C# using numbers in an enum

Question

This is a valid enum

public enum myEnum
{
  a= 1,
  b= 2,
  c= 3,
  d= 4,
  e= 5,
  f= 6,
  g= 7,
  h= 0xff
};

But this is not

public enum myEnum
{
  1a = 1,
  2a = 2,
  3a = 3,
};

Is there a way I can use an number in a enum? I already have code that would populate dropdowns from enums so it would be quite handy

Solution 1

No identifier at all in C# may begin with a number (for lexical/parsing reasons). Consider adding a [Description] attribute to your enum values:

public enum myEnum
{
    [Description("1A")]
    OneA = 1,
    [Description("2A")]
    TwoA = 2,
    [Description("3A")]
    ThreeA = 3,
};

Then you can get the description from an enum value like this:

((DescriptionAttribute)Attribute.GetCustomAttribute(
    typeof(myEnum).GetFields(BindingFlags.Public | BindingFlags.Static)
        .Single(x => (myEnum)x.GetValue(null) == enumValue),    
    typeof(DescriptionAttribute))).Description

Based on XSA's comment below, I wanted to expand on how one could make this more readable. Most simply, you could just create a static (extension) method:

public static string GetDescription(this Enum value)
{
    return ((DescriptionAttribute)Attribute.GetCustomAttribute(
        value.GetType().GetFields(BindingFlags.Public | BindingFlags.Static)
            .Single(x => x.GetValue(null).Equals(value)),
        typeof(DescriptionAttribute)))?.Description ?? value.ToString();
}

It's up to you whether you want to make it an extension method, and in the implementation above, I've made it fallback to the enum's normal name if no [DescriptionAttribute] has been provided.

Now you can get the description for an enum value via:

myEnum.OneA.GetDescription()

Solution 2

No, there isn't. C# does not allow identifiers to start with a digit.

Application usability note: In your application you should not display code identifiers to the end-user anyway. Think of translating individual enumeration items into user-friendly displayable texts. Sooner or later you'll have to extend the enum with an item whose identifier won't be in a form displayable to the user.

UPDATE: Note that the way for attaching displayable texts to enumeration items is being discusses, for example, here.

Solution 3

An identifier in C# (and most languages) cannot start with a digit.

If you can modify the code that populates a dropdown with the enumeration names, you could maybe have a hack that strips off a leading underscore when populating the dropdown and define your enum like so:

public enum myEnum
{
  _1a = 1,
  _2a = 2,
  _3a = 3
};

Or if you don't like the underscores you could come up with your own 'prefix-to-be-stripped' scheme (maybe pass the prefix to the constructor or method that will populate the dropdown from the enum).

Solution 4

No way. A valid identifier (ie a valid enumeration member) cannot start with a digit.

Solution 5

Enumerations are no different than variables in terms of naming rules. Therefore, you can't start the name with a number. From this post, here are the main rules for variable naming.

• The name can contain letters, digits, and the underscore character (_).

  • The first character of the name must be a letter. The underscore is also a legal first character, but its use is not recommended at the beginning of a name. An underscore is often used with special commands, and it's sometimes hard to read.

  • Case matters (that is, upper- and lowercase letters). C# is case-sensitive; thus, the names count and Count refer to two different variables.

  • C# keywords can't be used as variable names. Recall that a keyword is a word that is part of the C# language. (A complete list of the C# keywords can be found in Appendix B, "C# Keywords.")

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Comments

[Jim Mischel]

Better yet, the C# Language Specification section on Identifiers: msdn.microsoft.com/en-us/library/aa664670(v=VS.71).aspx

[John Bowen]

You can use DescriptionAttribute to associate a user-friendly string with each enum value and populate your dropdowns by extracting the attribute values instead of showing the raw enums.

[siride]

It'd be a lot easier to just use the Description attribute.

[Xavier]

Nice Solution; but is there an easier way to retreive the description shorter than these 4 lines ?

[will]

Should also point out that it's not limited to Enums, you can use it for anything you apply the DescriptionAttirbute to.

[kuklei]

I needed to define an enumeration for printer types that are 58MM and 80MM. These are user friendly displayable texts :P. Nevertheless, solved with _58mm

[Enigmativity]

Can you explain how (int) myEnum._1_5 is more readable than 0? And to start with, they're not equivalent in your code. It seems like it makes things hard to understand to me.

[Chandraprakash]

_1_5 in a remote code can be understood as 1.5, but 0 cannot be understood as 1.5. Thats how

[Enigmativity]

You're saying that you have a number, 1.5, in an array at position 0, so the most readable way to access the 1.5 is to do array[(int)myEnum._1_5]? That's crazy. If at compile-time you knew you needed 1.5 then double value = 1.5; is far better than double value = array[(int)myEnum._1_5];. Please tell me in what circumstance this increase in verbosity and indirection make sense?

[Chandraprakash]

I have a dropdown which has border values for line in PowerPoint which has values like 1, 1.5, 3, 5 etc which I store in enum. So it's easy for me to get/set index based on these value

[Enigmativity]

I think I'd have to see your code to understand why it's useful.

[Chandraprakash]

In simple words, when you only have choice to select handful of values from dropdown, and here readable in the sense, 0 doesn't say anything, but _1_5 you can understand what value is choosen.

[Enigmativity]

Again, I'd have to see actual code to hopefully understand why this is useful.