public interface IConstraint<T>
    {
        bool Satisfies(T value);
    }
    public class Constrained<T, Constraint>
        where Constraint : IConstraint<T>, new()
    {
        public static bool TryCreate(T val, out Constrained<T, Constraint> result)
        {
            var c = new Constraint();
            var success = c.Satisfies(val);
            result = success ? new Constrained<T, Constraint>(val) : default;
            return success;
        }
        private Constrained(T str)
        {
            Value = str;
        }
        public T Value { get; set; }

        public static implicit operator T(Constrained<T, Constraint> val) => val.Value;
        public override string ToString() => Value.ToString();
    }
    public class NonEmptyStringConstraint : IConstraint<string>
    {
        public bool Satisfies(string value)
            => !string.IsNullOrWhiteSpace(value);
    }
    class Program
    {
        static Constrained<string, NonEmptyStringConstraint> ReadNonEmptyString()
        {
            string str;
            Constrained<string, NonEmptyStringConstraint> res;
            do
            {
                str = Console.ReadLine();
            } while (!Constrained<string, NonEmptyStringConstraint>.TryCreate(str, out res));
            return res;
        }
        static void Main(string[] args)
        {
            Console.WriteLine("What is your name? ");
            var name = ReadNonEmptyString();
            Console.WriteLine("What is your quest? ");
            var quest = ReadNonEmptyString();
            Console.WriteLine("What is your favourite colour? ");
            var colour = ReadNonEmptyString();

            Console.WriteLine($"{name} is on a quest {quest} and his favourite colour is {colour}.");
        }
    }