Class MovableObject

tests/test_callbacks.cpp:210–222

          [](const std::function<double(AbstractBase &)> &) {});

    struct MovableObject {
        bool valid = true;

        MovableObject() = default;
        MovableObject(const MovableObject &) = default;
        MovableObject &operator=(const MovableObject &) = default;
        MovableObject(MovableObject &&o) noexcept : valid(o.valid) { o.valid = false; }
        MovableObject &operator=(MovableObject &&o) noexcept {
            valid = o.valid;
            o.valid = false;
            return *this;
        }
    };
    py::class_<MovableObject>(m, "MovableObject");

    // test_movable_object