multiple-inheritance

I found this in a website while reading about virtual inheritance in c++ When multiple inheritance is used, it is sometimes necessary to use virtual inheritance. A good example for this is the standard iostream class hierarchy: //Note: this is a simplified description of iostream classes class ostream: virtual public ios { /*..*/ } class istream: virtual public ios { /*..*/ } class iostream : public istream, public ostream { /*..*/ } //a single ios inherited How does C++ ensure that only a single instance of a virtual member exists, regardless of the number of classes derived from it? C++ uses

I know that a class can implement more than one interface, but is it possible to extend more than one class? For example I want my class to extend both TransformGroup and a class I created. Is this possible in Java? Both statements class X extends TransformGroup extends Y and class X extends TransformGroup, Y receive an error. And if it is not possible, why? TransformGroup extends Group but I guess it also extends Node since it inherits fields from Node and it can be passed where a Node object is required. Also, like all classes in Java, they extend Object class. So why wouldn't it be possible

I need a double inheritance for a class. I tried several syntaxes but I don't understand the concept of metaclass. from PyQt5.QtGui import QStandardItem from configparser import ConfigParser class FinalClass(ConfigParser, QStandardItem): def __init__(self, param): ConfigParser.__init__(self) QStandardItem.__init__(self) The problem in your case is that the classes you try to inherit from have different metaclasses: >>> type(QStandardItem) <class 'sip.wrappertype'> >>> type(ConfigParser) <class 'abc.ABCMeta'> Therefore python can't decide which should be the metaclass for the newly created

I got the following class : class ConstraintFailureSet(dict, Exception) : """ Container for constraint failures. It act as a constraint failure itself but can contain other constraint failures that can be accessed with a dict syntax. """ def __init__(self, **failures) : dict.__init__(self, failures) Exception.__init__(self) print isinstance(ConstraintFailureSet(), Exception) True raise ConstraintFailureSet() TypeError: exceptions must be classes, instances, or strings (deprecated), not ConstraintFailureSet What the heck ? And the worst is that I can't try super() since Exception are old based

I need to create a class that uses a different base class depending on some condition. With some classes I get the infamous: TypeError: metaclass conflict: the metaclass of a derived class must be a (non-strict) subclass of the metaclasses of all its bases One example is sqlite3 , here is a short example you can even use in the interpreter: >>> import sqlite3 >>> x = type('x', (sqlite3,), {}) Traceback (most recent call last): File "<stdin>", line 1, in <module> TypeError: metaclass conflict: the metaclass of a derived class must be a (non-strict) subclass of the metaclasses of all its bases

I know virtual inheritance is covered here before and before asking this question I went through the detail of the virtual inheritance and went through the details of a similar problem like the followings: multiple-diamond-inheritance-compiles-without-virtual-but-doesnt-with and why does gcc give me an error - final overrider My problem is slightly different as I am not using pure virtual function and explicitly using virtual inheritance to have one unique 'Base' class. The hierarchy is as follows: Base /\ / \ Der1 Der2 \ / Der3 I know about the dreadful diamond on derivation issue and that's

I have two Java interfaces and one implementing class. (I have used Eclipse to run the program directly, and I did not try to check any compiler warning et cetera by explicitly compiling from the command line.) Why do they run without problem? Why does Java allow this, even when it satisfies the "contract" of both interfaces but create ambiguity in implementing class? Updated the example. public interface CassettePlayer { void play(); } public interface DVDPlayer { void play(); } public class CarPlayer implements CassettePlayer,DVDPlayer{ @Override public void play() { System.out.println("This