C# Enums and possibly having a default value?

Question

So I have the following enum and I need it to have a "None" item which is used by other code, like the method: GetCompassDirectionFromUnitVector as shown below:

    public enum CompassDirection
{
    North = 90,
    Northeast = 45,
    East = 0,
    Southeast = -45,
    South = -90,
    Southwest = -135,
    West = 180,
    Northwest = 135,
    None = null
}


/// <summary>
/// Returns compass direction (North, Southwest, etc.) from a given direction unit vector. 
/// Returns CompassDirection.None if given Vector is not a unit vector.
/// </summary>
/// <param name="vec">Direction unit vector</param>
/// <returns></returns>
public static CompassDirection GetCompassDirectionFromUnitVector(Vector vec)
{
    Dictionary<Vector, CompassDirection> list = new Dictionary<Vector, CompassDirection>()
    {
        {new Vector(0, 0), CompassDirection.None},
        {new Vector(0, 1), CompassDirection.North},
        {new Vector(0, -1), CompassDirection.South},
        {new Vector(1, 0), CompassDirection.East},
        {new Vector(-1, 0), CompassDirection.West},
        {new Vector(1, 1), CompassDirection.Northeast},
        {new Vector(1, -1), CompassDirection.Southeast},
        {new Vector(-1, 1), CompassDirection.Northwest},
        {new Vector(-1, -1), CompassDirection.Southwest},
    };
    if (list.ContainsKey(vec))
    {
        return list[vec];
    }
    return CompassDirection.None;
}

But I'm writing the following method:

   Angle GetAngleFromCompassDirection(CompassDirection dir)

So having the angles in the enum values is incredibly useful here. But integers aren't nullable so having that "None" value enum is invalid.

How do I go around this?

Don't post screenshots, paste the code directly into the question. — Quantic, Oct 27 '16 at 17:12
You could use the nullable version of your enum `CompassDirection?` — juharr, Oct 27 '16 at 17:13
Copy and Pasting code is easier than posting a snapshot - try it — Ňɏssa Pøngjǣrdenlarp, Oct 27 '16 at 17:13
"0" is the default for an enum as stated [here](http://stackoverflow.com/questions/4967656/what-is-the-default-value-for-enum-variable). If 0 is an actual value then there is no way to disambiguate between the default value and the actual 0 value. — Quantic, Oct 27 '16 at 17:14
Alright I thought posting C# here was as awful as Lua but apparently not :) — Elmub, Oct 27 '16 at 17:14
@user3524922 no - _"The approved types for an enum [value] are byte, sbyte, short, ushort, int, uint, long, or ulong."_ — stuartd, Oct 27 '16 at 17:17
What's the return value for GetAngleFromCompassDirection when dir is None? — FacticiusVir, Oct 27 '16 at 17:19
@user3524922 [`Nullable`](https://msdn.microsoft.com/en-us/library/b3h38hb0(v=vs.110).aspx) which has the shorthand of just adding a `?` after the type instead, so `int?` is short for `Nullable`. And you could change your return type to `CompassDirection?` and then just `return null;` at the end. — juharr, Oct 27 '16 at 17:21

score 1 · Accepted Answer · answered Oct 27 '16 at 17:27

The default for an Enum value will always be Zero (0). What I would recommend is for you to change your implementation to:

public static CompassDirection? GetCompassDirectionFromUnitVector(Vector vec)
{
    Dictionary<Vector, CompassDirection> list = new Dictionary<Vector, CompassDirection>()
    {
        {new Vector(0, 0), CompassDirection.None},
        {new Vector(0, 1), CompassDirection.North},
        {new Vector(0, -1), CompassDirection.South},
        {new Vector(1, 0), CompassDirection.East},
        {new Vector(-1, 0), CompassDirection.West},
        {new Vector(1, 1), CompassDirection.Northeast},
        {new Vector(1, -1), CompassDirection.Southeast},
        {new Vector(-1, 1), CompassDirection.Northwest},
        {new Vector(-1, -1), CompassDirection.Southwest},
    };
    if (list.ContainsKey(vec))
    {
        return list[vec];
    }
    return null;
}

(Note the Nullable return Type) You can then treat null valus as you would otherwise treat CompassDirection.None.

If I can return null, then the "None"-value gets kinda pointless. Thanks! — Elmub, Oct 27 '16 at 18:00

C# Enums and possibly having a default value?

1 Answers1