gistfile1.cs

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Reflection;

#pragma warning disable 0414

namespace Enumに柔軟な拡張を追加する試み
{
    class Program
    {
        [RelatedLiterals(typeof(Hoge))]
        enum tesyEnum
        {
            [Obsolete]
            a,
            b,
        }

        public static class Hoge
        {
            static string b = "hoge";
        }

        [RelatedLiterals(typeof(Piyo))]
        enum tesyEnum2
        {
            c,
            d,
            e
        }

        public static class Piyo
        {
            static int c = 2;
            static double d = 0.5;
            static MyClass e = new MyClass();
        }

        public class MyClass { public override string ToString() { return "MyClass"; } }

        static void Main(string[] args)
        {

            //Console.WriteLine(tesyEnum.a.GetRelatedLiteral()); //RelatedLiteral属性つけてないと例外発生
            Console.WriteLine(tesyEnum.b.GetRelatedLiteral());
            Console.WriteLine(tesyEnum2.c.GetRelatedLiteral());
            Console.WriteLine(tesyEnum2.d.GetRelatedLiteral());
            Console.WriteLine(tesyEnum2.e.GetRelatedLiteral());
            Console.Read();
        }
    }


    [AttributeUsage(AttributeTargets.Enum, AllowMultiple = false, Inherited = false)]
    public class RelatedLiteralsAttribute : Attribute
    {
        public RelatedLiteralsAttribute(Type t)
        {
            Type = t;
        }
        public Type Type { get; private set; }
    }


    /// <summary>
    /// enum拡張メソッド用クラス
    /// </summary>
    public static class EnumExtension
    {
        /// <summary>
        /// RelatedLiteral属性に指定したリテラルを取得します。
        /// </summary>
        /// <param name="myself"></param>
        /// <returns></returns>
        public static dynamic GetRelatedLiteral(this Enum myself)
        {
            var type = myself.GetType();
            try
            {
                var attr = type.GetCustomAttributes(typeof(RelatedLiteralsAttribute), false).First() as RelatedLiteralsAttribute;
                var name = Enum.GetName(type, myself);
                var valType = attr.Type;
                var f = valType.GetField(name, BindingFlags.NonPublic | BindingFlags.Static);
                return f.GetValue(null);
            }
            catch
            {
                throw new CustomAttributeFormatException(type.Name + " にEnumAttr属性が指定されていません。");
            }
        }
    }
}