Explicit move constructor needed in container?

Question

I have a templated container class:

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

I want to do

  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 move semantics, but Bag does not. Would mData in this case be moved or copied?

Answer 1

It would 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 as long as the user doesn't define his/her own :

• destructor
• copy constructor
• copy assignment
• move assignment

Since your class has none of these user defined constructors the compiler generated move constructor will be called, that constructor will move mData.