Question

I have a class TileManager that manages the lifetime of objects and therefore holds a shared_ptr on them:

class TileManager {
private:
    std::vector<std::shared_ptr<const Tile>> tiles;
}

Now I have another class Map which holds non-owning references to the objects managed by TileManager:

class Map {
private:
    std::vector<std::weak_ptr<const Tile>> tiles;
}

My problem is: I don’t want the Map class to be able to manipulate the smart pointers to Tile. Therefore I would like to make the pointers inside the vector const:

class Map {
private:
    std::vector<const std::weak_ptr<const Tile>> tiles;
}

Unfortunately it is not possible to put const objects into a STL container.

Anyone know a solution? Maybe a completely different design?

Answer 1

Elements stored in a vector cannot be const because they must be assignable. The only way that the vector could “manipulate” the pointers in any observable way would be to destroy the last weak_ptr to a given object which would cause the control block for the corresponding shared_ptr to be deallocated (assuming there are no other shared_ptr‘s that still reference it).

In short, you can safely store non-const weak_ptr‘s in a vector.