public interface IValidatable
    {
        bool IsValid { get; }
        void Validate();
        // (more validation-related methods here...)
    }

    public class Validatable<T> : IValidatable
        where T : class
    {
        public Validatable(T obj)
        {
            Object = obj;
        }

        public T Object { get; private set; }

        public bool IsValid { get; set; }

        public void Validate()
        {

        }

        public static implicit operator Validatable<T>(T other)
        {
            return new Validatable<T>(other);
        }

        public static explicit operator T(Validatable<T> other)
        {
            return other.Object;
        }

    }

    public static class Validatable
    {
        public static IValidatable AsValidatable<T>(T obj)
            where T: class
        {
            if (obj == null)
                return null;

            var already = obj as IValidatable;

            return already ?? new Validatable<T>(obj);
        }
    }

    public class Person // not IValidatable
    {
        public string FirstName { get; set; }
        public string LastName { get; set; }
    }

public void ConversionTest()
    {
        var person = new Person { FirstName = "Bob", LastName = "Smith" };

        var validatable = Validatable.AsValidatable(person);

        var cast = (Person)validatable; // FAILS here with InvalidCastException
    }