| // (C) Copyright 2002-2008, Fernando Luis Cacciola Carballal. |
| // |
| // 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) |
| // |
| // 21 Ago 2002 (Created) Fernando Cacciola |
| // 24 Dec 2007 (Refactored and worked around various compiler bugs) Fernando Cacciola, Niels Dekker |
| // 23 May 2008 (Fixed operator= const issue, added initialized_value) Niels Dekker, Fernando Cacciola |
| // 21 Ago 2008 (Added swap) Niels Dekker, Fernando Cacciola |
| // |
| #ifndef BOOST_UTILITY_VALUE_INIT_21AGO2002_HPP |
| #define BOOST_UTILITY_VALUE_INIT_21AGO2002_HPP |
| |
| // Note: The implementation of boost::value_initialized had to deal with the |
| // fact that various compilers haven't fully implemented value-initialization. |
| // The constructor of boost::value_initialized<T> works around these compiler |
| // 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/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> |
| |
| namespace boost { |
| |
| template<class T> |
| class value_initialized |
| { |
| private : |
| struct wrapper |
| { |
| #if !BOOST_WORKAROUND(__BORLANDC__, BOOST_TESTED_AT(0x592)) |
| typename |
| #endif |
| remove_const<T>::type data; |
| }; |
| |
| mutable |
| #if !BOOST_WORKAROUND(__BORLANDC__, BOOST_TESTED_AT(0x592)) |
| typename |
| #endif |
| aligned_storage<sizeof(wrapper), alignment_of<wrapper>::value>::type x; |
| |
| wrapper * wrapper_address() const |
| { |
| return static_cast<wrapper *>( static_cast<void*>(&x)); |
| } |
| |
| public : |
| |
| value_initialized() |
| { |
| std::memset(&x, 0, sizeof(x)); |
| #ifdef BOOST_MSVC |
| #pragma warning(push) |
| #if _MSC_VER >= 1310 |
| // When using MSVC 7.1 or higher, the following placement new expression may trigger warning C4345: |
| // "behavior change: an object of POD type constructed with an initializer of the form () |
| // will be default-initialized". It is safe to ignore this warning when using value_initialized. |
| #pragma warning(disable: 4345) |
| #endif |
| #endif |
| new (wrapper_address()) wrapper(); |
| #ifdef BOOST_MSVC |
| #pragma warning(pop) |
| #endif |
| } |
| |
| value_initialized(value_initialized const & arg) |
| { |
| new (wrapper_address()) wrapper( static_cast<wrapper const &>(*(arg.wrapper_address()))); |
| } |
| |
| value_initialized & operator=(value_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; |
| } |
| |
| ~value_initialized() |
| { |
| wrapper_address()->wrapper::~wrapper(); |
| } |
| |
| T& data() const |
| { |
| return wrapper_address()->data; |
| } |
| |
| void swap(value_initialized & arg) |
| { |
| ::boost::swap( this->data(), arg.data() ); |
| } |
| |
| operator T&() const { return this->data(); } |
| |
| } ; |
| |
| |
| |
| template<class T> |
| T const& get ( value_initialized<T> const& x ) |
| { |
| return x.data() ; |
| } |
| template<class T> |
| T& get ( value_initialized<T>& x ) |
| { |
| return x.data() ; |
| } |
| |
| template<class T> |
| void swap ( value_initialized<T> & lhs, value_initialized<T> & rhs ) |
| { |
| lhs.swap(rhs) ; |
| } |
| |
| |
| class initialized_value_t |
| { |
| public : |
| |
| template <class T> operator T() const |
| { |
| return get( value_initialized<T>() ); |
| } |
| }; |
| |
| initialized_value_t const initialized_value = {} ; |
| |
| |
| } // namespace boost |
| |
| |
| #endif |