moving_unique_ptr.cpp

class A {};

// Proof of concept.
//
// A class that wraps a unique_ptr and creates a copy constructor that
// allows you to copy it without the explicit move constructor.
// The move constructor will be implied. This violates the expectation
// that copying a value is free of side effects and you should therefore
// probably not use this class.
template <class T> struct moving_unique_ptr {
  moving_unique_ptr(std::unique_ptr<T> _p) : p(move(_p)) { }

  moving_unique_ptr(const moving_unique_ptr &other) {
    this->p = std::move(const_cast<moving_unique_ptr &>(other).p);
  }
private:
  std::unique_ptr<T> p;
};

moving_unique_ptr<A> f() { return moving_unique_ptr<A>(std::make_unique<A>()); }

void g(moving_unique_ptr<A> a) {}

int main() {
  // this works automatically
  g(f());
  moving_unique_ptr<A> a = f();
  // this needs a move
  g(a);
}