pre-defined constants for non-trivial data types

Question

My Goal: Create a C# class for predefined errors that have both an ID and a Message. Here was what I tried:

public class MyError
{
    public static readonly         


        

Answer 1

I would create a class that

• is sealed, to prevent it from being inherited
• has a private constructor, to prevent it from being instantiated from outside of the class
• provides properties with private setters, so they cannot be set from outside.

That would give you the following code:

public sealed class MyError
{
    public static readonly MyError OK = new MyError(0, "OK");

    public static readonly MyError Bad = new MyError(1, "Bad Stuff");

    private MyError(int id, string message)
    {
        this.ID = id;
        this.Message = message;
    }

    public int ID { get; private set; }

    public string Message { get; private set; }
}

Answer 2

Your properties should not be static because every instance of this class will have their own ID and Message, do you agree?

Answer 3

Your type is not mutable, but Code Analysis doesn't know that.
This warning is a false positive; you should suppress it.

---

To answer your edited question:

const can only be applied to primitives.
For custom types, static readonly is the only option.

As long as the type is properly immutable, it will work perfectly.

Answer 4

The type is not mutable. The Code Analysis gets confused by having public readonly fields.

You can fix the code analysis issue by making your public fields public properties:

public MyError(int id, string message)
{
    this.id = id;
    this.message = message;
}
private readonly int id;
private readonly string message;
public int Id { get { return id; } }
public string Message { get { return message; } }