Question

I have an enum, suppose it is called sports:

enum Sports
{
  Baseball = 1,
  Basketball = 2,
  Football = 4,
  Hockey = 8,
  Soccer = 16,
  Tennis = 32,
  etc...
}

I would basically like to add an extension method that clears a mask bit like this:

Sports Mask = Sports.Baseball | Sports.Football | Sports.Tennis; //37
Mask.Clear(Sports.Baseball);
// Mask = Football | Tennis

This is the extension method I’ve come up with, it doesn’t work. Clear doesn’t affect Mask, the value remains 37. I’m not sure I can modify the this portion from within the extension method. Is there some other way to accomplish this?

public static void Clear<T>(this Enum value, T remove)
{
  Type type = value.GetType();
  object result;

  if (type.Equals(typeof(ulong)))
  {
    result = Convert.ToUInt64(value) & ~Convert.ToUInt64((object)remove);
  }
  else
  {
    result = Convert.ToInt64(value) & ~Convert.ToInt64((object)remove);
  }

  value = (Enum)Enum.Parse(type, result.ToString());
}

Answer 1

Because enums are value types, so that you modified the parameter only. You can return the modified value and assign it to the original variable.

public static T Clear<T>(this Enum value, T remove) { ... }
mask = mask.Clear(Sports.Baseball);
//just like
//DateTime dt = DateTime.Now;
//dt = dt.AddHour(1);

And by the way, I don’t think it worth an extension method here. Why not just simply use:

mask = mask & ~Sports.BaseBall;
mask = mask & ~anotherMask;

Your extension method is very inefficient because of (un)boxing.