Question

I think I do understand “the basic IDEA” of move semantics, but now when I’m on the stage of implementing my own map I stopped and started to think about it when I was going to write a use case and walk through for move ctor of map. Correct me if I’m wrong but what I do understand how the whole business of move semantics works is that they suppose to help in avoiding unnecessary copying? Right? Now, take a map for example and just for the purpouse of this example assume that my map is modeled as:

class Map
{
Link* impl_;//THIS IS A POINTER TO A LINK WHICH HAS A parent, left and right (of Link type)
Map(Map&& tmp);//move ctor
//unnecessary code ommited
};

And here is the snag:
When I’m trying to think of move ctor for my map I cannot see a way of avoiding allocating a new space for all those links which needs to be created and then their pointers swapped with those from a tmp Map object (passed as a arg to my move ctor).
So I do have to allocate space anyway, or don’t I?

Answer 1

All you have to do is reassign the Link pointer, since all the other Link pointers are attached to it, they will now be part of the new Map.

Map(Map&& tmp) :impl_(tmp.impl_) { tmp.impl_ = nullptr; }

This is assuming no other data members.