How to get only the first value from a flags enum value and get it in the order they were added

Question

I have the following code:

[Flags()]
public enum Foo
{
    Unknown = 0x00,
    A = 0x01,
    B = 0x02,
    C = 0x04,
    D = 0x08,
}

public static class Extensions
{
    public static List<Foo> AsList(this Foo types)
    {
        List<Foo> list = new List<Foo>();
        foreach(Foo sT in Enum.GetValues(typeof(Foo)))
        {
            if ((sT & types) == sT) list.Add(sT);
        }
        return list;
    }

}

class Program
{
    static void Main(string[] args)
    {
        Foo foo1 = Foo.A | Foo.B | Foo.C;
        Foo foo2 = Foo.C | Foo.B;

        Foo firstInfoo1 = foo1.AsList()[0];
        Foo firstInFoo2 = foo2.AsList()[0];
    }
}

Now firstInfoo1 and firstInfoo2 both come out be Unknown which i don't want. Seeing the code that is there should i return the index [1] always, as so : foo1.AsList()[1]?

Is that a good idea?? Any ideas on the error, bound checking that would need to be done.

Also lets have a look at foo2, i added Foo.C first and Foo.B second. Is there any way i can get from AsList Foo.C and not Foo.B, i.e. the first in order they were added.

Is that possible?

Appreciate the help.

Thanks

Answer 1

Either remove the Unknown value, or do this:

if ((int)sT != 0 && (sT & types) == sT) list.Add(sT);

A little background: those OR-ed enums are not stored like that in memory, they are stored as a simple integer number, so .NET doesn't known how that enum was constructed.