Assignment prevention?

[Duy3]

I noticed people put both operator= and dtor member functions in class private section to prevent copy at assignment.

For example:

http://en.wikipedia.org/wiki/Singleton_pattern#C.2B.2B

Could someone think of a scenario where assignment prevention is necessary (the operator= function). In my opinion, for singleton case, it is not; because hidding the dtor wont allow any "foreign" instances. No?

[kbw]

It doesn't make sense to copy some objects, like a factory class for example. In general manager classes tend not to be 'copyable'.

[jsmith]

But hiding the destructor means you can't destroy any instance of the class, even ones that
aren't copies.

The non-copyable pattern is to declare the copy constructor and assignment operator private
and leave them unimplemented.

Assignment and copy are very, very similar. Typically if you don't want copyability then
you don't want assignability either, and vice versa.