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I have another question following on from my previous question about abstractions, I have another problem in relation to setting data at the event once it has been created.

As things stand, I can create events of any type and apply their data no problem (using a modified version of the strategy design pattern). The problem is that I currently have to pass the event its data when it is created.

IEvent* newEvent = new SpeedEvent( eventID, interpolation, 50.0f );

or

IEvent* newEvent = new AnimationEvent( eventID, interpolation, &newAnimation );

This method is fine when I know what the data is at creation of the object, but there are many cases where I won't know what the data will be in instantiation.

What would be ideal, would be to create a new event as such:

IEvent* newEvent = new SpeedEvent( eventID, interpolation );

And then assign it data in this fashion:

eventManager->assignData( eventID, *unknown data type* );

This way, I would let the object handle the data in its own way. Any suggestions as to how to solve this problem would be much appreciated, however I really want to avoid using templates if I can.

My current data and object structure is very similar to the one suggested in the answer to my previous question.

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Agenten
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  • Overload the relevant `Event` type constructor to take two parameters and then create a function `assignData(int Id, Base* data)` in the base that can take any type derived from `Base` – Tony The Lion Feb 27 '13 at 09:18
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    Can't you delay the instantiation enough that all data is available. Moving constructor parameter away simply because someone doesn't have it available yet is not a good plan. It's better to delay the instantiation, and create the object when all data is available. – tp1 Feb 27 '13 at 09:32
  • My plan is to have all new events be given a default value, eg. speed at event is the same as the default one for the animation is it interpolating (this value does exist). What I cant to do is once the event is the created, the user can then update it using the GUI. – Agenten Feb 27 '13 at 11:07

2 Answers2

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You can use Boost.Any to transfer unknown data. On source site you simply use asignment and on the sink site you use any_cast to get recover your value.

Edit a litle code:

simply use boost::any as unknown data type and asign your values (with your concrete type) to it. On the side where you need the concrete type you use any_cast.

class EventManager {
  //...
public:
  void asignData(std::size_t eventId, boost::any value);
  boost::any getData(std::size_t eventId) const;
};

eventManager->assignData( eventId, 12);  // assignes an int
eventManager->assignData( eventId, 12.0);  // assignes an double


int value1=boost::any_cast<int>(eventManager->getData(eventID)); // gets an int
double value2=boost::any_cast<double>(eventManager->getData(eventID)); // gets a double
Jan Herrmann
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  • I really want to avoid using the Boost library if I can, I'm already using Intel Threaded Building Blocks, DirectX 11, Rapid XML and FBX SDK. I don't think my brain can handle another API/SDK! – Agenten Feb 27 '13 at 11:00
  • It's an argument. But most of Boost including Any is header only. Simply unpack it and add it to your include path. As an alternative you can try http://www.boost.org/doc/libs/1_44_0/tools/bcp/doc/html/index.html to extract exacly Boost.Any. – Jan Herrmann Feb 27 '13 at 11:13
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If you have no restrictions on the data, use the good old void * as the data type. Inside the concrete handler cast to the correct type which is known inside the handler.

If you want to pose restrictions on the data, define interface/base that outlines your data specifications and inherit from it for each of the possible concrete data types. Send the data of derived type to your generic handler (that accepts pointer to base class). Inside the handler you can either use the public interface that you defined for the data or simply cast to the concrete type.

SomeWittyUsername
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  • I've actually gone for a system kind of like this. Not using void pointers, but seeing as I store each events as a pointer to its abstract base, I can then use a `dynamic_case<>` to access any mutators I need. – Agenten Feb 28 '13 at 07:52