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<div id="projectbrief">A C++11 library for serialization</div>
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<li class="navelem"><b>cereal</b></li><li class="navelem"><b>memory_detail</b></li><li class="navelem"><a class="el" href="classcereal_1_1memory__detail_1_1EnableSharedStateHelper.html">EnableSharedStateHelper</a></li> </ul>
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<a href="#pub-methods">Public Member Functions</a> |
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<div class="title">cereal::memory_detail::EnableSharedStateHelper< T > Class Template Reference</div> </div>
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<p><code>#include <<a class="el" href="memory_8hpp_source.html">/home/shane/workspace/cereal/include/cereal/types/memory.hpp</a>></code></p>
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<table class="memberdecls">
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<tr class="heading"><td colspan="2"><h2 class="groupheader"><a name="pub-methods"></a>
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Public Member Functions</h2></td></tr>
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<tr class="memitem:a7358952ac850c005295f899a5aa3b184"><td class="memItemLeft" align="right" valign="top"> </td><td class="memItemRight" valign="bottom"><a class="el" href="classcereal_1_1memory__detail_1_1EnableSharedStateHelper.html#a7358952ac850c005295f899a5aa3b184">EnableSharedStateHelper</a> (T *ptr)</td></tr>
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<tr class="memdesc:a7358952ac850c005295f899a5aa3b184"><td class="mdescLeft"> </td><td class="mdescRight">Saves the state of some type inheriting from enable_shared_from_this. <a href="classcereal_1_1memory__detail_1_1EnableSharedStateHelper.html#a7358952ac850c005295f899a5aa3b184">More...</a><br /></td></tr>
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void </td><td class="memItemRight" valign="bottom"><a class="el" href="classcereal_1_1memory__detail_1_1EnableSharedStateHelper.html#ae9cd690a665f3c864b6963f9b69b64cf">restore</a> ()</td></tr>
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<tr class="memdesc:ae9cd690a665f3c864b6963f9b69b64cf"><td class="mdescLeft"> </td><td class="mdescRight">Restores the state of the held pointer (can only be done once) <br /></td></tr>
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<tr class="separator:ae9cd690a665f3c864b6963f9b69b64cf"><td class="memSeparator" colspan="2"> </td></tr>
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 </td><td class="memItemRight" valign="bottom"><a class="el" href="classcereal_1_1memory__detail_1_1EnableSharedStateHelper.html#a33651283607ae0b7cf4eb7918931a98a">~EnableSharedStateHelper</a> ()</td></tr>
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<tr class="memdesc:a33651283607ae0b7cf4eb7918931a98a"><td class="mdescLeft"> </td><td class="mdescRight">Restores the state of the held pointer if not done previously. <br /></td></tr>
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<tr class="separator:a33651283607ae0b7cf4eb7918931a98a"><td class="memSeparator" colspan="2"> </td></tr>
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</table>
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<a name="details" id="details"></a><h2 class="groupheader">Detailed Description</h2>
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<div class="textblock"><h3>template<class T><br />
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class cereal::memory_detail::EnableSharedStateHelper< T ></h3>
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<p>A helper struct for saving and restoring the state of types that derive from std::enable_shared_from_this</p>
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<p>This special struct is necessary because when a user uses load_and_construct, the weak_ptr (or whatever implementation defined variant) that allows enable_shared_from_this to function correctly will not be initialized properly.</p>
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<p>This internal weak_ptr can also be modified by the shared_ptr that is created during the serialization of a polymorphic pointer, where cereal creates a wrapper shared_ptr out of a void pointer to the real data.</p>
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<p>In the case of load_and_construct, this happens because it is the allocation of shared_ptr that perform this initialization, which we let happen on a buffer of memory (aligned_storage). This buffer is then used for placement new later on, effectively overwriting any initialized weak_ptr with a default initialized one, eventually leading to issues when the user calls shared_from_this.</p>
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<p>To get around these issues, we will store the memory for the enable_shared_from_this portion of the class and replace it after whatever happens to modify it (e.g. the user performing construction or the wrapper shared_ptr in saving).</p>
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<p>Note that this goes into undefined behavior territory, but as of the initial writing of this, all standard library implementations of std::enable_shared_from_this are compatible with this memory manipulation. It is entirely possible that this may someday break or may not work with convoluted use cases.</p>
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<p>Example usage:</p>
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<div class="fragment"><div class="line">T * myActualPointer;</div>
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<div class="line">{</div>
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<div class="line"> EnableSharedStateHelper<T> helper( myActualPointer ); <span class="comment">// save the state</span></div>
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<div class="line"> std::shared_ptr<T> myPtr( myActualPointer ); <span class="comment">// modifies the internal weak_ptr</span></div>
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<div class="line"> <span class="comment">// helper restores state when it goes out of scope</span></div>
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<div class="line">}</div>
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</div><!-- fragment --><p>When possible, this is designed to be used in an RAII fashion - it will save state on construction and restore it on destruction. The restore can be done at an earlier time (e.g. after construct() is called in load_and_construct) in which case the destructor will do nothing. Performing the restore immediately following construct() allows a user to call shared_from_this within their load_and_construct function.</p>
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<dl class="tparams"><dt>Template Parameters</dt><dd>
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<table class="tparams">
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<tr><td class="paramname">T</td><td>Type pointed to by shared_ptr </td></tr>
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</table>
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</dd>
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</dl>
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</div><h2 class="groupheader">Constructor & Destructor Documentation</h2>
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<a id="a7358952ac850c005295f899a5aa3b184"></a>
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<h2 class="memtitle"><span class="permalink"><a href="#a7358952ac850c005295f899a5aa3b184">◆ </a></span>EnableSharedStateHelper()</h2>
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template<class T > </div>
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<td class="memname"><a class="el" href="classcereal_1_1memory__detail_1_1EnableSharedStateHelper.html">cereal::memory_detail::EnableSharedStateHelper</a>< T >::<a class="el" href="classcereal_1_1memory__detail_1_1EnableSharedStateHelper.html">EnableSharedStateHelper</a> </td>
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<td>(</td>
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<td class="paramtype">T * </td>
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<td class="paramname"><em>ptr</em></td><td>)</td>
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<td></td>
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<p>Saves the state of some type inheriting from enable_shared_from_this. </p>
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<dl class="params"><dt>Parameters</dt><dd>
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<table class="params">
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<tr><td class="paramname">ptr</td><td>The raw pointer held by the shared_ptr </td></tr>
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</dd>
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</dl>
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</div>
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<hr/>The documentation for this class was generated from the following file:<ul>
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<li><a class="el" href="memory_8hpp_source.html">memory.hpp</a></li>
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