Refactoring a leaf class to a base class, and keeping it also a interface implementation
- by elcuco
I am trying to refactor a working code. The code basically derives an interface class into a working implementation, and I want to use this implementation outside the original project as a standalone class.
However, I do not want to create a fork, and I want the original project to be able to take out their implementation, and use mine. The problem is that the hierarchy structure is very different and I am not sure if this would work. I also cannot use the original base class in my project, since in reality it's quite entangled in the project (too many classes, includes) and I need to take care of only a subdomain of the problems the original project is.
I wrote this code to test an idea how to implement this, and while it's working, I am not sure I like it:
#include <iostream>
// Original code is:
// IBase -> Derived1
// I need to refactor Derive2 to be both indipendet class
// and programmers should also be able to use the interface class
// Derived2 -> MyClass + IBase
// MyClass
class IBase {
public:
virtual void printMsg() = 0;
};
///////////////////////////////////////////////////
class Derived1 : public IBase {
public:
virtual void printMsg(){ std::cout << "Hello from Derived 1" << std::endl; }
};
//////////////////////////////////////////////////
class MyClass {
public:
virtual void printMsg(){ std::cout << "Hello from MyClass" << std::endl; }
};
class Derived2: public IBase, public MyClass{
virtual void printMsg(){ MyClass::printMsg(); }
};
class Derived3: public MyClass, public IBase{
virtual void printMsg(){ MyClass::printMsg(); }
};
int main()
{
IBase *o1 = new Derived1();
IBase *o2 = new Derived2();
IBase *o3 = new Derived3();
MyClass *o4 = new MyClass();
o1->printMsg();
o2->printMsg();
o3->printMsg();
o4->printMsg();
return 0;
}
The output is working as expected (tested using gcc and clang, 2 different C++ implementations so I think I am safe here):
[elcuco@pinky ~/src/googlecode/qtedit4/tools/qtsourceview/qate/tests] ./test1
Hello from Derived 1
Hello from MyClass
Hello from MyClass
Hello from MyClass
[elcuco@pinky ~/src/googlecode/qtedit4/tools/qtsourceview/qate/tests] ./test1.clang
Hello from Derived 1
Hello from MyClass
Hello from MyClass
Hello from MyClass
The question is
My original code was:
class Derived3: public MyClass, public IBase{
virtual void IBase::printMsg(){ MyClass::printMsg(); }
};
Which is what I want to express, but this does not compile. I must admit I do not fully understand why this code work, as I expect that the new method Derived3::printMsg() will be an implementation of MyClass::printMsg() and not IBase::printMsg() (even tough this is what I do want).
How does the compiler chooses which method to re-implement, when two "sister classes" have the same virtual function name?
If anyone has a better way of implementing this, I would like to know as well :)
