using System;

using System.Runtime;

using System.Reflection;

using System.Globalization;

​

// Type T in interface list is not an interface

//public struct NullableParsable<T> : Nullable<T> where T : struct { }

​

public struct NullableParsable<T> where T : struct

{

    T? nullableValue;

​

    public static T? Parse1(string s)

    {

        dynamic result = null;

        string tName = typeof(T).Name;

        switch(tName)

        {

            case "Int32": result = string.IsNullOrEmpty(s) ? null : (int?)int.Parse(s); break;

            case "Decimal": result = string.IsNullOrEmpty(s) ? null : (decimal?)decimal.Parse(s); break;

            default: throw new NotImplementedException("Unmanaged type: "+ tName);

        }

        return result;

    }

    public static T? Parse2(string s)

    {

        dynamic result = null;

        string tName = typeof(T).Name;

        switch (tName)

        {

            case "Int32":

            int intValue;

            result = int.TryParse(s, out intValue) ? (int?)intValue : null;

            break;

            case "Decimal":

            decimal decValue;

            result = decimal.TryParse(s, out decValue) ? (decimal?)decValue : null;

            break;

            default: throw new NotImplementedException("Unmanaged type: "+ tName);

        }

        return result;

    }

    public static T? Parse3(string s)

    {

        dynamic result = null;

        Type type = typeof(T);

        string tName = type.Name;

        MethodInfo methodInfo = type.GetMethod("Parse", new[] { typeof(string) });

        result = methodInfo.Invoke(null, new[] { s });

        return result;

    }

    public static T? Parse3(string s, IFormatProvider provider)

    {

        dynamic result = null;

        Type type = typeof(T);

        string tName = type.Name;

        MethodInfo methodInfo = type.GetMethod("Parse", new[] { typeof(string), typeof(IFormatProvider) });

        result = methodInfo.Invoke(null, new object[] { s, provider });

        return result;

    }

    public static T? Parse3(string s, NumberStyles style)

    {

        dynamic result = null;

        Type type = typeof(T);

        string tName = type.Name;

        MethodInfo methodInfo = type.GetMethod("Parse", new[] { typeof(string), typeof(NumberStyles) });

        result = methodInfo.Invoke(null, new object[] { s, style });

        return result;

    }

    public static T? Parse3(string s, NumberStyles style, IFormatProvider provider)

    {

        dynamic result = null;

        Type type = typeof(T);

        string tName = type.Name;

        MethodInfo methodInfo = type.GetMethod("Parse", new[] { typeof(string), typeof(NumberStyles), typeof(IFormatProvider) });

        result = methodInfo.Invoke(null, new object[] { s, style, provider });

        return result;

    }

    public static T? Parse4(string s)

    {

        Type type = typeof(T);

        string tName = type.Name;

        MethodInfo methodInfo = type.GetMethod("TryParse", new[] { typeof(string), type.MakeByRefType() });

        object[] args = new object[] { s, null };

        bool parsed = (bool)methodInfo.Invoke(null, args);

        dynamic result = parsed ? args[1] : null;

        return result;

    }

    public static T? Parse4(string s, IFormatProvider provider)

    {

        Type type = typeof(T);

        string tName = type.Name;

        MethodInfo methodInfo = type.GetMethod("TryParse", new[] { typeof(string), typeof(NumberStyles), typeof(IFormatProvider), type.MakeByRefType() });

        object[] args = new object[] { s, NumberStyles.Any, provider, null };

        bool parsed = (bool)methodInfo.Invoke(null, args);

        dynamic result = parsed ? args[3] : null;

        return result;

    }

    public static T? Parse4(string s, NumberStyles style)

    {

        Type type = typeof(T);

        string tName = type.Name;

        MethodInfo methodInfo = type.GetMethod("TryParse", new[] { typeof(string), typeof(NumberStyles), typeof(IFormatProvider), type.MakeByRefType() });

        object[] args = new object[] { s, style, CultureInfo.CurrentCulture, null };

        bool parsed = (bool)methodInfo.Invoke(null, args);

        dynamic result = parsed ? args[3] : null;

        return result;

    }

    public static T? Parse4(string s, NumberStyles style, IFormatProvider provider)

    {

        Type type = typeof(T);

        string tName = type.Name;

        MethodInfo methodInfo = type.GetMethod("TryParse", new[] { typeof(string), typeof(NumberStyles), typeof(IFormatProvider), type.MakeByRefType() });

        object[] args = new object[] { s, style, provider, null };

        bool parsed = (bool)methodInfo.Invoke(null, args);

        dynamic result = parsed ? args[3] : null;

        return result;

    }

}

public class Program

{

    public static void Main()

    {

        string s = "123.45";

        decimal d;

        decimal? d1 = decimal.TryParse(s, out d) ? (decimal?)d : null;

        decimal? d2 = string.IsNullOrEmpty(s) ? null : (decimal?)decimal.Parse(s);

        decimal? d3 = NullableParsable<decimal>.Parse1(s);

        decimal? d4 = NullableParsable<decimal>.Parse2(s);

        decimal? d5 = NullableParsable<decimal>.Parse3(s);

        decimal? d6 = NullableParsable<decimal>.Parse3(s, CultureInfo.CurrentCulture);

        decimal? d7 = NullableParsable<decimal>.Parse4(s);

        decimal? d8 = NullableParsable<decimal>.Parse4(s, CultureInfo.CurrentCulture);

        Console.WriteLine("Hello d1 = "+ d1);

        Console.WriteLine("Hello d2 = "+ d2);

        Console.WriteLine("Hello d3 = "+ d3);

        Console.WriteLine("Hello d4 = "+ d4);

        Console.WriteLine("Hello d5 = "+ d5);

        Console.WriteLine("Hello d6 = "+ d6);

        Console.WriteLine("Hello d7 = "+ d7);

        Console.WriteLine("Hello d8 = "+ d8);

        double? f = NullableParsable<double>.Parse1(s);

    }

}