interface ISmth
    {
        void DoSmth<T>(T value);
    }

    class Smth : ISmth
    {
        public void DoSmth<T>(T value)
        {
            //DoSmthSmth(value); // ошибка
            if (value is string)
                DoSmthSmth(value as string);
            else if(value is List<string>)
                DoSmthSmth(value as List<string>);
            else if(value is Exception)
                DoSmthSmth(value as Exception);
        }

        void DoSmthSmth(string value) {}
        void DoSmthSmth(List<string> value) {}
        void DoSmthSmth(Exception value) {}
    }

    class Program
    {
        static void Main(string[] args)
        {
            ISmth smth = new Smth();

            smth.DoSmth("string");
            smth.DoSmth(new List<string> { "l", "i", "s", "t" });
            smth.DoSmth(new Exception("exception"));
        }
    }

interface ISmth
    {
        void DoSmthWithString(string value);
        void DoSmthWithListOfStrings(List<string> value);
        void DoSmthWithException(Exception value);
    }

        public void DoSmth<T>(T value)
        {
            dynamic mv = value;			
	    DoSmthSmth(mv);
        }

namespace NLog.Interface
{
  public interface ILogger
  {

    void Log<T>(LogLevel level, T value);

    void Log<T>(LogLevel level, IFormatProvider formatProvider, T value);

  }
}

void LogException(LogLevel level, [Localizable(false)] string message, Exception exception);

interface ISmth
    {
        void DoSmth<T>(T value);
    }