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From: Thorsten Ottosen (nesotto_at_[hidden])
Date: 2004-12-10 18:28:34

"Eelis van der Weegen" <eelis_at_[hidden]> wrote in message
| Two issues:
| (1.) I stumbled upon a strange inconsistency in boost::ptr_map's
| iterator interface. I've attached some demonstration code that shows the
| problem.

As for the code, then I think you are right. Had you written const_iterator
and not const iterator, I would expect differently. So this is an error in my

| (2.) Given a (nonempty) const std::map<X, Y*> object, it is possible to
| retrieve a Y& from it. Given a const boost::ptr_map<X, Y> object, it is
| not possible (without casting) to retrieve a Y& from it.

yes. but that cast is a bad idea; add const the right places instead.

| Thus, it is not possible (in general) to refactor code which uses a
| std::map<X, Y*> combined with manual ptr_map-like lifetime/ownership
| management to use a boost::ptr_map<X, Y> without changing const semantics.
| Was this effect intentional?

yes. All the containers propagate constness.

| If so, why was this approach chosen?

to make it easier to write const-correct programs.

there has been discussion about this from time to time, but in general my
impression has been than propagation of constness was appropriate for
non-shared resources.

| It seems like ptr_map attempts to "hide" the level of indirection that a
| standard container of pointers has.

yes, some have suggested to call them indirect containers instead.

| While this may be desirable, I think
| it should be mentioned in the documentation since it can come as a
| surprise to people (like me) who actually try to perform the refactoring
| mentioned above.

yes, it will be mentioned (if it isn't all ready).



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