Csdrhrt

In order to make an object non-copiable we can explicitly delete both its copy-constructor and copy-assignment operator.

My question is: What is the right place to do it - in the public, private or protected section of the class? And - does this choice make any difference?

what is the right place to do it - in the public, private or protected section of the class?

I would put them in the public section.

This is because deleting a constructor or an assignment operator is orthogonal to making them private / protected; and when these aren't deleted, they are public. Putting the deletions in one of those two sections seems to me like hinting "If I hadn't deleted them, I would have made them private/protected" - which is not a message you want to convey in your case.

Note, though, that the compiler doesn't care which section you put the deletion in.

Does where we put the deleted definition make any difference?

From a pure language standpoint it makes absolutely zero difference. Name lookup and overload resolution happen before access checking. And attempting to refer to a deleted function at the end of overload resolution makes your program ill-formed, period. A compiler may or may not issue another diagnostic about the accessibility, but the program already has an error that must be reported.

So you can put that deleted definition with whatever accessibility you desire. I think most will keep it private, to be inline with the "old" practice of making a class non-copyable (put the declaration of those members in the private section of the class, and not define them), if only to help those who know the old ways "get it" sooner. A mixture of idioms, if you would.

Marking as private is also something you can't avoid if you need to support both C++03 and C++11 mode. With the help of a macro, a header can be made to conform to both standards easily:

#if __cplusplus >= 201103L

  #define DELETED_DEFINITION = delete

#else

  #define DELETED_DEFINITION

#endif



class noncopyable {

private:

  // This header can be compiled as both C++11 and C++03

  noncopyable(noncopyable const&) DELETED_DEFINITION;

  void operator=(noncopyable const&) DELETED_DEFINITION;

};

From Scott Meyers's book, Effective Modern C++ (Item 10), it seems that it is better to define them as public:

By convention, deleted functions are declared public, not private.
There’s a reason for that. When client code tries to use a member
function, C++ checks accessibility before deleted status. When client
code tries to use a deleted private function, some compilers complain
only about the function being private, even though the function’s
accessibility doesn’t really affect whether it can be used. It’s worth
bearing this in mind when revising legacy code to replace
private-and-not-defined member functions with deleted ones, because
making the new functions public will generally result in better error
messages.

In addition, I believe that a deleted copy constructor/assignment, should be part of the class interface to be shared with ALL of the class users. Such kind of information should not be kept as secret by making them private.