Other Inheritance Issues

Notes

• class DerivedIdT: [access-specifier] BaseIdT
  • if the access-specifier is missing, the access is public
• Private inheritance
  • All public and protected members of the base class are now private members of the derived class.
  • This is useful at a higher level design concepts
  • One of these is composition.
  • But Gregorie suggests that this might not be well known, so advises against it.
  • I would avoid it until you become more skilled at inheritance.
• Protected is very strange
  • All public and protected members of the base become protected in the derived class.
  • Very few places give concrete reasons for this.
  • I would avoid it until you become more skilled at inheritance.
• Virtual
  • class DerivedIdT : virtual public BaseIdT {
    • We will explore this later
    • But it marks the base class as virtual.
    • And the most derived object contains only one instance of this base class.
  • This is used in multiple inheritance as a solution to the diamond problem.
• Multiple Inheritance
  • class DerivedIdT: public BaseA, public BaseB, ...{
  • The derived class will inherit from all listed classes.
  • This is not bad, unless any ancestor is shared, then we have the diamond problem.
• The diamond problem
  • We have a PlayerT
  • From that is derived a FighterT and a WizardT
    • Both have the members of the base class.
  • From both of these classes we derive the FighterWizardT
    • Unless the base classes are marked virtual, the FighterWizardT will contain two copies of the PlayerT members.
  • This will lead to all kinds of ambiguities when trying to build the code because of multiple versions of base class member functions.
  • And it will cause problems with multiple different versions of base class member variables, with multiple different values.
  • See diamond1.cpp and diamond2.cpp.