How to Elegantly convert switch+enum with polymorphism
- by Kyle
I'm trying to replace simple enums with type classes.. that is, one class derived from a base for each type. So for example instead of:
enum E_BASE { EB_ALPHA, EB_BRAVO };
E_BASE message = someMessage();
switch (message)
{
case EB_ALPHA: applyAlpha();
case EB_BRAVO: applyBravo();
}
I want to do this:
Base* message = someMessage();
message->apply(this); // use polymorphism to determine what function to call.
I have seen many ways to do this which all seem less elegant even then the basic switch statement. Using dyanimc_pointer_cast, inheriting from a messageHandler class that needs to be updated every time a new message is added, using a container of function pointers, all seem to defeat the purpose of making code easier to maintain by replacing switches with polymorphism.
This is as close as I can get: (I use templates to avoid inheriting from an all-knowing handler interface)
class Base
{
public:
template<typename T> virtual void apply(T* sandbox) = 0;
};
class Alpha : public Base
{
public:
template<typename T> virtual void apply(T* sandbox)
{
sandbox->applyAlpha();
}
};
class Bravo : public Base
{
public:
template<typename T> virtual void apply(T* sandbox)
{
sandbox->applyBravo();
}
};
class Sandbox
{
public:
void run()
{
Base* alpha = new Alpha;
Base* bravo = new Bravo;
alpha->apply(this);
bravo->apply(this);
delete alpha;
delete bravo;
}
void applyAlpha() {
// cout << "Applying alpha\n";
}
void applyBravo() {
// cout << "Applying bravo\n";
}
};
Obviously, this doesn't compile but I'm hoping it gets my problem accross.
