How to enforce move semantics when a vector grows?

Question

I have a std::vector of objects of a certain class A. The class is non-trivial and has copy constructors and move constructors defined.

Answer 1

It seems, that the only way (for C++17 and early), to enforce std::vector use move semantics on reallocation is deleting copy constructor :) . In this way it will use your move constructors or die trying, at compile time :).

There are many rules where std::vector MUST NOT use move constructor on reallocation, but nothing about where it MUST USE it.

template
class move_only : public T{
public:
   move_only(){}
   move_only(const move_only&) = delete;
   move_only(move_only&&) noexcept {};
   ~move_only() noexcept {};

   using T::T;   
};

Live

or

template
struct move_only{
   T value;

   template&&, Arg >
            && !std::is_same_v&, Arg >
    >>
   move_only(Arg&& arg, Args&&... args)
      :value(std::forward(arg), std::forward(args)...)
   {}

   move_only(){}
   move_only(const move_only&) = delete;   
   move_only(move_only&& other) noexcept : value(std::move(other.value)) {};    
   ~move_only() noexcept {};   
};

Live code

Your T class must have noexcept move constructor/assigment operator and noexcept destructor. Otherwise you'll get compilation error.

std::vector> vec;