非ジェネリック版 Enum.TryParse

EnumEx.cs

using System;
using System.Collections.Generic;
using System.Reflection;


class Program
{
    static void Main(string[] args)
    {
        object vt1;
        bool b1 = EnumEx.TryParse(typeof(FizzBuzz), "Buzz", out vt1);
        Console.WriteLine("{0} {1}", b1, vt1);
        object vt2;
        bool b2 = EnumEx.TryParse(typeof(FizzBuzz), "-", out vt2);
        Console.WriteLine("{0} {1}", b2, vt2);
    }
}

enum FizzBuzz
{
    Fizz,
    Buzz
}

class EnumEx
{
    private delegate Tuple<bool, object> Parser(string value);
    private static readonly MethodInfo genericMethod = typeof(EnumEx).GetMethod("DoTryParse", BindingFlags.NonPublic | BindingFlags.Static);
    private static readonly Dictionary<Type, Parser> delegates = new Dictionary<Type, Parser>();

    public static bool TryParse(Type enumType, string value, out object result)
    {
        if (enumType == null)
        {
            throw new ArgumentNullException("enumType");
        }
        if (!enumType.IsEnum)
        {
            throw new ArgumentException("enumType is not Enum");
        }
        if (value == null)
        {
            result = (ValueType)Activator.CreateInstance(enumType);
            return false;
        }
        Parser p;
        if (!delegates.TryGetValue(enumType, out p))
        {
            p = (Parser)Delegate.CreateDelegate(typeof(Parser), genericMethod.MakeGenericMethod(enumType));
            delegates[enumType] = p;
        }
        var tuple = p.Invoke(value);
        result = tuple.Item2;
        return tuple.Item1;
    }

    private static Tuple<bool, object> DoTryParse<TEnum>(string value)
        where TEnum : struct
    {
        TEnum e;
        bool success = Enum.TryParse<TEnum>(value, out e);
        return Tuple.Create(success, (object)e);
    }
}