Generic enum as method parameter

Question

Given a constructor

public MyObject(int id){
    ID = id;
}

And two enums:

public enum MyEnum1{
    Something = 1,
    Anotherthing = 2
}

public enum MyEnum2{
    Dodo = 1,
    Moustache= 2
}

Is it possible to pass in a generic enum as a parameter of the constructor? I'm looking for a solution along the lines of:

public MyObject(enum someEnum){
    ID = (int)someEnum;
}

So you can do:

var newObject = new MyObject(MyEnum1.Something);
var anotherObject = new MyObject(MyEnum2.Dodo);

Answer 1

Another option would be:

public MyObject(Enum someEnum){
    ID = Convert.ToInt32(someEnum);
}

This way you can use it like you requested without having to cast to int each time you call your contstructors:

var newObject = new MyObject(MyEnum1.Something);
var anotherObject = new MyObject(MyEnum2.Dodo);

Answer 2

Why do you want to pass the enums, while you could pass integers ?

var newObject = new MyObject((int)MyEnum1.Something);
var anotherObject = new MyObject((int)MyEnum2.Dodo);

and use your first constructor :

public MyObject(int id){
    ID = id;
}

Answer 3

Just use a generic constructor:

class MyObject<T> {

    public MyObject(T someEnum) where T : struct, IConvertible
    {
        if (!typeof(T).IsEnum) 
            throw new ArgumentException("Not an enum");
        ID = Convert.ToInt32(someEnum);
    }
}

Now you can easily call it like this:

var m = new MyObject<MyEnum>(MyEnum1.Something);

But easier would be to pass the enum as integer to the constructor as mentioned in other answers.

EDIT: As of C# 7.3 you can use an enum-constraint right away:

class MyObject<T> where T: Enum { ... }

Answer 4

I have tried to do this with Attributes and it seems Enum as parameter in Attributes are not allowed. Therefore I had to do this workaround:

public MyCustomAttribute(object myEnumParameter)
{
    if (myEnumParameteris not Enum)
    {
        throw new ArgumentException("myEnumParameter is not an enum", 
            nameof(myEnumParameter));
    }

    MyEnumProperty = (Enum)myEnumParameter;
}

Answer 5

Well, if you really need to make this call generic for a wide variety of types, then IMHO you should use:

1. Type.IsEnum to check if your argument is really an Enum;
2. Enum.GetUnderlyingType to know what type is your argument is based on (it's not necessarily an Int32);

3. Now cast your object.

   public static Int32 GetAnInt<T>(T arg) where T : struct
   {
       if ((typeof(T).IsEnum))
       {
           var underlyingType = typeof(T).GetEnumUnderlyingType();
           if (underlyingType == typeof(Int32)
           || underlyingType == typeof(Int16)) //etc.
           {
               try
               {
                   dynamic value = arg;
                   var result = (Int32)value; // can throw InvalidCast!
                   return result;
               }
               catch
               {
                   throw;
               }
           }
           else
           {
               throw new InvalidCastException("Underlying type
                            is certainly not castable to Int32!");
           }
       }
       else
       {
           throw new InvalidCastException("Not an Enum!");
       }
   }
   

   That way you achieve the beautiful syntax of: var j = GetAnInt(MyEnum.FirstValue);

Answer 6

Are you using properties enum or parameters.

public enum Enum1{}
public Enum1 enum1 { get;set; }
public MyObject()
{
   ID = (int)enum1;
}

Just try it. I hope it is useful.