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<div class="textblock"><p>Within the current C++ standard it is not possible to extract a class hierarchy automatically from a certain type. Therefore the programmer has to put a certain macro inside every class in order to provide this information. Additionally this macro will be needed to retrieve the information about the most derived <a class="el" href="classrttr_1_1type.html">type</a> of a current instance.</p>
<p>The macro you have to insert in the class declaration is named: <a class="el" href="rttr__enable_8h.html#a848bcae21d3a54e07ca6450689820a59">RTTR_ENABLE()</a></p>
<p>Suppose we have a base struct called <code>Base</code>: </p><div class="fragment"><div class="line"><span class="keyword">struct </span>Base</div><div class="line">{</div><div class="line"> <a class="code" href="rttr__enable_8h.html#a848bcae21d3a54e07ca6450689820a59">RTTR_ENABLE</a>()</div><div class="line">};</div></div><!-- fragment --><p> Place the macro <a class="el" href="rttr__enable_8h.html#a848bcae21d3a54e07ca6450689820a59">RTTR_ENABLE()</a> somewhere in the class, it doesn't matter if its under the public, protected or private class accessor section.</p>
<p>Into the derived class you put the same macro, but now as argument the name of the parent class. Which is in this case <code>Base</code>. </p><div class="fragment"><div class="line"><span class="keyword">struct </span>Derived : Base</div><div class="line">{</div><div class="line"> <a class="code" href="rttr__enable_8h.html#a848bcae21d3a54e07ca6450689820a59">RTTR_ENABLE</a>(Base)</div><div class="line">};</div></div><!-- fragment --><p>When you use multiple inheritance you simply separate every class with a comma. </p><div class="fragment"><div class="line"><span class="keyword">struct </span>MultipleDerived : Base, Other</div><div class="line">{</div><div class="line"> <a class="code" href="rttr__enable_8h.html#a848bcae21d3a54e07ca6450689820a59">RTTR_ENABLE</a>(Base, Other)</div><div class="line">};</div></div><!-- fragment --><p> Remark that the order in which you declare here the multiple inheritance, has an impact later when retrieving properties of a class. So it is best practice to use the same order like in your class. RTTR supports to register even virtual base classes. </p><dl class="section remark"><dt>Remarks</dt><dd>The only limitation you have is: It is <b>not</b> possible to register a class twice in the same class hierarchy.</dd></dl>
<p>When no class hierarchies are used at all, it is <b>not necessary</b> to use the macro. However it is best practice to place it inside every class. This macro will also enable the possible usage of an own cast operator called: <code>rttr_cast</code>. How this will be done, is discussed in the <a class="el" href="rttr_type_rttr_cast_page.html">next</a> chapter.</p>
<h2>Summary </h2>
<ul>
<li>to retrieve meta information of derived and base classes or using <a class="el" href="namespacerttr.html#ab3dd8b62e5ddca4c1d57cc572ba6bb81">rttr_cast</a>, it is necessary to place the macro: <a class="el" href="rttr__enable_8h.html#a848bcae21d3a54e07ca6450689820a59">RTTR_ENABLE()</a> inside every class declaration</li>
<li>the macro is <b>not</b> needed when working with classes which will be not inherited, e.g. POD classes</li>
</ul>
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