Can enum parameter be optional in c#?

Question

I've used this helpful post to learn how to pass a list of Enum values as a parameter.

Now I would like to know whether I can make this parameter optional?

Example:

   public enum EnumColors
    {
        [Flags]
        Red = 1,
        Green = 2,
        Blue = 4,
        Black = 8
    }

I want to call my function that receives the Enum param like this:

DoSomethingWithColors(EnumColors.Red | EnumColors.Blue)

OR

DoSomethingWithColors()

My function should then look like what?

public void DoSomethingWithColors(EnumColors someColors = ??)
 {
  ...
  }

Answer 1

Yes it can be optional.

[Flags]
public enum Flags
{
    F1 = 1,
    F2 = 2
}

public  void Func(Flags f = (Flags.F1 | Flags.F2)) {
    // body
}

You can then call your function with or without parameter. If you call it without any parameter you'll get (Flags.F1 | Flags.F2) as the default value passed to the f parameter

If you don't want to have a default value but the parameter to be still optional you can do

public  void Func(Flags? f = null) {
    if (f.HasValue) {

    }
}

Answer 2

An enum is a value type, so you could use a nullable value type EnumColors?...

void DoSomethingWithColors(EnumColors? colors = null)
{
    if (colors != null) { Console.WriteLine(colors.Value); }
}

and then set the default value of EnumColors? to null

Another solution is to set EnumColors to an unused value...

void DoSomethingWithColors(EnumColors colors = (EnumColors)int.MinValue)
{
    if (colors != (EnumColors)int.MinValue) { Console.WriteLine(colors); }
}