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POUsing a generic method pointer of a base class to call methods of derived classes
 

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    <p>I'm trying to create an event handling system where objects can subscribe to events broadcasted by other objects and call a method when that event is broadcast. I'm trying to implement this with a singleton class called <code>EventHandler</code>. Objects call a public method on <code>EventHandler</code> that subscribes them to events broadcast by a certain object:</p> <pre><code>void startWatchingObjectEvent(PDObject * object, PDEvent event, PDObject* listener, PDReceiver receiver); </code></pre> <p><code>PDObject</code> is a base class for all the objects that will be handled by the <code>EventHandler</code>. <code>PDEvent</code> is simply a unique string that identifies the Event. </p> <p><code>PDReceiver</code> is where I'm running into issues. I have it typedef'd to a method pointer on the <code>PDObject</code> class:</p> <pre><code>typedef void (PDObject::*PDReceiver)(PDObject*, PDEvent); </code></pre> <p>Now the <code>PDObject</code> class itself doesn't really have any methods that <code>EventHandler</code> is going to call, but derived classes of <code>PDObject</code> will, and I wanted to create a generic type that <code>EventHandler</code> could store that would apply to any derived classes of <code>PDObject</code>. I implemented <code>EventHandler</code> this way and tried writing a unit test to make sure it's working okay:</p> <pre><code>const PDEvent Test_PokeEvent = "Test_PokeEvent"; void Test_EventHandler_sendObjectMessage() { EventHandler&amp; eventh = EventHandler::instance(); Test_PDObject caster; Test_PDObject listener; PDReceiver receiver = &amp;Test_PDObject::test_poke; eventh.startWatchingObjectEvent(&amp;caster, Test_PokeEvent, &amp;listener, (listener.*receiver)(&amp;caster, Test_PokeEvent)); eventh.sendObjectEvent(&amp;caster, Test_PokeEvent); assert(listener.test_wasPoked()); } </code></pre> <p><code>Test_PDObject</code> is a derived class of <code>PDObject</code> that just flips a <code>wasPoked</code> bit when <code>test_poke</code> is called.</p> <p>The issue is that the compiler doesn't like me trying to assign a method of <code>Test_PDObject</code> to the type <code>PDReceiver</code> since <code>PDReceiver</code> is defined as a method of <code>PDObject</code>.</p> <p>Is what I'm trying to do even possible? Can I use this generic method pointer type to refer to methods of derived classes? Or is my approach just entirely flawed?</p> <p>EDIT: I figured out I can use <code>static_cast</code> to cast the method pointer of the derived class to a method pointer of the base class like so:</p> <pre><code>PDReceiver receiver = static_cast&lt;PDReceiver&gt;(&amp;Test_PDObject::test_poke); </code></pre> <p>And so far so good! My unit tests are working perfectly now.</p>
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    1. COYou should not update the question with the answer, but instead either mark one of the posted answers as *accepted*, or answer your own question and mark that post as *accepted*.
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      1. USFilip Roséen - refp
    2. COOkay. I'm new here, so thanks for letting me know. :)
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