Re: GCC 4.0 Ada.Containers Cursor danger.

[Matthew Heaney <matthewjheaney@earthlink.net>]

Mikhail Terekhov <terekhov@emc.com> writes:

> > Yes, but in your original example, you were complaining about a
> > run-time error.  That error is detectable.
> 
> Not using this special case abstraction (Cursor) in general part of
> the library would exclude this kind of errors completely.

But if you recall, the original example used Replace_Element to replace
the element designated by a (dangling) cursor.  The OP played with fire
and he got burned.  If you want to produce the same effect sans cursors,
then just use Include (which is key-based).


> Great, to satisfy a common need, users should build a layer on top of
> such a "general library".

The common need is satisfied by other, key-based operations such as
Include and Replace.



> > You want to legislate behavior for everyone.  This is wrong.  You
> > should only be concerned with your own behavior.
> 
> I unerstand this as "shut up and go away". This is not polite. Try to
> apply the above three sentences to yourself.

It simply reflects the realities of library design.  The designer must
strike a balance among flexibility, efficiency, and safety, and those
goals are often in conflict.


> > If you want only key-based operations, then you can just write a
> > layered abstraction once, and you can use it everywhere.
> >
> That means do it youself. So much for a "generic" library - if you need
> some generic case - do it yourself.

Again, the library is optimized for flexibility and efficiency.  You're
advocating an interface that is less general, less flexible, and less
efficient, so you have the burden of proving why that's better.  Saying
that "cursors don't make sense" is not a very convincing argument.