Re: GCC 4.0 Ada.Containers Cursor danger.

["Matthew Heaney" <mheaney@on2.com>]

Maxim Reznik wrote:
>
> I mean it should be avoided by Ada (by standard), not by the user.

This is completely wrong.  You have no business legislating behavior
for everyone else.

This reminds me of our laws here in the US during the time of
prohibition.  These little old ladies complained that "We don't drink,
and we don't want anyone else to drink either," and so the sale of
alcohol was made illegal.  Well that's ridiculous.  If you yourself
choose not to consume alcohol, then that is your own business.  You
have no right to take away someone else's freedoms.

(Thankfully the laws against the sale of alcohol were repealed.  It's
still a sorry state of affairs here, however, since we still have laws
criminalizing the use of other recreational drugs such as marijuana,
which has only created a huge, billion-dollar black market.  So much
for our belief in limited government and free market capitalism.  But I
digress...)

The point is that you should only worry about your own behavior.  If
other developers make choices different from you, then those are their
choices.  Stop worrying about everyone else.


> If make container remember all its cursors we can implement
> all operations which make cursors invalid so that they
> reset invalid cursors to No_Element.

If you want that abstraction, then you can write it yourself.  That's
what freedom means.


> For instance, Remove will iterate over all cursors for
> the container, check target of cursor and set cursor to
> No_Element if target match removed element.

Fine, then you can implement the Remove operation of your container
abstraction that way.  You have complete freedom to do so.


> The method I propose costs O(cursors per container) performance
> penalty. I think it's acceptable cost for safety.

Fine, then you have the freedom to implement such an abstraction.


> If we should choise between safe and good performance
> Ada containers I would choose safe ones.

Fine, then that's your choice.  Why are you so obsessed with what
everyone else does?


> In rare cases when user encounter performace limits he
> could easy implement his own container, with limited functionality.
> And he will know exactly where dangling references could apear.

Yes, and that user is you.  You have the freedom to implement such a
container.


> Now cursor is like grenade. You don't know what happens if you
> use it.

The solution is simple: don't use cursors.  You have that freedom.

-Matt