Suppose you have the following scenario: You have a function that can return multiple return types codes via an enum value. For each of those enum values, you want to inform the user the result of the operation by some user friendly string.
A common implementation I see is some sort of switch statement that resolves enumerations to a string by way of a switch statement or hash table or something. And whenever that string is needed, call into said method.
And although this is viable, this creates a disconnect between the enum and it’s actual string literal definition. In addition, for each new enumeration value, that giant switch statement needs to be updated with a new string value. If there were only a clean way to map an enum to a string value automatically… and there is! With clever usage of attributes, reflection, and extension methods, one can do something like this:
using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Linq.Expressions;
namespace EnumString
{
[AttributeUsage(AttributeTargets.Field)]
class EnumStringAttribute : Attribute
{
string myValue;
public EnumStringAttribute(string value)
{
myValue = value;
}
public override string ToString()
{
return myValue.ToString();
}
}
static class ExtensionMethods
{
public static string ToUserString(this Enum enumeration)
{
var type = enumeration.GetType();
var field = type.GetField(enumeration.ToString());
var enumString = (from attribute in field.GetCustomAttributes(true) where attribute is EnumStringAttribute select attribute).FirstOrDefault();
if (enumString != null)
return enumString.ToString();
return enumeration.ToString();
}
}
enum AuthenticationResult
{
[EnumString("This username is not registered.")]
NotRegistered,
[EnumString("Incorrect password.")]
BadPassword,
[EnumString("Logging in...")]
Success,
}
class Program
{
static void Main(string[] args)
{
Console.WriteLine(AuthenticationResult.BadPassword.ToUserString());
Console.WriteLine(AuthenticationResult.NotRegistered.ToUserString());
Console.WriteLine(AuthenticationResult.Success.ToUserString());
}
}
}
Delaring string values can simply be done inline, and the usage is simple as well! Just call the new extension method to get your user friendly string!
(Of course, for localization, you may want to map the enum to a string resource rather than a hard coded string value; but a similar approach can be used.)
