I worked on an aircraft simulation once, that had what they (somewhat confusingly) referred to as a "Simulation Database". You could register variables like floats or ints or strings in it, and people could search for them by name, and pull out a reference to them. You could also register a model (an object of a class descended from "SimModel"). The way I used RTTI, was to make it so you could search for models that implement a given interface:
SimModel* SimDatabase::FindModel<type*>(char* name="")
{
foreach(SimModel* mo in ModelList)
if(name == "" || mo->name eq name)
{
if(dynamic_cast<type*>mo != NULL)
{
return dynamic_cast<type*>mo;
}
}
return NULL;
}
The SimModel base class:
class public SimModel
{
public:
void RunModel()=0;
};
An example interface might be "EngineModel":
class EngineModelInterface : public SimModel
{
public:
float RPM()=0;
float FuelFlow()=0;
void SetThrottle(float setting)=0;
};
Now, to make a Lycoming and Continental engine:
class LycomingIO540 : public EngineModelInterface
{
public:
float RPM()
{
return rpm;
}
float FuelFlow()
{
return throttleSetting * 10.0;
}
void SetThrottle(float setting)
{
throttleSetting = setting
}
void RunModel() // from SimModel base class
{
if(throttleSetting > 0.5)
rpm += 1;
else
rpm -= 1;
}
private:
float rpm, throttleSetting;
};
class Continental350: public EngineModelInterface
{
public:
float RPM()
{
return rand();
}
float FuelFlow()
{
return rand;
}
void SetThrottle(float setting)
{
}
void RunModel() // from SimModel base class
{
}
};
Now, here's some code where somebody wants an engine:
.
.
EngineModelInterface * eng = simDB.FindModel<EngineModelInterface *>();
.
.
fuel = fuel - deltaTime * eng->FuelFlow();
.
.
.
Code is pretty pseudo, but I hope it gets the idea across. One developer can write code that depends on having an Engine, but as long as it has something that implements the engine interface, it doesn't care what it is. So the code that updates the amount of fuel in the tanks is completely decoupled from everything except the FindModel<>() function, and the pure virtual EngineModel interface that he's interested in using. Somebody a year later can make a new engine model, register it with the SimulationDatabase, and the guy above who updates fuel will start using it automatically. I actually made it so you could load new models as plugins (DLLs) at runtime, and once they are registered in the SimulationDatabase, they could be found with FindModel<>(), even though the code that was looking for them was compiled and built into a DLL months before the new DLL existed. You could also add new Interfaces that derive from SimModel, with something that implements them in one DLL, something that searches for them in another DLL, and once you load both DLLs, one can do a FindModel<>() to get the model in the other. Even though the Interface itself didn't even exist when the main app was built.
Parenthetically, RTTI doesn't always work across DLL boundaries. Since I was using Qt anyway, I used qobject_cast instead of dynamic_cast. Every class had to inherit from QObject (and get moc'd), but the qobject meta-data was always available. If you don't care about DLLs, or you are using a toolchain where RTTI does work across DLL boundaries (type comparisons based on string comparisons instead of hashes or whatever), then all of the above with dynamic_cast will work just fine.
