Re: GCC 4.0 Ada.Containers Cursor danger.

[Matthew Heaney <matthewjheaney@earthlink.net>]

"Dmitry A. Kazakov" <mailbox@dmitry-kazakov.de> writes:

> Think about differences between:
> 
> - An unordered set of unordered elements

Does not exist in the Ada 2005 standard container library.


> - An unordered set of ordered elements

Does not exist in the Ada 2005 standard container library.


> - An ordered set of unordered elements

The Ada 2005 standard container library calls that a "hashed set."


> - An ordered set of ordered elements (and these orders are different)

The Ada 2005 standard container library calls that an "ordered set."


> Hmm, what about ring buffers?

Does not exist in the Ada 2005 standard container library.


> And for proofs it is essential that the premises were correct. Programming
> is not much different...

Yes, that's called a "reference manual."


> > I find Cursors useful when I want to put an index set into
> > operations inside a computer. When I'm can use any container, how
> > could I implement index sets without Cursors?
> 
> You are mixing implementation and interface.

Of course a container must "mix implementation and interface," since it
has to provide access to its elements.  The essential container design
problem is doing that without exposing representation details.  Cursors
are that mechanism.

There's nothing bad about this; it's simply the nature of a container
abstraction.  The container should get out of the way as much as
possible, since it's the elements we care about.


> [and again, sets could be searchable and not]

The sets in the Ada 2005 standard container library are searchable.