Every class without an explicit superclass inherits from java.lang.Object and every other class inherits from it indirectly because when you go up the inheritance tree, you will finally end at a class without an explicit superclass and then at Object. java.lang.Class is the superclass of all class objects (not of all objects!), for example of … Read more
Delphi does not support Multiple Inheritance. But classes can support / implement multiple interfaces and you can delegate interface implementation, so you can kinda simulate multiple inheritence.
It looks like you want to do virtual inheritance. Whether that turns out to actually be a good idea is another question, but here’s how you do it: class AbsBase {…}; class AbsInit: public virtual AbsBase {…}; class AbsWork: public virtual AbsBase {…}; class NotAbsTotal: public AbsInit, public AbsWork {…}; Basically, the default, non-virtual multiple … Read more
The error message indicates that you have two conflicting metaclasses somewhere in your hierarchy. You need to examine each of your classes and the QT classes to figure out where the conflict is. Here’s some simple example code that sets up the same situation: class MetaA(type): pass class MetaB(type): pass class A: __metaclass__ = MetaA … Read more
The memory layout and the vtable layout depend on your compiler. Using my gcc for instance, they look like this: sizeof(int) == 4 sizeof(A) == 8 sizeof(B) == 8 sizeof(C) == 20 Note that sizeof(int) and the space needed for the vtable pointer can also vary from compiler to compiler and platform to platform. The … Read more
does pa point to a valid A object? does pb point to a valid B object? Yes, the C* gets converted so that pa and pb point to the correct addresses. does pa == pb ? No, usually not. There can’t be an A object and a B object at the same address. Furthermore, does … Read more
Inheritance is the second strongest (more coupling) relations in C++, preceded only by friendship. If you can redesign into using only composition your code will be more loosely coupled. If you cannot, then you should consider whether all your classes should really inherit from the base. Is it due to implementation or just an interface? … Read more
Actually, I have no good answer other than Java SHOULD have Multiple Inheritance. The whole point that interfaces should be able to replace the need for Multiple Inheritance is like the big lie that when repeated enough times becomes true. The argument is that Multiple Inheritance causes all these problems (la-di-dah), yet I keep hearing … Read more
A function overrides a virtual function of a base class based on the name and parameter types (see below). Therefore, your class C has two virtual functions foo, one inherited from each A and B. But a function void C::foo() overrides both: [class.virtual]/2 If a virtual member function vf is declared in a class Base … Read more
This has nothing to do with overriding functions. It has to do with conversions. It really doesn’t have to do with accessibility (i.e “private” or such) directly either. Here is a simpler example struct A { int a; }; struct B : A { }; struct C : B, A { }; // direct A … Read more