Question

I have searched for hours for a solution and tried different methods to address my compilation errors related to unique_ptr and no copy/no assign. I even wrote a hidden copy and assign to prevent vector from calling it to no avail.

Here is the code causing the compilation errors:

class World{
    World(const World&) {}
    World& operator=(const World&) {return *this; }

    std::vector<std::vector<std::unique_ptr<Organism>>> cell_grid;
public:
    World() {
        cell_grid = std::vector<std::vector<std::unique_ptr<Organism>>> (20, std::vector<std::unique_ptr<Organism>> (20, nullptr));
    }
    ~World() {}
};

Compilation errors are related to the private member access issue.

Answer 1

The problem is the use of this vector constructor:

vector(size_type n, const T& value);

This constructor creates a vector of length n and each of the n elements has a copy of value. Since unique_ptr can not be copied (and neither can a vector<unique_ptr>), one can not use this constructor. Instead do this:

World()
    : cell_grid(20)
{
    for (auto& row : cell_grid)
        row.resize(20);
}

The first line calls the default constructor of vector<unique_ptr>, creating 20 size 0 vector<unique_ptr>s.

The loop then resizes each of those vector<unique_ptr>s to have size == 20, with each element being a default constructed unique_ptr (which will have the value nullptr).