template<typename A>
class Lazy {
    private:
        A thing;
        bool haveThing;
        std::function<A> getTheA;
    template<typename FunctionReturningA>
    public:
        Lazy(FunctionReturningA f) : getTheA(f), haveThing(false) {}
        A *get() {
            if (haveThing) {
                return &thing;
            } else {
                thing = getTheA();
                haveThing = true;
                return &thing;
            }
        }
}