Non-unique enum values

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Actually you’re already defining a struct… Behind the scenes an enum is just a struct (but which derives from System.Enum) and the values of the enum are defined as constants (you can verify this with ILDASM).

Your enum definition translates into the following pseudo C# code:

public struct Color : System.Enum
{
    public const int Red = 1;
    public const int Blue = 1;
    public const int Green = 1;
}

The above code won’t compile in C# because the compiler doesn’t allow defining a struct with an explicit base class, but that’s what it emits for an enum definition.

Since there is no problem with a type that contains an multiple constants that have the same value, there is no problem with the enum definition.

But since the enum does not have unique values you might have an issue when converting into this enum.
For example the following two line of codes will return the enum value Red, because the first value is arbitrarily selected. 

Color color1 = (Color)1;
Color color2 = (Color)Enum.Parse(typeof(Color), "1");

Strictly speaking the enum value is not Red, it is 1, but when you print out the value you’ll see Red.

Also, the following boolean is true which looks a bit weird…

// true (Red is Green??)
bool b = Color.Red == Color.Green;

At the bottom line this is perfectly legal, but it’s up to you to use it when it makes sense…

Here is a direct link to the section of my .NET tutorial that discusses enumerations under the hood: http://motti.me/c1E

More Related Contents:

  1. How to declare enums in C#
  2. Convert a string to an enum in C#
  3. Enum “Inheritance”
  4. How to get C# Enum description from value? [duplicate]
  5. Can my enums have friendly names? [duplicate]
  6. C# vs Java Enum (for those new to C#)
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  8. Changing the value of an element in a list of structs
  9. How does native implementation of ValueType.GetHashCode work?
  10. How can I cast int to enum in C#?
  11. What is the tilde (~) in the enum definition?
  12. WPF Binding a ListBox to an enum, displaying the Description Attribute
  13. How to set enum to null
  14. Modify Struct variable in a Dictionary
  15. Why enums require an explicit cast to int type?
  16. How do you pass multiple enum values in C#?
  17. How to convert a character in to equivalent System.Windows.Input.Key Enum value?
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  19. Enum to Dictionary in C#
  20. How to prevent duplicate values in enum?
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  23. How to convert from System.Enum to base integer?
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  25. Using GetHashCode for getting Enum int value
  26. Why is it possible to instantiate a struct without the new keyword?
  27. Cycle in the struct layout that doesn’t exist
  28. C# numeric enum value as string
  29. Are structs ‘pass-by-value’?
  30. MVC 5.1 Razor DisplayFor not working with Enum DisplayName

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