ceph/src/boost/libs/smart_ptr/compatibility.htm

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   8         <h1><img height="86" alt="boost.png (6897 bytes)" src="../../boost.png"
   9             width="277" align="middle" border="0">Smart Pointer Changes</h1>
  10         <p>The February 2002 change to the Boost smart pointers introduced a number of
  11             changes. Since the previous version of the smart pointers was in use for a long
  12             time, it's useful to have a detailed list of what changed from a library user's
  13             point of view.</p>
  14         <p>Note that for compilers that don't support member templates well enough, a
  15             separate implementation is used that lacks many of the new features and is more
  16             like the old version.</p>
  17         <h2>Features Requiring Code Changes to Take Advantage</h2>
  18         <ul>
  19             <li>
  20                 The smart pointer class templates now each have their own header file. For
  21                 compatibility, the <a href="../../boost/smart_ptr.hpp">&lt;boost/smart_ptr.hpp&gt;</a>
  22             header now includes the headers for the four classic smart pointer class
  23             templates.
  24             <li>
  25                 The <b>weak_ptr</b>
  26             template was added.
  27             <li>
  28                 The new <b>shared_ptr</b> and <b>shared_array</b> relax the requirement that
  29                 the pointed-to object's destructor must be visible when instantiating the <b>shared_ptr</b>
  30             destructor. This makes it easier to have shared_ptr members in classes without
  31             explicit destructors.
  32             <li>
  33                 A custom deallocator can be passed in when creating a <b>shared_ptr</b> or <b>shared_array</b>.
  34             <li>
  35                 <b>shared_static_cast</b> and <b>shared_dynamic_cast</b> function templates are
  36                 provided which work for <b>shared_ptr</b> and <b>weak_ptr</b> as <b>static_cast</b>
  37                 and <b>dynamic_cast</b>
  38             do for pointers.
  39             <li>
  40                 The self-assignment misfeature has been removed from <b>shared_ptr::reset</b>,
  41                 although it is still present in <b>scoped_ptr</b>, and in <b>std::auto_ptr</b>.
  42                 Calling <b>reset</b> with a pointer to the object that's already owned by the <b>shared_ptr</b>
  43             results in undefined behavior (an assertion, or eventually a double-delete if
  44             assertions are off).
  45             <li>
  46                 The <b>BOOST_SMART_PTR_CONVERSION</b>
  47             feature has been removed.
  48             <li>
  49                 <b>shared_ptr&lt;void&gt;</b> is now allowed.</li>
  50         </ul>
  51         <h2>Features That Improve Robustness</h2>
  52         <ul>
  53             <li>
  54                 The manipulation of use counts is now <a name="threadsafe">thread safe</a> on
  55                 Windows, Linux, and platforms that support pthreads. See the <a href="../../boost/detail/atomic_count.hpp">
  56                     &lt;boost/detail/atomic_count.hpp&gt;</a>
  57             file for details
  58             <li>
  59                 The new shared_ptr will always delete the object using the pointer it was
  60                 originally constructed with. This prevents subtle problems that could happen if
  61                 the last <b>shared_ptr</b> was a pointer to a sub-object of a class that did
  62                 not have a virtual destructor.</li>
  63         </ul>
  64         <h2>Implementation Details</h2>
  65         <ul>
  66             <li>
  67                 Some bugs in the assignment operator implementations and in <b>reset</b>
  68             have been fixed by using the "copy and swap" idiom.
  69             <li>
  70                 Assertions have been added to check preconditions of various functions;
  71                 however, since these use the new <a href="../../boost/assert.hpp">&lt;boost/assert.hpp&gt;</a>
  72             header, the assertions are disabled by default.
  73             <li>
  74                 The partial specialization of <b>std::less</b> has been replaced by <b>operator&lt;</b>
  75             overloads which accomplish the same thing without relying on undefined
  76             behavior.
  77             <li>
  78                 The incorrect overload of <b>std::swap</b> has been replaced by <b>boost::swap</b>,
  79                 which has many of the same advantages for generic programming but does not
  80                 violate the C++ standard.</li>
  81         </ul>
  82         <hr>
  83         <p>$Date$</p>
  84         <p><small>Copyright 2002 Darin Adler. Distributed under the Boost Software License, Version
  85             1.0. See accompanying file <A href="../../LICENSE_1_0.txt">LICENSE_1_0.txt</A> or
  86             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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