hide auto generated assignement operator and copy constructor without replacing them

Question

I want to publicly hide the copy constructor and the assignment operator.

Furthermore i want to provide a clone().

Is it possible to just mark the copy constructor and the assignment operator as protected or private and use them in the clone function?

Maybe some kind of using clause.

The reason is that the class contains some data and a unique id that should be incremented with every instance. So making a copy would be using the default assignment operator and then change the id. I would like to circumvent the need to copy every member by hand to avoid forgetting to add one if a member was added to class.

πάντα ῥεῖ · Answer 1 · 2016-02-01T18:18:54.740

3

You can do:

class MyClass {
      MyClass(const MyClass&) = default;
      MyClass& operator=(const MyClass&) = default;
};

edited Feb 01 '16 at 18:18

answered Feb 01 '16 at 13:33

πάντα ῥεῖ

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at least since C++11 – king_nak Feb 01 '16 at 13:33
it seems that my compiler i am bound to, does not understand this aspect of c++11 :-( – vlad_tepesch Feb 01 '16 at 13:35
1

`MyClass()` is not an assignment operator. – IInspectable Feb 01 '16 at 13:42
@IInspectable Better? – πάντα ῥεῖ Feb 01 '16 at 13:45
Sort of. The OP didn't want to hide the default c'tor. Is there a particular reason you did? – IInspectable Feb 01 '16 at 18:17
@πάνταῥεῖ by declaring a construcor (in this case the copy constructor) the default one is removed anyway, is not? To not hide it you have to put it explicitly into public again. – vlad_tepesch Feb 02 '16 at 10:28
@vlad_tepesch As mentioned by others, introducing the default implementations is tantamount to introducing user defined constructors and assignment operations. There won't be a compiler generated default constructor. But you can again create a public default constructor with the same technique as used in my example. – πάντα ῥεῖ Feb 02 '16 at 10:58

score 1 · Answer 2 · edited Feb 01 '16 at 21:55

Since the answer of πάντα ῥεῖ would be the most favorable if c++11 is available I solved the problem by using a CRTP object counter that manages the id.

This class implements the counter and re-implements the copy c'tor and assignment operator so that the default ones of the child class can be created and used without danger.

template <class T>
class UidProvider
{
public:
  UidProvider()
  {m_id = getNewUId();}

  UidProvider(const UidProvider&)
  {m_id = getNewUId();}

  UidProvider& operator= (const UidProvider&)
  {m_id = getNewUId();}

  uint32 id()
  {return m_id;}

private:
  uint32 m_id;

  static uint32 getNewUId(){ return ++sm_id;}
  static uint32 sm_id;
};

class MyClass : public UidProvider<MyClass >{
 // ...
}

// in cpp
uint32 UidProvider<MyClass >::sm_id = 0;

score 0 · Answer 3 · answered Feb 01 '16 at 13:55

hide auto generated assignement operator and copy constructor without replacing them

To be pedantic, not possible.

In c++03 absolutely not possible.

In c++11, defining them as =default is technically providing a user-defined assignment operator and copy constructor, it's just that you're replacing them with the same functions that the compiler would implicitly generate. This will have the same effects as writing them explicitly - i.e. preventing the auto-generation of a move-assignment and a move-constructor.

hide auto generated assignement operator and copy constructor without replacing them

3 Answers3