forked from boostorg/utility
117 lines
2.8 KiB
C++
117 lines
2.8 KiB
C++
// (C) Copyright 2002-2008, Fernando Luis Cacciola Carballal.
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//
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// Distributed under the Boost Software License, Version 1.0. (See
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// accompanying file LICENSE_1_0.txt or copy at
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// http://www.boost.org/LICENSE_1_0.txt)
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//
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// 21 Ago 2002 (Created) Fernando Cacciola
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// 19 Jan 2008 (Worked around compiler bugs, added initialized_value) Fernando Cacciola, Niels Dekker
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//
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#ifndef BOOST_UTILITY_VALUE_INIT_21AGO2002_HPP
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#define BOOST_UTILITY_VALUE_INIT_21AGO2002_HPP
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// Note: The implementation of boost::value_initialized had to deal with the
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// fact that various compilers haven't fully implemented value-initialization.
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// The constructor of boost::value_initialized<T> works around these compiler
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// issues, by clearing the bytes of T, before constructing the T object it
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// contains. More details on these issues are at libs/utility/value_init.htm
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#include <boost/aligned_storage.hpp>
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#include <boost/detail/workaround.hpp>
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#include <boost/type_traits/cv_traits.hpp>
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#include <boost/type_traits/alignment_of.hpp>
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#include <cstring>
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#include <new>
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namespace boost {
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template<class T>
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class value_initialized
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{
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private :
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struct wrapper
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{
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#if !BOOST_WORKAROUND(__BORLANDC__, BOOST_TESTED_AT(0x592))
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typename
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#endif
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remove_const<T>::type data;
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};
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mutable aligned_storage<sizeof(wrapper), alignment_of<wrapper>::value> x;
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public :
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value_initialized()
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{
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std::memset(x.address(), 0, sizeof(x));
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#ifdef BOOST_MSVC
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#pragma warning(push)
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#if _MSC_VER >= 1310
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// When using MSVC 7.1 or higher, the following placement new expression may trigger warning C4345:
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// "behavior change: an object of POD type constructed with an initializer of the form ()
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// will be default-initialized". It is safe to ignore this warning when using value_initialized.
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#pragma warning(disable: 4345)
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#endif
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#endif
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new (x.address()) wrapper();
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#ifdef BOOST_MSVC
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#pragma warning(pop)
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#endif
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}
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value_initialized(value_initialized const & arg)
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{
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new (x.address()) wrapper( *static_cast<wrapper const *>(arg.x.address()) );
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}
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value_initialized & operator=(value_initialized const & arg)
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{
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T const & arg_data = arg.data();
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this->data() = arg_data;
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return *this;
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}
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~value_initialized()
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{
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static_cast<wrapper *>(x.address())->wrapper::~wrapper();
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}
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T& data() const
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{
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return static_cast<wrapper *>(x.address())->data;
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}
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operator T&() const { return this->data(); }
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} ;
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template<class T>
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T const& get ( value_initialized<T> const& x )
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{
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return x.data() ;
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}
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template<class T>
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T& get ( value_initialized<T>& x )
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{
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return x.data() ;
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}
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class initialized_value
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{
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public :
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template <class T> operator T() const
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{
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return get( value_initialized<T>() );
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}
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};
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} // namespace boost
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#endif
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