public class Usage
        {
            public Usage()
            {
                var foo = new Foo();
                var count = foo.Accept(new CountVisitor());
                var name = foo.Accept(new NameVisitor());

                var barCount = new Bar().Accept(new CountVisitor());
                var barName = new Bar().Accept(new NameVisitor()); // doesn't work cuz Bar is not IVisitable<string> = can't accept IVisitor<string>
            }
        }

        public class Foo : IVisitable<int, Foo>, IVisitable<string, Foo>
        {
            public int Accept(IVisitor<int, Foo> visitor) => visitor.Visit(this);
            public string Accept(IVisitor<string, Foo> visitor) => visitor.Visit(this);
        }

        public class Bar : IVisitable<int, Bar>
        {
            public int Accept(IVisitor<int, Bar> visitor) => visitor.Visit(this);
        }

        public class CountVisitor : IVisitor<int, Foo>, IVisitor<int, Bar>
        {
            public int Visit(Foo visitable) => 42;
            public int Visit(Bar visitable) => 32;
        }

        public class NameVisitor : IVisitor<string, Foo>
        {
            public string Visit(Foo visitable) => "yolo";
        }

        public interface IVisitable<TResult, out TVisitable> where TVisitable : IVisitable<TResult, TVisitable>
        {
            TResult Accept(IVisitor<TResult, TVisitable> visitor);
        }

        public interface IVisitor<out TResult, in TVisitable> where TVisitable : IVisitable<TResult, TVisitable>
        {
            TResult Visit(TVisitable visitable);
        }