Proposal: class nonallocatable

From: Jeffrey D. Paquette (paquette_at_[hidden])
Date: 2000-04-29 08:06:11

I've been following this group for a few months now and have seen several
variations of scoped utility classes fly by (shared_ptr, deferred_value,
etc) and it seems that all of these classes, including a few that I've
written have one drawback that can lead to misuse: they all can be
dynamically allocated, thus bypassing the intent of the class.

So, in the spirit of noncopyable, here is a first cut at nonallocatable:

class nonallocatable {
private:
  // single instance new and delete
  void *operator new(size_t);
  void operator delete(void *);
  void *operator new(size_t, const std::nothrow_t&) throw ();
  void operator delete(void *, const std::nothrow_t&) throw ();
  // array new and delete
  void *operator new[](size_t);
  void operator delete[](void *);
  void *operator new[](size_t, const std::nothrow_t&) throw ();
  void operator delete[](void *, const std::nothrow_t&) throw ();
  // placement new and delete
  void *operator new(size_t, void *) throw ();
  void operator delete(void *, void *) throw ();
  void *operator new[](size_t, void *) throw ();
  void operator delete[](void *, void *) throw ();
};

The idea is to derive scope-helper classes from nonallocatable, thus
preventing the misuse of these classes, like so:

void leak()
{
  shared_ptr<int>  *p = new shared_ptr<int>(new int);
}

test code:
class test : private nonallocatable {
public:
  int x;
};

class test2 : test {
};

int main (int, char **)
{
  test *p = new test;
  test2 *p1= new test2;
  test *p2 = new test[4];

  int q;
  test *p3 = new(&q) test;
  test2 *p4 = new(std::nothrow) test2;
  return 0;
}

Tested with VC6.0sp3 and egcs-2.91.66 (Redhat6.1)

I'm sure I'm going to get educated here :)

--
Jeff Paquette
paquette_at_[hidden], paquette_at_[hidden]
http://www.atnetsend.net