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Improved swap for optional<T>, co-written by Thorsten and Fernando: added support for tweaking whether swap should use T's default constructor. Added swap member function. Discussed at Boost developers' mailing list, "[optional] problems with swap()", http://lists.boost.org/Archives/boost/2008/04/135882.php

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[SVN r44766]
This commit is contained in:
Niels Dekker
2008-04-25 16:50:32 +00:00
parent 472a68c920
commit 66c366d18a
1 changed files with 75 additions and 29 deletions
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94
include/boost/optional/optional.hpp
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@ -1,4 +1,4 @@
// Copyright (C) 2003, Fernando Luis Cacciola Carballal.
// Copyright (C) 2003, 2008 Fernando Luis Cacciola Carballal.
//
// Use, modification, and distribution is subject to the Boost Software
// License, Version 1.0. (See accompanying file LICENSE_1_0.txt or copy at
@ -9,6 +9,9 @@
// You are welcome to contact the author at:
// fernando_cacciola@hotmail.com
//
// Revisions:
// 25 Apr 2008 (improved swap) Fernando Cacciola, Niels Dekker, Thorsten Ottosen
//
#ifndef BOOST_OPTIONAL_OPTIONAL_FLC_19NOV2002_HPP
#define BOOST_OPTIONAL_OPTIONAL_FLC_19NOV2002_HPP
@ -19,6 +22,7 @@
#include "boost/assert.hpp"
#include "boost/type.hpp"
#include "boost/type_traits/alignment_of.hpp"
#include "boost/type_traits/has_nothrow_constructor.hpp"
#include "boost/type_traits/type_with_alignment.hpp"
#include "boost/type_traits/remove_reference.hpp"
#include "boost/type_traits/is_reference.hpp"
@ -28,6 +32,7 @@
#include "boost/detail/reference_content.hpp"
#include "boost/none.hpp"
#include "boost/utility/compare_pointees.hpp"
#include "boost/utility/in_place_factory.hpp"
#include "boost/optional/optional_fwd.hpp"
@ -571,6 +576,14 @@ class optional : public optional_detail::optional_base<T>
return *this ;
}
void swap( optional & arg )
{
// allow for Koenig lookup
using std::swap ;
swap(*this, arg);
}
// Returns a reference to the value if this is initialized, otherwise,
// the behaviour is UNDEFINED
// No-throw
@ -878,44 +891,77 @@ namespace optional_detail {
#define BOOST_OPTIONAL_STD_SWAP_INTRODUCED_AT_NS_SCOPE
#endif
// optional's swap:
// If both are initialized, calls swap(T&, T&). If this swap throws, both will remain initialized but their values are now unspecified.
// If only one is initialized, calls U.reset(*I), THEN I.reset().
// If U.reset(*I) throws, both are left UNCHANGED (U is kept uinitialized and I is never reset)
// If both are uninitialized, do nothing (no-throw)
template<class T>
inline
void optional_swap ( optional<T>& x, optional<T>& y )
{
if ( !x && !!y )
template<bool use_default_constructor> struct swap_selector;
template<>
struct swap_selector<true>
{
x.reset(*y);
y.reset();
}
else if ( !!x && !y )
template<class T>
static void optional_swap ( optional<T>& x, optional<T>& y )
{
y.reset(*x);
x.reset();
}
else if ( !!x && !!y )
{
// GCC > 3.2 and all other compilers have the using declaration at function scope (FLC)
bool hasX = x;
bool hasY = y;
if ( !hasX && !hasY )
return;
if( !hasX )
x = boost::in_place();
else if ( !hasY )
y = boost::in_place();
// GCC > 3.2 and all other compilers have the using declaration at function scope (FLC)
#ifndef BOOST_OPTIONAL_STD_SWAP_INTRODUCED_AT_NS_SCOPE
// allow for Koenig lookup
using std::swap ;
#endif
swap(*x,*y);
if( !hasX )
y = boost::none ;
else if( !hasY )
x = boost::none ;
}
}
};
template<>
struct swap_selector<false>
{
template<class T>
static void optional_swap ( optional<T>& x, optional<T>& y )
{
if ( !x && !!y )
{
x = *y;
y = boost::none ;
}
else if ( !!x && !y )
{
y = *x ;
x = boost::none ;
}
else if ( !!x && !!y )
{
// GCC > 3.2 and all other compilers have the using declaration at function scope (FLC)
#ifndef BOOST_OPTIONAL_STD_SWAP_INTRODUCED_AT_NS_SCOPE
// allow for Koenig lookup
using std::swap ;
#endif
swap(*x,*y);
}
}
};
} // namespace optional_detail
template<class T>
struct optional_swap_should_use_default_constructor : has_nothrow_default_constructor<T> {} ;
template<class T> inline void swap ( optional<T>& x, optional<T>& y )
{
optional_detail::optional_swap(x,y);
optional_detail::swap_selector<optional_swap_should_use_default_constructor<T>::value>::optional_swap(x, y);
}
} // namespace boost
#endif