Talk:Virtual inheritance

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Logical spectrum of article via keyword/keyphrase counts

The article keyword/keyphrase count (and keywords/key phrase) is listed below. Generating a PDF version of the article and doing a search via Adobe PDF reader version 7 is a good way to quickly find the keywords and how they are used in the article

These counts are from the July 26 2006 version of the article.

These counts are useful to content comparison/replication in other articles dealing with object-oriented language inheritance phenomena.

Some of the words below are not keywords/key phrases but are highly relevant to accurate articulation of the subject matter. They are included to help in comparative analysis of other articles.

Running the same pattern over the C++, C# and Java language specification shows the article (WikiPedia VI article) makes very few assumptions when compared to a formal ISO language spec (as it should as a reference document Vs. an architecture/spec doc).

Note the logical spectrum gives an accurate breakdown of what the core focus of the article is. The same table can be resorted (mannually of course) based on highest count first. This is done at the bottom to show the top dozen logical keys in the content.

010 - keyword
042 - phenomena
---------
252 - inheritance
001 - class inheritance phenomena
150 - virtual inheritance
007 - virtual inheritance phenomena
028 - (VI)
---------
011 - general virtual inheritance
015 - (GVI)
009 - simple virtual inheritance
015 - (SVI)
---------
002 - implementation inheritance phenomena
028 - implementation inheritance
010 - (II)
---------
169 - code element
012 - implementation code element
099 - virtual code element
---------
094 - use context
004 - use context aspect
---------
008 - virtual keyword
020 - virtual control mechanism
012 - (VCM)
---------
006 - diamond problem
001 - inherited class ambiguity
005 - (ICA)
001 - method override ambiguity
001 - (MOA)
011 - resolution inheritance
---------
015 - binding
005 - element binding
002 - language binding
---------
007 - coupling
001 - element coupling
002 - language coupling
---------
037 - aspect
006 - control aspect
001 - specification aspect
003 - polymorphic aspect
004 - use context aspect
---------
006 - semantic
011 - semantics
001 - semantic aspect
007 - conceptual semantics
---------
003 - syntax
002 - syntax mechanism
---------
042 - mechanism
001 - resolution mechanism
026 - control mechanism
001 - binding mechanism
004 - specification mechanism
002 - pattern mechanism
---------
071 - pattern
013 - pattern unit
002 - pattern unit mechanism
009 - SPD pattern
002 - functional pattern
001 - design pattern
001 - performance pattern

High count list - first 12 counts

252 - inheritance
169 - code element
150 - virtual inheritance
099 - virtual code element
094 - use context
071 - pattern
042 - phenomena
042 - mechanism
037 - aspect
028 - (VI)
028 - implementation inheritance
026 - control mechanism

—Preceding unsigned comment added by Shawn wiki (talk • contribs) 13:33, 26 July 2006 (UTC)[reply]

"The solution" does not solve the diamond problem

Unless I'm missing something, the solution does not work if both WingedAnimal and Mammal override eat(), as stated in diamond problem. g++ complains as follows:

#include <iostream>

class Animal 
{
	public:
	virtual void eat()
	{
		std::cout << "Animal" << std::endl;
	}
};
 
class Mammal : public virtual Animal 
{
	public:
	virtual void eat()
	{
		std::cout << "Mammal" << std::endl;
	}
};
 
class WingedAnimal : public virtual Animal 
{
	public:
	virtual void eat()
	{
		std::cout << "WingedAnimal" << std::endl;
	}
};
 
// A bat is a winged mammal
class Bat : public WingedAnimal, public Mammal {};

int main()
{
	Bat bat;
	bat.eat();
}

multiple inh.cpp:31: error: no unique final overrider for 'virtual void Animal::eat()' in 'Bat'
multiple inh.cpp: In function 'int main()':
multiple inh.cpp:36: error: request for member 'eat' is ambiguous
multiple inh.cpp:15: error: candidates are: virtual void Mammal::eat()
multiple inh.cpp:24: error:                 virtual void WingedAnimal::eat()

118.7.198.171 (talk) 08:16, 14 June 2009 (UTC)[reply]

You're right, the example is horrible in that it sets up a problem that isn't dealt with/solved by virtual inheritance. I've rewritten a new example which I think more correctly demonstrates the problem that virtual inheritance is designed to fix. --Colonel Cow (talk) 17:03, 8 August 2009 (UTC)[reply]

Hug? Why would you want to do that????

The problem with such Animal hierarchy: one doesn't know what real problem is being solved! WPcorrector (talk) 05:06, 10 November 2011 (UTC)[reply]

problems caused by multiple inheritance?!

I fixed the first paragraph to more exactly explain what virutal inheritance is. It is generally has to do with the inherited incomplete object. The effect on the ambiguity of members is an effect not the source.

Moreover, it is not used to solve any problems caused by multiple inheritance. Multiple inheritance is a language feature that can be used to solve some design problems, it does not and cannot invent design problems. So does virtual inheritance (as a sub-feature of multimple inheritance). It can be said, truely, that abusing a language feature such as multiple inheritance or virtual inheritance (or any other), may result in all sorts of problems (but that a different usage of this word). But that should be put in another article such as Learn design, then learn a programming language, then write code - and not the other way around!. --Itaj Sherman (talk) 15:44, 22 November 2009 (UTC)[reply]

Replicated references

There are two references cited in this article. The first link is supposedly authored by Andrei Milea, while the second is authored by Ralph McArdell. However, both references point to the same URL (specifically the article by Andrei Milea: http://www.cprogramming.com/tutorial/virtual_inheritance.html). Therefore, the second reference is not actually adding anything to the article. —Preceding unsigned comment added by 208.65.73.201 (talk) 18:06, 16 May 2011 (UTC)[reply]

Fixed — Preceding unsigned comment added by 173.196.139.154 (talk) 03:33, 29 December 2012 (UTC)[reply]

"representation" nonsense

The ambiguity is caused by the way C++ implementations typically represent classes. In particular, inheritance is simply a matter of putting parent and child classes one after the other in memory. Thus, Bat is represented as (Animal, Mammal, Animal, WingedAnimal, Bat), which makes Animal duplicated (in other words, Bat owns two different Animal instances, namely a Mammal::Animal and a WingedAnimal::Animal).

Complete non-sense. The ambiguity has nothing to do with representation! Whoever wrote this doesn't understand C++, esp. inheritance, at all and should refrain from writing any article about C++ inheritance.

If you believe that C++ is a "low level language" where the representation of classes is what matters, please actually learn C++ before writing about C++ in WP.

Also please don't complicate this issue even more with slicing, esp. the invocation of implicitly declared copy ctors. WPcorrector (talk) 05:11, 10 November 2011 (UTC)[reply]

Inheritance Order

Virtual inheritance is a C++ technique that ensures only one copy of a base class's member variables are inherited by grandchild derived classes. Without virtual inheritance, if class A is inherits from both classes B and C, and classes B and C both inherit from class D, then class A will contain two copies of D's member variables: one via B, and one via C. These will be accessible independently, using scope resolution.

Instead, if classes B and C inherit virtually from class D, then objects of class A will contain only one set of the member variables from class D.

The order of inheritance doesn't make sense to me. As shown in the UML diagram, D inherits from B and C, B and C inherit from A.--Diaspomod (talk) 11:43, 4 May 2019 (UTC)[reply]

I've tried to fix this. Can you please check? – Tea2min (talk) 19:32, 4 May 2019 (UTC)[reply]