I don't understand inheritance with base classes

Question

My understanding of inheritance is pretty basic.

I want to create a base class, which implements IDisposable and then let other classes with functionality inherit from that base class, so that they share a base type.

It would allow me to put every object into one list, so that I can dispose of everything in one go, when I want to clean up. The thing is, a class in C# can only inherit once and otherwise only use interfaces.

Now, how can classes like Thread, inherit from my base class without me having to basically code the Thread class all over again?

It may sound dumb, but in short: I want to let already existing classes inherit a base class of my choosing without loosing its functionality. (So that all classes used in a project have a common base, to be summed up into one object type, for like List)

Is that even possible?

Answer 1

If your aim is to simply store a list of objects which can be disposed, then you want a List<IDisposable>. Any class which, directly or indirectly implements that interface can be stored therein.

var disposables = new List<IDisposable>();
disposables.Add(new MyClass1());
disposables.Add(new SomeClass());
disposables.Add(new AnotherClass());

disposables.ForEach(d => d.Dispose());

Whether this is a worthwhle pattern, I'm not convinced!

Answer 2

Example you given invlolves interface IDisposable. In C#, class can implement multiple interfaces.

On the other hand, in C# class may inherit from exactly one class.

Having said that, it is not always good idea to inherit from classes, as it very limiting. Instead I would suggest composition: wiki

For example, I would suggest something like composition design pattern (it is a small variation, as the composite does not have collection of objects, rather just one object):

public interface IFoo
{
    void DoFooStuff();
}

public class Foo : IFoo
{
    public void DoFooStuff() {...};
}

public class ShouldImplementFoo : IFoo
{
    // Composition, you need to initialize it some time
    private Foo _foo;
    
    public void DoFooStuff() { _foo.DoFooStuff(); }
}

EDIT

After rethinking your problem, you seem to want to put some set of objects (of different classes) in a list, so you can execute some defined action on each object in a list.

The simpliest is: define interface with your defined action:

public interface IMyIntf
{
    void MyDesiredAction();
}

And now, make all classes implement it. Now you might think "Well, now I need to implement this method everywhere..." - nothing like that! Just use adapter design pattern, for example, having class:

public class MyConcreteClass
{
    public void ActionIWishToExecuteOnThisObject() 
    { ... }
}

you just modify it to:

public class MyConcreteClass : IMyIntf
{
    public void ActionIWishToExecuteOnThisObject() 
    { ... }

    // implement interface
    public void MyDesiredAction()
    {
        ActionIWishToExecuteOnThisObject();
    }
}

Now, you can use some aggregate, like List<IMyIntf>, place all objects you are interested in there and do:

foreach(var item in myList)
    item.MyDesiredAction();

Answer 3

A class can inherits from an ancestor class (else Object, the root of all).

Also it can implements some interfaces (or none).

A class can have non implemented members as being abstract, so the class is abstract.

Also members can be virtual to enable polymorphism (abstract members are).

Once implemented, a thing is available in the class that can be instantiated for real if not abstract, and is available for all children too, except whose that are private which are hidden in subclass.

There is no need to repeat and that is one of the power of OOP.

Doing so, using abstraction, encapsulation, inheritance and polymorphism, after stuying the real world and the domain where we work, we can design a projection of this real world, a view in our mind, with concepts having data (fields and properties) and operations (methods), classed in artifacts (objects) and things like relations, composition, aggregation, interfaces, components, controls, and so on.

Thus we can factorize processings to not repeat like for example:

• Having a Animal class and Cat and Dog child classes,
• We put in animal the Size and the Color aspect,
• As well as the Eat and Walk methods implemented for all animals,
• And an abstract non-implemented DoSound.

Therefore:

• In concrete classes Cat and Dog we don't implement again the things,
• Except DoSound that is particular for each real animal gender.

Concerning interfaces, they are virtual contracts.

For example we can have animals and buildings that have nothing in common, at first look (we will not go back to atoms and photons), but we want to be able to manage instances of objects like cat and dog, as well as house and museum to take a photo.

To acheive that we define an interface IPhotoTaking and when defining previous classes, we add that they implements this interface.

Code sample:

public interface IPhotoTaking
{
  Image TakePhoto();
}

public abstract class Animal : IPhotoTaking
{
  public int Size { get; set; }
  public Color Color { get; set; }
  public void Eat() { ... }
  public void Walk() { ... }
  public abstract void DoSOund();
  public Image TakePhoto();
}

public class Cat : Animal // no need to repeat IPhotoTaking
{
  public override void DoSound() { ... }
}

public class Dog : Animal
{
  public override void DoSound() { ... }
}

public abstract class Building :IPhotoTaking
{
  public Image TakePhoto();
}

public class House : Building
{
}

public class Museum : Building
{
}

Now having this list we can use polymorphism like that:

var animals = new List<Animal>();

foreach ( var animal in animals )
  animal.DoSound();

Also without polymorphism and because C# does not support true polymorphism with the diamond operator yet applied on List<> here, we can use the interface like that:

var items = new List<IPhotoTaking>();

foreach ( var item in items )
  item.TakePhoto();

Remark: if taking a photo may be different for each types, we can set it virtual to specialize its implementation in each.

OOP Basic Principles

What is abstraction in C#?

How to choose between public, private and protected access modifier?

Association, Composition and Aggregation

What is polymorphism?

What is the difference between an interface and a class?

About the lack of true generic polymorphism and the missing diamond operator in C#