How to randomly select a class to instantiate without using switch?

Question

I\'m refactoring a single 3000+-line class with a tangled web of conditionals and switches into a set of worker classes. Previously part of the constructor would select whic

Answer 1

The answer is : a base class and an array of function pointers can help you do that.

struct Base { virtual ~Base() {} }; //make ~Base() virtual
struct Foo : Base {};
struct Bar : Base {};
struct Baz : Base {};

template
Base *Create() { return new T(); }

typedef Base* (*CreateFn)();

CreateFn create[] = 
         {
              &Create, 
              &Create,   // weighted towards FOO
              &Create, 
              &Create
         }; 
const size_t fncount = sizeof(create)/sizeof(*create);

Base *Create()
{
   return create[rand() % fncount](); //forward the call
}

Then use it as (ideone demo):

int main() {
        Base *obj = Create();
        //work with obj using the common interface in Base

        delete obj; //ok, 
                    //the virtual ~Base() lets you do it 
                    //in a well-defined way
        return 0;
}