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- <body>
- <div class="document" id="boost-pointer-container-library">
- <h1 class="title"><img alt="Boost" src="boost.png" /> Pointer Container Library</h1>
- <h2 class="subtitle" id="compatible-smart-pointer-type">Compatible Smart Pointer Type</h2>
- <p>When specifying parameter or return types in interfaces, the documentation
- for this library uses the pseudo-type</p>
- <pre class="literal-block">
- <em>compatible-smart-ptr</em><T>
- </pre>
- <p>to indicate that the compiler C++ standard is being used to
- selectively provide or remove interfaces with <tt class="docutils literal"><span class="pre">std::auto_ptr<T></span></tt> or
- <tt class="docutils literal"><span class="pre">std::unique_ptr<T></span></tt>. The exact meaning varies depending on whether
- the smart pointer type is a parameter or a return type.</p>
- <p><strong>Parameter Types:</strong></p>
- <p>An interface such as</p>
- <pre class="literal-block">
- void container::push_back( <em>compatible-smart-ptr</em><T> );
- </pre>
- <p>indicates that an overload of <tt class="docutils literal"><span class="pre">container::push_back</span></tt> is present for
- one or both of <tt class="docutils literal"><span class="pre">std::auto_ptr<T></span></tt>, <tt class="docutils literal"><span class="pre">std::unique_ptr<T></span></tt>;
- Boost.Pointer Container provides an overload for each type supported
- by the compiler. To be completely explicit, if the compiler provides
- <tt class="docutils literal"><span class="pre">std::auto_ptr</span></tt>, then</p>
- <pre class="literal-block">
- void container::push_back( std::auto_ptr<T> );
- </pre>
- <p>is present. If the compiler provides <tt class="docutils literal"><span class="pre">std::unique_ptr</span></tt>, then</p>
- <pre class="literal-block">
- void container::push_back( std::unique_ptr<T> );
- </pre>
- <p>is present. And if the compiler provides both, both overloads are
- present.</p>
- <p>In practice this means that C++98/03 users have access to
- <tt class="docutils literal"><span class="pre">std::auto_ptr</span></tt> overloads, C++11/14 users have access to
- overloads taking both <tt class="docutils literal"><span class="pre">std::auto_ptr</span></tt> and <tt class="docutils literal"><span class="pre">std::unique_ptr</span></tt>, and
- users of C++17 and onwards only have access to <tt class="docutils literal"><span class="pre">std::unique_ptr</span></tt>
- overloads.</p>
- <p>The convention outlined above implies that in certain cases the
- documentation will make reference to a single function taking the
- compatible smart pointer pseudo parameter, when in fact two distinct
- overloaded functions are present. Of course the actual interface
- depends on compiler settings, so for clarity the <a class="reference external" href="reversible_ptr_container.html">class hierarchy
- reference</a> will only ever refer to a
- single function.</p>
- <p><strong>Return Types:</strong></p>
- <p>The case of return types is handled along the same lines as parameter
- types, subject of course to the restriction that C++ functions cannot
- be overloaded by return type. Thus, an interface such as</p>
- <pre class="literal-block">
- <em>compatible-smart-ptr</em><T> container::release( );
- </pre>
- <p>means that precisely one of <tt class="docutils literal"><span class="pre">std::auto_ptr<T></span></tt> or
- <tt class="docutils literal"><span class="pre">std::unique_ptr<T></span></tt> is used as the return type. If the compiler
- provides <tt class="docutils literal"><span class="pre">std::auto_ptr<T></span></tt>, then</p>
- <pre class="literal-block">
- std::auto_ptr<T> container::release( );
- </pre>
- <p>is present, even if the compiler provides <tt class="docutils literal"><span class="pre">std::unique_ptr</span></tt>. For
- compilers that only provide <tt class="docutils literal"><span class="pre">std::unique_ptr</span></tt>, the interface above
- becomes</p>
- <pre class="literal-block">
- std::unique_ptr<T> container::release( );
- </pre>
- <p>In practice, this means that for users of C++98/03/11/14, such return
