Question

I am looking to build a java-style enum pattern for C# that also supports inheritance. I’m having trouble with yield return. Specifically, returning the BaseEnum’s Values from the ChildEnum’s Values property.

public class BaseEnum {
    public static readonly BaseEnum A = new BaseEnum("A");
    public static readonly BaseEnum B = new BaseEnum("B");
    public static readonly BaseEnum C = new BaseEnum("C");

    public static IEnumerable<BaseEnum> Values {
        get {
            yield return A;
            yield return B;
            yield return C;
        }
    }

    public readonly String Name;

    protected BaseEnum(String name) {
        this.Name = name;
    }

    public static void TestMain() {
        Console.WriteLine("BaseEnum, should print (A,B,C):");
        foreach(BaseEnum e in BaseEnum.Values) {
            Console.WriteLine(e.Name);
        }
        Console.WriteLine("BaseEnum in ChildEnum, should print (A,B,C,D,E):");
        foreach(BaseEnum e in ChildEnum.Values) {
            Console.WriteLine(e.Name);
        }
        Console.WriteLine("ChildEnum in ChildEnum, should print (D,E):");
        foreach(ChildEnum e in ChildEnum.Values) {
            Console.WriteLine(e.Name);
        }
    }
}

class ChildEnum : BaseEnum {
    public static readonly ChildEnum D = new ChildEnum("D");
    public static readonly ChildEnum E = new ChildEnum("E");

    new public static IEnumerable<BaseEnum> Values {
        get {
            // yield return BaseEnum.Values; // This is what I want to do. It gives the error message below:
            // Cannot implicitly convert type 'System.Collections.Generic.IEnumerable<Abra.Workshop.EnumABC>' 
            // to 'Abra.Workshop.EnumABC'. An explicit conversion exists (are you missing a cast?)

            yield return D;
            yield return E;
        }
    }

    public ChildEnum(string name)
        : base(name) {
    }
}

/* Output!
BaseEnum, should print (A,B,C):
A
B
C
BaseEnum in ChildEnum, should print (A,B,C,D,E):
D
E
ChildEnum in ChildEnum, should print (D,E):
D
E
*/

Answer 1

Use

foreach (var b in BaseEnum.Values)
  yield return b;

You need to unwrap BaseEnum.Values into individual elements.

Or replace it with a LINQ expression:-

return BaseEnum.Values.Concat(new[]{ D, E });