How to prevent duplicate values in enum?

Question

I wonder is there a way to prevent an enum with duplicate keys to compile?

For instance this enum below will compile

public enum EDuplicates
{
    Unique,
    Duplicate = 0,
    Keys = 1,
    Compilation = 1
}

Although this code

Console.WriteLine(EDuplicates.Unique);
Console.WriteLine(EDuplicates.Duplicate);
Console.WriteLine(EDuplicates.Keys);
Console.WriteLine(EDuplicates.Compilation);

Will print

Duplicate
Duplicate
Keys
Keys

Answer 1

Here's a simple unit test that checks it, should be a bit faster:

[TestMethod] public void Test() {   var enums = (myEnum[])Enum.GetValues(typeof(myEnum));   Assert.IsTrue(enums.Count() == enums.Distinct().Count()); } 

Answer 2

This isn't prohibited by the language specification, so any conformant C# compiler should allow it. You could always adapt the Mono compiler to forbid it - but frankly it would be simpler to write a unit test to scan your assemblies for enums and enforce it that way.

Answer 3

Unit test that checks enum and shows which particular enum values has duplicates:

[Fact]
public void MyEnumTest()
{
    var values = (MyEnum[])Enum.GetValues(typeof(MyEnum));
    var duplicateValues = values.GroupBy(x => x).Where(g => g.Count() > 1).Select(g => g.Key).ToArray();
    Assert.True(duplicateValues.Length == 0, "MyEnum has duplicate values for: " + string.Join(", ", duplicateValues));
}