Re: Adding functions to generic package

[Matthew Heaney <matthewjheaney@earthlink.net>]

Marius Amado Alves <amado.alves@netcabo.pt> writes:

> > I guess it must be:
> >
> >    procedure Swap (Container : in out Container_Type; L,R :
> > Iterator_Type);
> >
> > as I want the Swap to Swap say element in position 4 with element in
> > postion 2 in the list but by using iterators to point at them.
> 
> No need. Cursors know their containers.

No, this is wrong.

In Charles, iterators do *not* carry a pointer to container (they only
hold a pointer to the node containing the element), and so (in Charles)
you'd need to pass the container too.

But moving a node can change the value of the head and foot pointers,
which are part of the representation of the container type, so you need
to pass the container anyway.  The rule is that whenever an operation
manipulates the container object itself, the container is passed a
parameter.

Mario is probably thinking of the Ada 2005 standard container library.
Cursor types do indeed hold a pointer to the container, in addition to
the node.  However, the rule about manipulation of the container object
still applies (what a coincidence!), so the container is passed as a
parameter too (see the operation named Swap_Links).

-Matt