Re: [boost] An attempt to generalize the Pimpl idom with properly separated interface and implementation

From: Ulrich Eckhardt (doomster_at_[hidden])
Date: 2007-10-07 05:34:49

On Saturday 06 October 2007 23:10:52 Mathias Gaunard wrote:
> Vladimir Batov wrote:
> > shared_ptr is an extremely versatile and poweful gadget. One (among
> > others) thing it handles well is incomplete classes for implementation
> > hiding. Maybe there are other smart pointers doing that sort of thing
> > cheaper. I am not sure.
>
> Here is a simple deep-copying smart pointer.

Where from? I hope that one is not in productive use, because...

> template<typename T>
> struct copy_ptr
> {
[...]
>      explicit copy_ptr(T* ptr_) : ptr(ptr_)
>      {
>      }

...this should use std::auto_ptr to make clear that ownership is transferred 
and...

>      copy_ptr(const copy_ptr& p) ptr(p.ptr ? new(ptr) T(*p.ptr) : 0)
>      {
>      }
>
>      copy_ptr& operator=(const copy_ptr& p)
>      {
>          if(ptr)
>          {
>              if(p.ptr)
>              {
>                  *ptr = *p.ptr;
>              }
>              else
>              {
>                  delete ptr;
>                  ptr = 0;
>              }
>          }
>          else if(p.ptr)
>          {
>              new(ptr) T(*p.ptr);
>          }
>      }

...it looks like you are using placement new on a null pointer in the 
assignment and on an uninitialised pointer in the copy constructor, or am I 
missing something?

>      void swap(copy_ptr& p)
>      {
>          T* tmp = ptr;
>          ptr = p.ptr;
>          p.ptr = ptr;
>      }

How about
  std::swap( p.ptr, ptr);
?

>      T* operator->()
>      {
>          return ptr;
>      }
>
>      const T* operator->() const
>      {
>          return ptr;
>      }

Why? I mean since when is the CV qualification of a pointer relevant for the 
CV qualification of the pointee?

Uli