-      :
-      data()
+  struct zero_init
+  {
+    zero_init()
     {
     }
 
-      BOOST_GPU_ENABLED
-      wrapper(T const & arg)
-      :
-      data(arg)
+    zero_init( void * p, std::size_t n )
     {
+      std::memset( p, 0, n );
     }
   };
 
-    mutable
-#if !BOOST_WORKAROUND(BOOST_BORLANDC, BOOST_TESTED_AT(0x592))
-      typename
-#endif 
-      aligned_storage<sizeof(wrapper), alignment_of<wrapper>::value>::type x;
+} // namespace detail
 
-    BOOST_GPU_ENABLED
-    wrapper * wrapper_address() const
+template<class T>
+class initialized
+#if BOOST_DETAIL_VALUE_INIT_WORKAROUND
+  : detail::zero_init
+#endif
 {
-      return static_cast<wrapper *>( static_cast<void*>(&x));
-    }
+  private:
+
+    T data_;
 
   public :
 
     BOOST_GPU_ENABLED
-    initialized()
-    {
+    initialized():
 #if BOOST_DETAIL_VALUE_INIT_WORKAROUND
-      std::memset(&x, 0, sizeof(x));
+      zero_init( this, sizeof(*this) ),
 #endif
-      new (wrapper_address()) wrapper();
+      data_()
+    {
     }
 
     BOOST_GPU_ENABLED
-    initialized(initialized const & arg)
+    explicit initialized(T const & arg): data_( arg )
     {
-      new (wrapper_address()) wrapper( static_cast<wrapper const &>(*(arg.wrapper_address())));
-    }
-
-    BOOST_GPU_ENABLED
-    explicit initialized(T const & arg)
-    {
-      new (wrapper_address()) wrapper(arg);
-    }
-
-    BOOST_GPU_ENABLED
-    initialized & operator=(initialized const & arg)
-    {
-      // Assignment is only allowed when T is non-const.
-      BOOST_STATIC_ASSERT( ! is_const<T>::value );
-      *wrapper_address() = static_cast<wrapper const &>(*(arg.wrapper_address()));
-      return *this;
-    }
-
-    BOOST_GPU_ENABLED
-    ~initialized()
-    {
-      wrapper_address()->wrapper::~wrapper();
     }
 
     BOOST_GPU_ENABLED
     T const & data() const
     {
-      return wrapper_address()->data;
+      return data_;
     }
 
     BOOST_GPU_ENABLED
     T& data()
     {
-      return wrapper_address()->data;
+      return data_;
     }
 
     BOOST_GPU_ENABLED
@@ -157,13 +121,13 @@ class initialized
     BOOST_GPU_ENABLED
     operator T const &() const
     {
-      return wrapper_address()->data;
+      return data_;
     }
 
     BOOST_GPU_ENABLED
     operator T&()
     {
-      return wrapper_address()->data;
+      return data_;
     }
 
 } ;

test/value_init_test.cpp

@@ -22,6 +22,7 @@
 #endif
 
 #include <boost/core/lightweight_test.hpp>
+#include <boost/config/workaround.hpp>
 
 //
 // Sample POD type