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 		<h1><A href="../../index.htm"><img src="../../boost.png" alt="boost.png (6897 bytes)" align="middle" width="277" height="86"
 					border="0"></A>Smart Pointer Changes</h1>
 		<p>The February 2002 change to the Boost smart pointers introduced a number of
 			changes. Since the previous version of the smart pointers was in use for a long
 			time, it's useful to have a detailed list of what changed from a library user's
 			point of view.</p>
 		<p>Note that for compilers that don't support member templates well enough, a
 			separate implementation is used that lacks many of the new features and is more
 			like the old version.</p>
 		<h2>Features Requiring Code Changes to Take Advantage</h2>
 		<ul>
 			<li>
 				The smart pointer class templates now each have their own header file. For
 				compatibility, the <a href="../../boost/smart_ptr.hpp">&lt;boost/smart_ptr.hpp&gt;</a>
 			header now includes the headers for the four classic smart pointer class
 			templates.
 			<li>
 				The <b>weak_ptr</b>
 			template was added.
 			<li>
 				The new <b>shared_ptr</b> and <b>shared_array</b> relax the requirement that
 				the pointed-to object's destructor must be visible when instantiating the <b>shared_ptr</b>
 			destructor. This makes it easier to have shared_ptr members in classes without
 			explicit destructors.
 			<li>
 				A custom deallocator can be passed in when creating a <b>shared_ptr</b> or <b>shared_array</b>.
 			<li>
 				<b>shared_static_cast</b> and <b>shared_dynamic_cast</b> function templates are
 				provided which work for <b>shared_ptr</b> and <b>weak_ptr</b> as <b>static_cast</b>
 				and <b>dynamic_cast</b>
 			do for pointers.
 			<li>
 				The self-assignment misfeature has been removed from <b>shared_ptr::reset</b>,
 				although it is still present in <b>scoped_ptr</b>, and in <b>std::auto_ptr</b>.
 				Calling <b>reset</b> with a pointer to the object that's already owned by the <b>shared_ptr</b>
 			results in undefined behavior (an assertion, or eventually a double-delete if
 			assertions are off).
 			<li>
 				The <b>BOOST_SMART_PTR_CONVERSION</b>
 			feature has been removed.
 			<li>
 				<b>shared_ptr&lt;void&gt;</b> is now allowed.</li>
 		</ul>
 		<h2>Features That Improve Robustness</h2>
 		<ul>
 			<li>
 				The manipulation of use counts is now <a name="threadsafe">thread safe</a> on
 				Windows, Linux, and platforms that support pthreads. See the <a href="../../boost/detail/atomic_count.hpp">
 					&lt;boost/detail/atomic_count.hpp&gt;</a>
 			file for details
 			<li>
 				The new shared_ptr will always delete the object using the pointer it was
 				originally constructed with. This prevents subtle problems that could happen if
 				the last <b>shared_ptr</b> was a pointer to a sub-object of a class that did
 				not have a virtual destructor.</li>
 		</ul>
 		<h2>Implementation Details</h2>
 		<ul>
 			<li>
 				Some bugs in the assignment operator implementations and in <b>reset</b>
 			have been fixed by using the "copy and swap" idiom.
 			<li>
 				Assertions have been added to check preconditions of various functions;
 				however, since these use the new <a href="../../boost/assert.hpp">&lt;boost/assert.hpp&gt;</a>
 			header, the assertions are disabled by default.
 			<li>
 				The partial specialization of <b>std::less</b> has been replaced by <b>operator&lt;</b>
 			overloads which accomplish the same thing without relying on undefined
 			behavior.
