Nesting class and enums types

Question

If an enum type is dedicate only to a specific class, does it make sense to declare it inside the class itself? I mean, would it help to understand that this enum type was designed to be used only with this class? Another option would be to put them inside the same namespace.

We also need to consider that another Dimension class could need a different enum type always called toleranceType.

Thanks.

public class Dimension
{
    public enum toleranceType
    {
        None,
        Symmetric,
        Deviation
    }

    public toleranceType ToleranceMode { get; set;}
}

Instead of:

public enum toleranceType
{
   None,
   Symmetric,
   Deviation
}

public class Dimension
{
    public toleranceType ToleranceMode { get; set;}
}

Answer 1

I don't think there is any compiled code difference between a nested enum and one in a namespace. You are just appending the container class or namespace to the full name.

However, Its usual to put classes in thier own files for readability.

Given that you don't get any functional difference, I would go with the convention of a new file for the enum, and just give it an appropriate namespace

If you have a pattern of many small classes each with its own specific enum, then I can see that nesting might be a neat solution though.

Answer 2

I would not nest the enum values as they are public. This is the recommendation from Microsoft on .Net design guidelines: https://docs.microsoft.com/en-us/dotnet/standard/design-guidelines/nested-types Namespaces are how you avoid naming collisions, not via nesting.

I'd also make the enum's name PascalCased.

Answer 3

Enums are often a sign that you aren't properly designing your objects and each enum value is better off being an object with a common interface, especially when a lot of your code is in if and switch statements based on values of an enum. Enums are more of a procedural coding concept and their use should be limited in truly object oriented code. Personally I find them most useful to make related constants more obvious and be more readable, especially when they aren't driving functionality themselves. This question has more about appropriate uses for enums in an object oriented design.

To answer your question more directly, keeping enums outside class definitions is usually the better choice, but only in situations where an enum is a good choice to begin with.