[boost] Re: Formal Review: Circular Buffer

From: Pavel Vozenilek (pavel_vozenilek_at_[hidden])
Date: 2004-03-08 19:55:06

"David Abrahams" <dave_at_[hidden]> wrote

> I can't understand this claim.  If the counter works properly, then it
> will stay valid.
>
This example was too simplified (and thus not to the point).

More complex one:

-----------------------
struct  my_class
{
  void* database_handle;

  my_class() { database_handle = allocate_handle(); }
  ~my_class() { destroy_db_handle(database_handle); }
  my_class& operator=(const my_class& other) {
      // no copy of database handle, not needed,
      // not useful here
  }
  my_class(const my_class& other) {
     database_handle = allocate_handle(); // needs unique db connection
  }
};

circular_buffer<my_class> buffer(1);

{
  my_class a;
  buffer.push_back(a);  // 2 handles after function returns
  ...
}

{
   my_class b;
   buffer.push_back(b);  // desctructor not called, handle lost
   ...
}
-----------------

To deal with lost resources you would need to modify
operator=() to take ownership of  all rhs resources.
But in this case following will fail:

  my_class a;
  my_class b;
  a = b;
  // b is stripped of its handle now, cannot be used

/Pavel