Why can’t I have protected interface members?

by

I think everyone hammered the point of an interface having only public members, no implementation details. What you are looking for is an abstract class. 

public interface IOrange
{
    OrangePeel Peel { get; }
}

public abstract class OrangeBase : IOrange
{
    protected OrangeBase() {}
    protected abstract OrangePips Seeds { get; }
    public abstract OrangePeel Peel { get; }
}

public class NavelOrange : OrangeBase
{
    public override OrangePeel Peel { get { return new OrangePeel(); } }
    protected override OrangePips Seeds { get { return null; } }
}

public class ValenciaOrange : OrangeBase
{
    public override OrangePeel Peel { get { return new OrangePeel(); } }
    protected override OrangePips Seeds { get { return new OrangePips(6); } }
}

Edit: It is fair to argue that if we have a PlasticOrange that derives from a class Ornament, it can only implement IOrange and not the Seeds protected method. That is fine. An interface by definition is a contract between a caller and an object, not between a class and its subclasses. The abstract class is as close as we come to this concept. And that is fine. What you are essentially proposing is another construct in the language through which we can switch subclasses from one base class to another without breaking the build. To me, this doesn’t make sense.

If you are creating a subclass of a class, the subclass is a specialization of the base class. It should be fully aware of any protected members of the base class. But if you suddenly want to switch the base class out, it makes no sense that the subclass should work with any other IOrange.

I suppose you have a fair question, but it seems like a corner case and I don’t see any benefit from it to be honest.

More Related Contents:

  1. Why can’t I access C# protected members except like this?
  2. C# parameters in interface [closed]
  3. Multiple Inheritance in C#
  4. What are the default access modifiers in C#?
  5. Cast List to List
  6. Interfaces — What’s the point?
  7. Interface defining a constructor signature?
  8. How to Implement IComparable interface?
  9. Why implement interface explicitly?
  10. Why can’t we change access modifier while overriding methods in C#?
  11. How to determine if a type implements an interface with C# reflection
  12. Are there any reasons to use private properties in C#?
  13. Why can’t C# interfaces contain fields?
  14. Structs, Interfaces and Boxing [duplicate]
  15. How to choose between private and protected access modifier to encapsulate members between base and childs classes?
  16. Why Explicit Implementation of a Interface can not be public?
  17. Internal vs. Private Access Modifiers
  18. Interfaces vs. abstract classes [duplicate]
  19. When should I choose inheritance over an interface when designing C# class libraries? [closed]
  20. Is it safe for structs to implement interfaces?
  21. Creating a Math library using Generics in C#
  22. Is there a way to force a C# class to implement certain static functions?
  23. Non Public Members for C# Interfaces [closed]
  24. C#: Abstract classes need to implement interfaces?
  25. Why must an C# interface method implemented in a class be public?
  26. What is the meaning of the planned “private protected” C# access modifier?
  27. What is the use case for the (C# 7.2) “private protected” modifier?
  28. Implementations of interface through Reflection
  29. When should we use default interface method in C#?
  30. Does VLC media player have a C# interface? [closed]

Leave a Comment