R – Can an Interface contain an ENum

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Can an Interface contain an Enum?

I am using asp.net 2.0. Suddenly my code started having problems when I added an enum to the interface below. In it, LookUpType is an enum.

Public Interface ILookup
    Property ID() As Int32
    Property Text() As String
    Property Description() As String
    Property Status() As Status
    Property OrderID() As Int32
    ReadOnly Property LookUpType() As LookUpType
End Interface

Best Answer

You're question is a bit ambigious, it sounds like you could be asking either of the following

Can an Interface return a type which is an enum?

Yes. Enum's are not special in any way that prevents them being a return type on an interface

Can an Interface contain an enum definition?

Yes, this is completely legal in VB.Net. It is however not legal in C#

Interface IFoo
    Enum E1
        V1
    End Enum
    Function SomeMethod() As E1
End Interface

Related Solutions

Interface vs Base class

Let's take your example of a Dog and a Cat class, and let's illustrate using C#:

Both a dog and a cat are animals, specifically, quadruped mammals (animals are waaay too general). Let us assume that you have an abstract class Mammal, for both of them:

public abstract class Mammal

This base class will probably have default methods such as:

Feed
Mate

All of which are behavior that have more or less the same implementation between either species. To define this you will have:

public class Dog : Mammal
public class Cat : Mammal

Now let's suppose there are other mammals, which we will usually see in a zoo:

public class Giraffe : Mammal
public class Rhinoceros : Mammal
public class Hippopotamus : Mammal

This will still be valid because at the core of the functionality Feed() and Mate() will still be the same.

However, giraffes, rhinoceros, and hippos are not exactly animals that you can make pets out of. That's where an interface will be useful:

public interface IPettable
{
    IList<Trick> Tricks{get; set;}
    void Bathe();
    void Train(Trick t);
}

The implementation for the above contract will not be the same between a cat and dog; putting their implementations in an abstract class to inherit will be a bad idea.

Your Dog and Cat definitions should now look like:

public class Dog : Mammal, IPettable
public class Cat : Mammal, IPettable

Theoretically you can override them from a higher base class, but essentially an interface allows you to add on only the things you need into a class without the need for inheritance.

Consequently, because you can usually only inherit from one abstract class (in most statically typed OO languages that is... exceptions include C++) but be able to implement multiple interfaces, it allows you to construct objects in a strictly as required basis.

C# – How to enumerate an enum

foreach (Suit suit in (Suit[]) Enum.GetValues(typeof(Suit)))
{
}

Note: The cast to (Suit[]) is not strictly necessary, but it does make the code 0.5 ns faster.