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Alias for enum values

Is it possible to alias enum values?

Someone here showed me this as part of another question, where for example "Daily" and "DY" should map to the same value:

public enum TimePeriod
  {
    Unknown,
    Daily,
    Weekly,
    Biweekly,
    Monthly,
    Yearly,
    AbbrevStart,
    Unk = Unknown,
    DY = Daily,
    WK = Weekly,
    BW = Biweekly,
    MO = Monthly,
    YR = Yearly,
    AbbrevEnd
  }

But it doesn't seem to me like that would actually work.  Is there documenation on this?
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mrichmon
Asked:
mrichmon
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2 Solutions
 
kmaicorpCommented:
Yes it does work, we used it in our system as well, we even define an enum like so

public enum MyEnum
{
  val1 = 1,
  val2 = 2,
  val3 = 4,
  val4 = val1 | val2
}

As far I documentation, I don't remember where I've seen it before. Just try it in your code and see if it works.
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Bob LearnedCommented:
What doesn't work about it?

Bob
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mrichmonAuthor Commented:
kmaicorp,

You are only using a base int type that is not what I am asking about here.  Notice that none of your values overlap.  The | works because you are going in powers of 2.  That is n

anyoneis,

That is the basic documentation for enums and does not address this isse.

TheLearnedOne,

Okay I played with it some more and actually it does work.  I think the AbbrevStart and AbbrevEnd were causing issues, but those can just be excluded.  However is there any documentation that talks about aliasing to earlier enum values?  Also is there a way to just have one set show, but both accpeted for each value?  I guess we are just looking for documenation on how aliasing works so we can see what is and is not possible so we can evaluate if it meets our needs.
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gregoryyoungCommented:
kmai

You are not assigning two items to the same value

public enum MyEnum
{
  val1 = 1,
  val2 = 2,
  val3 = 4,
  val4 = val1 | val2
}

assigns val4 a value of 3 (2 | 1) 0010 | 0010 = 0011 = 3

You can do things like this ..

        enum foo {
            Option1 = 1,
            Option2 = 1,
            Option3
        }

or

        enum foo {
            Option1 = 1,
            Option2 = Option1,
            Option3
        }

But you will sometimes get odd behavior when dealing with things like reflection (just happen to have this code from a flags question but it illustrates the point nicely)

            foo f = foo.Option1 | foo.Option2 | foo.Option3;
            foreach(int value in Enum.GetValues(typeof(foo))) {
                if (((int) f & value) > 0) {
                    Console.WriteLine(Enum.GetName(typeof(foo), value) + " set");
                } else {
                    Console.WriteLine(Enum.GetName(typeof(foo), value) + " not set");
                }
            }

Notice that getname returns Option2 for both.

Cheers,

Greg
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mrichmonAuthor Commented:
Anyone?

>>is there a way to just have one set show, but both accpeted for each value?  I guess we are just looking for documenation on how aliasing works so we can see what is and is not possible so we can evaluate if it meets our needs.
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anyoneisCommented:
Good luck! I haven't been able to find any documentation. It worked this way in C++ so I was not surprised to see it working in C#. The language definition is mute on the point.

David
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anyoneisCommented:
From the 1.0 C# Specification:

"Multiple enum members may share the same associated value. The example
enum Color
{
      Red,
      Green,
      Blue,
      Max = Blue
}
shows an enum in which two enum members—Blue and Max—have the same associated value."

You will find this resource at: http://msdn.microsoft.com/vcsharp/programming/language/default.aspx

David
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gregoryyoungCommented:
Aliasing like this will work .. you just have to be very careful when dealing with things like reflection as it will associated only a single item to the value (In particular the GetName function).
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