| 1 | <!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN"> |
|---|
| 2 | |
|---|
| 3 | <html> |
|---|
| 4 | |
|---|
| 5 | <head> |
|---|
| 6 | <meta http-equiv="Content-Type" content="text/html; charset=iso-8859-1"> |
|---|
| 7 | <title>Smart Pointer Changes</title> |
|---|
| 8 | </head> |
|---|
| 9 | |
|---|
| 10 | <body bgcolor="#FFFFFF" text="#000000"> |
|---|
| 11 | |
|---|
| 12 | <h1><img src="../../boost.png" alt="boost.png (6897 bytes)" align="middle" width="277" height="86">Smart |
|---|
| 13 | Pointer Changes</h1> |
|---|
| 14 | |
|---|
| 15 | <p>The February 2002 change to the Boost smart pointers introduced a number |
|---|
| 16 | of changes. Since the previous version of the smart pointers was in use for |
|---|
| 17 | a long time, it's useful to have a detailed list of what changed from a library |
|---|
| 18 | user's point of view.</p> |
|---|
| 19 | |
|---|
| 20 | <p>Note that for compilers that don't support member templates well enough, |
|---|
| 21 | a separate implementation is used that lacks many of the new features and is |
|---|
| 22 | more like the old version.</p> |
|---|
| 23 | |
|---|
| 24 | <h2>Features Requiring Code Changes to Take Advantage</h2> |
|---|
| 25 | |
|---|
| 26 | <ul> |
|---|
| 27 | |
|---|
| 28 | <li>The smart pointer class templates now each have their own header file. |
|---|
| 29 | For compatibility, the |
|---|
| 30 | <a href="../../boost/smart_ptr.hpp"><boost/smart_ptr.hpp></a> |
|---|
| 31 | header now includes the headers for the four classic smart pointer class templates.</li> |
|---|
| 32 | |
|---|
| 33 | <li>The <b>weak_ptr</b> template was added.</li> |
|---|
| 34 | |
|---|
| 35 | <li>The new <b>shared_ptr</b> and <b>shared_array</b> relax the requirement that the pointed-to object's |
|---|
| 36 | destructor must be visible when instantiating the <b>shared_ptr</b> destructor. |
|---|
| 37 | This makes it easier to have shared_ptr members in classes without explicit destructors.</li> |
|---|
| 38 | |
|---|
| 39 | <li>A custom deallocator can be passed in when creating a <b>shared_ptr</b> or <b>shared_array</b>.</li> |
|---|
| 40 | |
|---|
| 41 | <li><b>shared_static_cast</b> and <b>shared_dynamic_cast</b> function templates are |
|---|
| 42 | provided which work for <b>shared_ptr</b> and <b>weak_ptr</b> as <b>static_cast</b> and |
|---|
| 43 | <b>dynamic_cast</b> do for pointers.</li> |
|---|
| 44 | |
|---|
| 45 | <li>The self-assignment misfeature has been removed from <b>shared_ptr::reset</b>, |
|---|
| 46 | although it is still present in <b>scoped_ptr</b>, and in <b>std::auto_ptr</b>. |
|---|
| 47 | Calling <b>reset</b> with a pointer to the object that's already owned by the |
|---|
| 48 | <b>shared_ptr</b> results in undefined behavior |
|---|
| 49 | (an assertion, or eventually a double-delete if assertions are off).</li> |
|---|
| 50 | |
|---|
| 51 | <li>The <b>BOOST_SMART_PTR_CONVERSION</b> feature has been removed.</li> |
|---|
| 52 | |
|---|
| 53 | <li><b>shared_ptr<void></b> is now allowed.</li> |
|---|
| 54 | |
|---|
| 55 | </ul> |
|---|
| 56 | |
|---|
| 57 | <h2>Features That Improve Robustness</h2> |
|---|
| 58 | |
|---|
| 59 | <ul> |
|---|
| 60 | |
|---|
| 61 | <li>The manipulation of use counts is now <a name="threadsafe">thread safe</a> on Windows, Linux, and platforms |
|---|
| 62 | that support pthreads. See the |
|---|
| 63 | <a href="../../boost/detail/atomic_count.hpp"><boost/detail/atomic_count.hpp></a> |
|---|
| 64 | file for details</li> |
|---|
| 65 | |
|---|
| 66 | <li>The new shared_ptr will always delete the object using the pointer it was originally constructed with. |
|---|
| 67 | This prevents subtle problems that could happen if the last <b>shared_ptr</b> was a pointer to a sub-object |
|---|
| 68 | of a class that did not have a virtual destructor.</li> |
|---|
| 69 | |
|---|
| 70 | </ul> |
|---|
| 71 | |
|---|
| 72 | <h2>Implementation Details</h2> |
|---|
| 73 | |
|---|
| 74 | <ul> |
|---|
| 75 | |
|---|
| 76 | <li>Some bugs in the assignment operator implementations and in <b>reset</b> |
|---|
| 77 | have been fixed by using the "copy and swap" idiom.</li> |
|---|
| 78 | |
|---|
| 79 | <li>Assertions have been added to check preconditions of various functions; |
|---|
| 80 | however, since these use the new |
|---|
| 81 | <a href="../../boost/assert.hpp"><boost/assert.hpp></a> |
|---|
| 82 | header, the assertions are disabled by default.</li> |
|---|
| 83 | |
|---|
| 84 | <li>The partial specialization of <b>std::less</b> has been replaced by <b>operator<</b> |
|---|
| 85 | overloads which accomplish the same thing without relying on undefined behavior.</li> |
|---|
| 86 | |
|---|
| 87 | <li>The incorrect overload of <b>std::swap</b> has been replaced by <b>boost::swap</b>, which |
|---|
| 88 | has many of the same advantages for generic programming but does not violate the C++ standard.</li> |
|---|
| 89 | |
|---|
| 90 | </ul> |
|---|
| 91 | |
|---|
| 92 | <hr> |
|---|
| 93 | |
|---|
| 94 | <p>Revised 1 February 2002</p> |
|---|
| 95 | |
|---|
| 96 | <p>Copyright 2002 Darin Adler. |
|---|
| 97 | Permission to copy, use, |
|---|
| 98 | modify, sell and distribute this document is granted provided this copyright |
|---|
| 99 | notice appears in all copies. This document is provided "as is" |
|---|
| 100 | without express or implied warranty, and with no claim as to its suitability for |
|---|
| 101 | any purpose.</p> |
|---|
| 102 | |
|---|
| 103 | </body> |
|---|
| 104 | |
|---|
| 105 | </html> |
|---|
