using System;

using System.Collections.Generic;

using System.Linq;

using System.Text.RegularExpressions;

using System.Reflection;

using System.Threading.Tasks;

public static class Program

{

        //private static System.Type DoesThingsType = System.Type.GetType(nameof(Thing));

    private static System.Type DoesThingsType = System.Type.GetType("Thing");

        public static void Main(string[] args)

        { 

            string funcName = "DoThing";

            MethodInfo mi = DoesThingsType.GetMethod(funcName, BindingFlags.NonPublic);

            string a = mi.Invoke(null, new object[] { 5 } ) as string;

        }

    }

internal static class Thing{

            public static string DoThing(int a) {

                return a+" is a number";

            }

        }

​