Why does the insertion of user defined destructor require an user defined copy constructor

Question

The following code compiles:

#include 
#include 
#include 

using namespace std;

class container
{
public:
    conta         


        

Answer 1

The code gets compiled because buildShip() would use the move constructor automatically generated by the compiler when returning tmp. Adding user-declared destructor prevents the compiler from auto-generating one. E.g., see this or this questions. And the compiler-generated copy constructor can not be used because of the member up which is std::unique_ptr. And copy constuctor of unique_ptr is explicitly deleted.

So this will compile, because the compiler is explicitly asked to generate the move constructor:

class Ship
{
public:
    Ship(){}
    Ship(Ship&&) = default;
    ~Ship(){}
    std::unique_ptr up;
};