Storing string values as constants in the same manner as Enum

Question

I know there is a way to make enum work for string types with conversions galore - the code doesn't look pretty.

Does anyone know of any way to have something like this:

    public SOMESTRUCTURE SessionKeys : string
{
    value1 = "value1key",
    value2 = "value2key",
    name = "name"
}

so later in my code I could refer to it as:

SessionKeys.value1

Answer 1

This is about the best I've come up with. (I haven't compiled it, so the syntax may be off.)

public static class SessionKeys
{
    public const string Value1 = "Value1";
    public const string Value2 = "Value2";
    ...
}

Answer 2

Using C# 2.0 - I believe the best option is to use a static class with constants for your values, as suggested by John Fisher.

If you can use C# 3.0, you could use a standard enum, and a simple extension method to handle the conversion in a less objectionable manner.

Answer 3

See my answer here:
http://stackoverflow.com/questions/940002/getting-static-field-values-of-a-type-using-reflection

The difference between this and John Fisher's answer is that you can pass SessionKeys as function parameters and get the enum-like semantics you want.

The previous question asked for VB.Net, but a C# port shouldn't be that hard. In fact, here (untested):

public interface ICustomEnum<T>
{
    ICustomEnum<T> FromT(T value);
    T Value { get; }

    // Implement using a sealed class with a private constructor 
    // that accepts and sets the Value property, 
    // one shared readonly property for each desired value in the enum,
    // and implicit conversions to and from T.
    // Then see this link to get intellisense support
    // that exactly matches a normal enum:
    // http://stackoverflow.com/questions/102084/hidden-features-of-vb-net/102217#102217
    // Note that the completion list only works for VB.
}

/// <completionlist cref="SessionKeys"/>
public sealed SessionKeys: ICustomEnum<string>
{
    private string _value;
    public string Value { get { return _value; } } 

    private SessionKeys(string value)
    {
        _value = value;
    }

    private static SessionKeys _value1 = new MyStringEnum("value1key");
    public static SessionKeys value1 { get { return _value1;} } 

    private static MyStringEnum _value2 = new MyStringEnum("value2key");
    public static MyStringEnum value2 { get { return _value2;} } 

    public static ICustomEnum<string> FromString(string value) 
    {
        // use reflection or a dictionary here if you have a lot of values
        switch( value )
        {
            case "value1key":
                return value1;
            case "value2key":
                return value2;
            default:
                return null; //or throw an exception
        }
    }

    public ICustomEnum<string> FromT(string value) 
    {
        return FromString(value);
    }

    public static implicit operator string(SessionKeys item)
    {
        return item.Value;
    }

    public static implicit operator SessionKeys(string value)
    {
        return FromString(value);
    }
}

You don't really need the interface, but I keep it to remind me how to implement them.

Answer 4

The thing is that an enum isn't just a static class with a bunch of public numerical constants. An enum is a Type. With constants you lose type safety. You can achieve type safety if you make the static members of your class the same type as the class.

public sealed class SessionKey
{
    private _value; 
    private SessionKey( string value )
    {
     _value = value;
    }

    public string Value { get return _value; }

    public static readonly SessionKey Value1 = new SessionKey( "Value1" );
    public static readonly SessionKey Value2 = new SessionKey( "Value2" );
}

public class Something
{
    /* stuff */
    public void Foo( SessionKey sessionKey )
    {
     switch( sessionKey.Value )
     {
      case SessionKey.Value1.Value:
       DoBaz();
       break;
      case SessionKey.Value2.Value:
       DoBop();
       break;
      default:
       DoBar();
     }
    } 

    /* other stuff */
}