Inheriting both an interface and a C ++ implementation

Question

I usually try to find the answers here before posting anything, but I'm not even sure how to formulate my question.

So, here is what I want to do ... I want to define a base interface and a derived interface. Then I want to implement a basic interface with additional variables and methods. Finally, I want to implement the Derived class from an implemented base interface, BUT ALSO from a derived interface. I don’t know about you, but my head hurts.

If I do something like the following, I get Undefined definitions in the DerivedFloat code, because this code “sees” the GetBaseValue method from IBase inherited from IDerivedFloat, as well as GetBaseValue inherited from Base.

Of course, there must be a way to get a class that uses the advanced features of the base implementation, and also make sure that it implements the required IDerivedFloat methods.

Now ... This is a dummy example to show what I'm conceptually trying to achieve. This is not a real life example.

template <typename VALUE_TYPE>
class IBase
{
public:
  virtual VALUE_TYPE GetBaseValue() const = 0;
};

class IDerivedFloat : public IBase<FLOAT>
{
public:
  virtual void SetBaseValue(const FLOAT & value) = 0;
};

// Implementation of Base
template <typename VALUE_TYPE>
class Base : public IBase<VALUE_TYPE>
{
public:
  VALUE_TYPE GetBaseValue() const { return m_BaseValue; }

protected:
  VALUE_TYPE m_BaseValue;
}

// Uses expanded Base AND implements IDerivedFloat
class DerivedFloat : public Base<FLOAT>, public IDerivedFloat
{
public:
   void SetBaseValue(const FLOAT & value) { m_BaseValue = value };
}

Answer 1

You can use virtual inheritance to solve this problem:

class IDerivedFloat : virtual IBase<FLOAT>
{
public:
  virtual void SetBaseValue(const FLOAT & value) = 0;
};

template <typename VALUE_TYPE>
class Base : virtual IBase<VALUE_TYPE>
{
public:
  VALUE_TYPE GetBaseValue() const { return m_BaseValue; }

protected:
  VALUE_TYPE m_BaseValue;
}

Using virtual inheritance, you get one instance of a class of base classes, and not one of them every time it exists in the class hierarchy.

Answer 2

- , , . , , super .

:
- C A B.
- A B add().
- C A:: add() B:: add(), , .

: http://www.cprogramming.com/tutorial/multiple_inheritance.html