 			<li>
 				The incorrect overload of <b>std::swap</b> has been replaced by <b>boost::swap</b>,
 				which has many of the same advantages for generic programming but does not
 				violate the C++ standard.</li>
 		</ul>
 		<hr>
 		<p>Revised 1 February 2002</p>
 		<p><small>Copyright 2002 Darin Adler. Distributed under the Boost Software License, Version
 				1.0. See accompanying file <A href="../../LICENSE_1_0.txt">LICENSE_1_0.txt</A> or
 				copy at <A href="http://www.boost.org/LICENSE_1_0.txt">http://www.boost.org/LICENSE_1_0.txt</A>.</small></p>
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	<html>
	<head>
	<title>Smart Pointer Changes</title>
	<meta http-equiv="Content-Type" content="text/html; charset=iso-8859-1">
	</head>
	<body bgcolor="#ffffff" text="#000000">
	<h1><A href="../../index.htm"><img src="../../boost.png" alt="boost.png (6897 bytes)" align="middle" width="277" height="86"
	border="0"></A>Smart Pointer Changes</h1>
	<p>The February 2002 change to the Boost smart pointers introduced a number of
	changes. Since the previous version of the smart pointers was in use for a long
	time, it's useful to have a detailed list of what changed from a library user's
	point of view.</p>
	<p>Note that for compilers that don't support member templates well enough, a
	separate implementation is used that lacks many of the new features and is more
	like the old version.</p>
	<h2>Features Requiring Code Changes to Take Advantage</h2>
	<ul>
	<li>
	The smart pointer class templates now each have their own header file. For
	compatibility, the <a href="../../boost/smart_ptr.hpp"><boost/smart_ptr.hpp></a>
	header now includes the headers for the four classic smart pointer class
	templates.
	<li>
	The <b>weak_ptr</b>
	template was added.
	<li>
	The new <b>shared_ptr</b> and <b>shared_array</b> relax the requirement that
	the pointed-to object's destructor must be visible when instantiating the <b>shared_ptr</b>
	destructor. This makes it easier to have shared_ptr members in classes without
	explicit destructors.
	<li>
	A custom deallocator can be passed in when creating a <b>shared_ptr</b> or <b>shared_array</b>.
	<li>
	<b>shared_static_cast</b> and <b>shared_dynamic_cast</b> function templates are
	provided which work for <b>shared_ptr</b> and <b>weak_ptr</b> as <b>static_cast</b>
	and <b>dynamic_cast</b>
	do for pointers.
	<li>
	The self-assignment misfeature has been removed from <b>shared_ptr::reset</b>,
	although it is still present in <b>scoped_ptr</b>, and in <b>std::auto_ptr</b>.
	Calling <b>reset</b> with a pointer to the object that's already owned by the <b>shared_ptr</b>
	results in undefined behavior (an assertion, or eventually a double-delete if
	assertions are off).
	<li>
	The <b>BOOST_SMART_PTR_CONVERSION</b>
	feature has been removed.
	<li>
	<b>shared_ptr<void></b> is now allowed.</li>
	</ul>
	<h2>Features That Improve Robustness</h2>
	<ul>
	<li>
	The manipulation of use counts is now <a name="threadsafe">thread safe</a> on
	Windows, Linux, and platforms that support pthreads. See the <a href="../../boost/detail/atomic_count.hpp">
	<boost/detail/atomic_count.hpp></a>
	file for details
	<li>
	The new shared_ptr will always delete the object using the pointer it was
	originally constructed with. This prevents subtle problems that could happen if
	the last <b>shared_ptr</b> was a pointer to a sub-object of a class that did
	not have a virtual destructor.</li>
	</ul>
	<h2>Implementation Details</h2>
	<ul>
	<li>
	Some bugs in the assignment operator implementations and in <b>reset</b>
	have been fixed by using the "copy and swap" idiom.
	<li>
	Assertions have been added to check preconditions of various functions;
	however, since these use the new <a href="../../boost/assert.hpp"><boost/assert.hpp></a>
	header, the assertions are disabled by default.
	<li>
	The partial specialization of <b>std::less</b> has been replaced by <b>operator<</b>
	overloads which accomplish the same thing without relying on undefined
	behavior.
	<li>
	The incorrect overload of <b>std::swap</b> has been replaced by <b>boost::swap</b>,
	which has many of the same advantages for generic programming but does not
	violate the C++ standard.</li>
	</ul>
	<hr>
	<p>Revised 1 February 2002</p>
	<p><small>Copyright 2002 Darin Adler. Distributed under the Boost Software License, Version
	1.0. See accompanying file <A href="../../LICENSE_1_0.txt">LICENSE_1_0.txt</A> or
	copy at <A href="http://www.boost.org/LICENSE_1_0.txt">http://www.boost.org/LICENSE_1_0.txt</A>.</small></p>
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