Multiple Inheritance and Objects C#

Question

Sorry didn't get any funky title for the question.

I had been taught that .Net(C#) doesn't support Multiple Inheritance. But looking at the foo example below I wonder is this really truth ??

class fooList
{
    public int Index()
    {
        return 0;
    }
}    
class foo : fooList
{
    public foo()
    { }
}
class testFoo
{
    void test()
    {
        foo obj = new foo();

        // From object
        obj.Equals(obj);
        obj.GetHashCode();
        obj.GetType();
        obj.ToString();

        // From fooList
        obj.Index();
    }
}

As we can see that I have a class fooList and a class foo which inherits fooList according to the sayings(C# doesn't support Multiple Inheritance) the object of class foo should have only one method which is Index() from the fooList class, But it has more methods from the object class. It clearly indicates that by default all the classes inherit object class. So questions raises

1. Is it really completely true that C# doesn't support Multiple Inheritance ?
2. I guess it supports it at CLR level, Than why it doesn't support it in coding ?

Answer 1

C# does not support multiple inheritance of classes at a single level. C# does support multiple levels of inheritance in a hierarchy. What you are seeing is that at the top of your inheritance hierachy is System.Object, which is the top level base class for classes and structs in .NET.

What you cannot have is:

class A { }
class B { }
class C : A, B { }

What you can have:

class A { }
class B : A { }
class C : B { } 

Make sense?

For a bit more completeness, C# does allow you to simulate multiple inheritance via the usage of interfaces. So let's walk it back.

class A { }
interface B { }
class C : A, B { } // legal

In this example, the declaration of C is legal, and you would need to implement the various members that interface B defines as part of C.

Answer 2

Multiple Inheritance is not what you're seeing here. Multiple Inheritance means that a class derives from two base classes "in parallel", like maybe this:

public class Test : Base1, Base2 {}

That is not possible.

What you're seeing here (and this works in any object oriented language) is that of course a class A inherits methods and properties from all the entire hierarchy.

For example:

public class Test : Base {}

inherits all methods from Base and Object, if Base is directly derived from Object.

So if you have this hierarchy:

public class Base : Object {}
public class A : Base {}

Base inherits all methods and properties from Object, and A inherits all methods and properties from Base and thus also from Object.

Otherwise it would not be possible to build class hierarchies.

Answer 3

You are showing example of multi label inheritance and not multiple inheritance.

Multiple inheritance means a single class can inherit more than one class.

class A: B,C

Which is not true in case of c#

Answer 4

You are missunderstanding multiple inheritance. A class can inherit a class which already inherits another class. But a class cannot inherit two or more different classes at the same time.

// Default inheritance from Object.
// Class A inherits System.Object
class A     

// Simple inheritance. This is not multiple inheritance.   
// Class B inherits class A, which inherits Object
class B : A     

// Simple inheritance. This is not multiple inheritance.
// Class C inherits class B, which inherits class A, which inherits Object
class C : B  

// Default inheritance from Object.
// Class D inherits System.Object
class D     

// Multiple inheritance
// Class E inherits both class A and class D
class E : A, D

// Multiple inheritance
// Class F inherits both class A and class B
class F : A, B

// Multiple inheritance
// Class G inherits both class C and class D
class G : C, D