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POHow I do define a class method that accepts a derived class member function pointer as a parameter in C++?
 

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  1. POHow I do define a class method that accepts a derived class member function pointer as a parameter in C++?
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    <p>I'm using a Signal-Slot C++ implementation found here: <a href="https://github.com/pbhogan/Signals" rel="nofollow">https://github.com/pbhogan/Signals</a> to implement event listeners within a user interface library I'm developing.</p> <p>The user-facing API goes like so:</p> <pre><code>class DialEventListener : public EventListener { void handleEvent(Event event){ … cout &lt;&lt; "Event on" &lt;&lt; event.source.name &lt;&lt; end; } } int main(){ Interactor dial1; dial1.addListener(ROTATE_EVENT, DialEventListener()); … } </code></pre> <p>To define an event listener, a user would subclass <code>EventListener</code> to create a custom event handler. But in the implementation of <code>Interactor::addListener()</code> where I use the Signals.h code you have to provide a member function pointer as well as a class instance pointer to connect a Delegate to some Signal.</p> <p>Below is an code snippet showing how I'm trying to use Signals to implement event listeners. I use a map from <code>EventType</code>s to <code>Signal</code> to account for an interactor that triggers multiple types of events.</p> <pre><code>typedef map&lt; EventType, Signal1&lt;Event&gt; &gt; EventTypeListenerMap; class Interactor { private: EventTypeListenerMap listener_map; public: void TriggerEvent(Event e){ Signal1&lt;Event&gt; signal = listener_map[e.type]; signal(e); } void addListener(EventType e_type, EventListener listener){ … //Find the signal for a particular kind of event. Signal1&lt;TUIKitEvent&gt; signal = listener_map[e_type]; //Plug a delegate into that signal's slot signal.Connect( &amp;listener, &amp;EventListener::handleEvent); } void addListener(EventType e_type, EventListener listener, void (EventListener::*handler)(Event)){ … Signal1&lt;TUIKitEvent&gt; signal = listener_map[e_type]; signal.Connect( &amp;listener, handler); } } class EventListener { virtual void handleEvent(Event event){ } } </code></pre> <p>The fact that I'm using a Signal-Slot implementation should be hidden from the user, so I just wrote this version of <code>Interactor::addListener(EventType, EventListener, void (EventListener::*))</code> as a sanity check to make sure I was passing the right member function pointer to be bound to that signal. But member function pointers are class specific, so how can one define a function with a signatures that accepts pointers to methods of classes derived from EventListener, which likely don't yet exist?</p>
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    1. UScorntoole
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    1. COI don't think that the question is really clear... why do you want to pass a member function pointer to a derived method and not just a member function to the base type and have the dynamic dispatch resolve the final overrider for you? Maybe you should add a small piece of code pointing out what the user code looks like and the behavior you want from it...
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      1. USDavid Rodríguez - dribeas
 

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