Explicit move constructor needed in container?

Question

I have a template container class:

template<class Stuff> class Bag{ private: std::vector<Stuff> mData; }; 

I want to make

  void InPlace(Bag<Array>& Left){ Bag<Array> temp; Transform(Left, temp); //fills temp with desirable output Left = std::move(temp); } 

Suppose Array has user-defined movement semantics, but Bag does not. Will mData move or copy in this case?

Answer 1

It will be moved, not copied.

I would suggest looking at the following image:

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This clearly shows that the compiler implicitly generates a move constructor if the user does not define his / her own:

• destructor
• copy constructor
• copy assignment
• move destination

Since your class does not have any of these user-defined constructors, the constructor generated by the compiler will be called, this constructor will be moved by mData .