- types are always <tt class="docutils literal"><span class="pre">std::auto_ptr</span></tt>; for users of C++17 and onwards the
- return type is <tt class="docutils literal"><span class="pre">std::unique_ptr</span></tt>.</p>
- <p><strong>Details:</strong></p>
- <p>The ISO C++11 standard saw the addition of the smart pointer class template
- <tt class="docutils literal"><span class="pre">std::unique_ptr</span></tt>, and with it the formal deprecation of
- <tt class="docutils literal"><span class="pre">std::auto_ptr</span></tt>. After spending C++11 and C++14 with deprecated
- status, <tt class="docutils literal"><span class="pre">std::auto_ptr</span></tt> has been formally removed as of
- the ISO C++17 standard. As such, headers mentioning
- <tt class="docutils literal"><span class="pre">std::auto_ptr</span></tt> may be unusable in standard library
- implementations which disable <tt class="docutils literal"><span class="pre">std::auto_ptr</span></tt> when C++17 or later
- is used. Boost.Pointer Container predates the existence of
- <tt class="docutils literal"><span class="pre">std::unique_ptr</span></tt>, and since Boost v. <tt class="docutils literal">1.34</tt> it has provided
- <tt class="docutils literal"><span class="pre">std::auto_ptr</span></tt> overloads for its interfaces. To provide
- compatibility across a range of C++ standards, macros are used for
- compile-time overloading or replacement of <tt class="docutils literal"><span class="pre">std::auto_ptr</span></tt> interfaces with
- <tt class="docutils literal"><span class="pre">std::unique_ptr</span></tt> interfaces.</p>
- <p><a class="reference external" href="../../config/index.html">Boost.Config</a> defines the macro
- <tt class="docutils literal">BOOST_NO_CXX11_SMART_PTR</tt> for compilers where
- <tt class="docutils literal"><span class="pre">std::unique_ptr</span></tt> is not available, and <tt class="docutils literal">BOOST_NO_AUTO_PTR</tt> for
- compilers where <tt class="docutils literal"><span class="pre">std::auto_ptr</span></tt> is removed (or is defective). These
- macros are used for compile-time selection of interfaces depending on
- parameter and return type. For interfaces that take smart pointer
- parameters, Boost.Pointer Container uses <tt class="docutils literal">BOOST_NO_AUTO_PTR</tt> and
- <tt class="docutils literal">BOOST_NO_CXX11_SMART_PTR</tt> independently of each other to provide
- interfaces taking one or both of <tt class="docutils literal"><span class="pre">std::auto_ptr</span></tt>,
- <tt class="docutils literal"><span class="pre">std::unique_ptr</span></tt> as parameters. For interfaces with smart pointer
- return types, the Boost.Config macros are used first to check if
- <tt class="docutils literal"><span class="pre">std::auto_ptr</span></tt> is available, providing <tt class="docutils literal"><span class="pre">std::unique_ptr</span></tt> as the
- return type only for compilers that provide <tt class="docutils literal"><span class="pre">std::unique_ptr</span></tt> but
- not <tt class="docutils literal"><span class="pre">std::auto_ptr</span></tt>.</p>
- <p>Thus, all mentions of</p>
- <pre class="literal-block">
- <em>compatible-smart-ptr</em><T>
- </pre>
- <p>shall be understood to mean that <a class="reference external" href="../../config/index.html">Boost.Config</a> has been used as outlined above to provide
- a smart pointer interface that is compatible with compiler settings.</p>
- <p><strong>Navigate</strong></p>
- <ul class="simple">
- <li><a class="reference external" href="ptr_container.html">home</a></li>
- <li><a class="reference external" href="reference.html">reference</a></li>
- </ul>
- <hr><table class="docutils field-list" frame="void" rules="none">
- <col class="field-name" />
- <col class="field-body" />
- <tbody valign="top">
- <tr class="field"><th class="field-name">Copyright:</th><td class="field-body">Thorsten Ottosen 2004-2006. Use, modification and distribution is subject to the Boost Software License, Version 1.0 (see <a class="reference external" href="http://www.boost.org/LICENSE_1_0.txt">LICENSE_1_0.txt</a>).</td>
- </tr>
- </tbody>
- </table>
- </div>
- </body>
- </html>
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