some crazy stuff

gistfile1.cpp

        struct Node {

        };

        template<class T>
        struct ReadOnly {
            T* _val;
            friend class Writeable<T>;
        public:
            //ReadOnly(T& v) : _val(&v) {}
            //ReadOnly(Writeable<T>& v) : _val(v.readonly()) {}

            const T& value() const { assert(_val);  return *_val; }

            Writeable<T> writeable() {
                Writeable<T> v = { _val };
                _val = nullptr;
                return v;
            }
        };

        template<class T>
        struct Writeable {
            T* _val;
            friend class ReadOnly<T>;
        public:
            // Can't be constructed from 'const T&' !!!
            Writeable(T& v) : _val(v) {}
            //Writeable(ReadOnly<T>& v) : _val(v.writeable()) {}

            T& value() const { return *_val; }

            ReadOnly<T> readonly() {
                ReadOnly<T> v = { _val };
                _val = nullptr;
                return v;
            }
        };

        void doConst(ReadOnly<Node> n) {}
        void doMut(Writeable<Node> n) {}

        static Writeable<Node> findMatchingNode(Writeable<Node> root) {

            {
                doConst(root.readonly());

            }

            doMut(root);
        }