Does C# support multiple inheritance 4.0?

Question

I recently took a practice C# skills test and one of the questions was,

Does C# support multiple inheritance?

I answered yes, and was was marked wrong. After some research online, its full of answers of why it is not supported:

Why is Multiple Inheritance not allowed in Java or C#?

http://www.codeproject.com/Questions/652495/Why-does-csharp-doesnt-support-Multiple-inheritanc

Then I went and tried to replicate the error I should be getting when trying to inherit from a Class that already inherited from a Base Class, and there is no error. I am using console application, and I recently upgraded to .net 4.5, maybe things have changed?

Code for how I tested:

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Collections;

namespace ConsoleApplication2
{
    class Program
    {
        static void Main(string[] args)
        {

            Leo bk = new Leo();

            bk.avgWords();

            Console.ReadLine();

        }

        public void bubbleSort(int[] input)
        {

        }

        public void insertionSort(int[] input)
        {

        }
    }

    public class Gatsby : Books
    {


        public override void avgWords()
        {

            Console.WriteLine(5);

        }

    }

    public class Leo : Gatsby
    {


        public override void avgWords()
        {
            Console.WriteLine(7);
        }

    }

    public class Dicaprio : Leo
    {


    }

    public class Books
    {

        public int id { get; set; }
        public string title { get; set; }
        public string author { get; set; }

        public virtual void avgWords()
        {


            Console.WriteLine(3);
        }


    }
}

That's not what multiple inheritance means. – SLaks Feb 12 '14 at 01:23 — SLaks, Feb 12 '14 at 01:23
This is Multi-level inheritance, not Multiple inheritance. – MVarman Feb 12 '14 at 11:56 — MVarman, Feb 12 '14 at 11:56

score 10 · Answer 1 · answered Feb 12 '14 at 01:22

Then I went and tried to replicate the error I should be getting when trying to inherit from a Class that already inherited from a Base Class, and there is no error. I am using console application, and I recently upgraded to .net 4.5, maybe things have changed?

No, that is still considered single inheritance. Your class only inherits from a single base class.

Some languages, like C++, allow you to inherit from more than one class. The C# version would be something like:

class Foo {} 
class Bar {}

// This is invalid in C#!
class Baz : Foo, Bar {}

However, that's not allowed.

Note that C# does allow you to implement multiple interfaces, however.

score 5 · Answer 2 · answered Feb 12 '14 at 01:34

Does C# support multiple inheritance?

You cannot inherit from multiple base classes, but as with COM, you can re-use multiple base classes through multiple interfaces and containment and delegation:

// class C1 implements interface I1
interface I1
{
    void M1();
}

class C1 : I1
{
    public void M1() { Console.WriteLine("C1.M1"); }
}

// class C2 implements interface I2
interface I2
{
    void M2();
}

class C2 : I2
{
    public void M2() { Console.WriteLine("C2.M2"); }
}

// class C reuses C1 and C2
// it implements I1 and I2 and delegates them accordingly
class C: I1, I2
{
    C1 c1;
    C2 c2;

    void I1.M1() { c1.M1(); }

    void I2.M2() { c2.M2(); }
}

score 3 · Accepted Answer · answered Feb 12 '14 at 01:23

3

They probably meant can a class derive from two or more base classes, which it cannot. Confusing wording.

public abstract class A1;
public abstract class A2;
public abstract class B : A2;
public class C : A1, A2; // invalid
public class D : B; // valid

answered Feb 12 '14 at 01:23

Moho

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Not to nit pick too much, but "multiple inheritance" is a technical term, so the wording is not confusing, the asker simply isn't familiar with the term. – N_A Feb 12 '14 at 01:29
You are correct, but for most the question is more about knowing what the term "multiple inheritance" means and not the practice itself. If a simple pseudo code example was given, this person would not have incorrectly answered the question. – Moho Feb 12 '14 at 01:32

score 2 · Answer 4 · answered Feb 12 '14 at 01:29

Multiple inheritance allows a class to inherit from more than one parent class. C# doesn't allow multiple inheritace; that does not mean a class' characteristics can be inherited only once.

It is possible to use multiple "implementation" through interfaces:

interface IInterface
{
    ...
}

interface IAnotherInterface
{
    ...
}

class MyClass : IInterface, IAnotherInterface
{
    ...
}

score 0 · Answer 5 · answered Dec 14 '17 at 14:37

That is not considered as multiple inheretence but it is a multi-level or chain inheretence.

Multiple inheretence is when for example you have 3 classes A,B,and C. And class C is inheriting from classes A and B at the same time.

The problem with multiple inheretence and why it is not supported is that because if you have a method with the same name in both classes A and B with different implementation, and you want to use that method in class C, then class C will be confused of which of those method should it use. To prevent the confusion and ambiguity multiple inheretence is not supported in C#.

Does C# support multiple inheritance 4.0?

5 Answers5