c# - Sort enums in declaration order

Question

public enum CurrencyId
{
    USD = 840,
    UAH = 980,
    RUR = 643,
    EUR = 978,
    KZT = 398,
    UNSUPPORTED = 0
}

Is there any way to sort results of Enum.GetValues(typeof(CurrencyId)).Cast<CurrencyId>() by order they are declared in .cs file (USD, UAH, RUR, EUR, KZT, UNSUPPORTED), not by their underlying code? Personally, I believe the answer is 'no', because original order is lost in binaries, so... how can I implement the task?

Answer 1

Here is version with custom attribute:

[AttributeUsage(AttributeTargets.Field, AllowMultiple = false)]
public class EnumOrderAttribute : Attribute
{
    public int Order { get; set; }
}


public static class EnumExtenstions
{
    public static IEnumerable<string> GetWithOrder(this Enum enumVal)
    {
        return enumVal.GetType().GetWithOrder();
    }

    public static IEnumerable<string> GetWithOrder(this Type type)
    {
        if (!type.IsEnum)
        {
            throw new ArgumentException("Type must be an enum");
        }
        // caching for result could be useful
        return type.GetFields()
                               .Where(field => field.IsStatic)
                               .Select(field => new
                                            {
                                                field,
                                                attribute = field.GetCustomAttribute<EnumOrderAttribute>()
                                            })
                                .Select(fieldInfo => new
                                             {
                                                 name = fieldInfo.field.Name,
                                                 order = fieldInfo.attribute != null ? fieldInfo.attribute.Order : 0
                                             })
                               .OrderBy(field => field.order)
                               .Select(field => field.name);
    }
}

Usage:

public enum TestEnum
{
    [EnumOrder(Order=2)]
    Second = 1,

    [EnumOrder(Order=1)]
    First = 4,

    [EnumOrder(Order=3)]
    Third = 0
}

var names = typeof(TestEnum).GetWithOrder();
var names = TestEnum.First.GetWithOrder();