[C++-sig] Re: map key

[Mike Rovner]

"David Abrahams" <dave at boost-consulting.com> wrote in message
news:usmvrh0l3.fsf at boost-consulting.com...
> "Mike Rovner" <mike at bindkey.com> writes:
>
> <snip>
>
> Mike, lots of mailers don't respond well to indentation with tabs.

I'm sorry for the formatting. There was no tabs but something strange
happened with pasting from VC7.

> There is no function returning const Key* being invoked, but I see
> what you mean.  The problem occurs where you try to convert a ``const
> Key*'' to a Python object.

That's correct.

> > Can I specify return_internal_reference when constructing keys list?
>
> Hum, that's an interesting question.  I guess you'd like each of the
> items in the keys list to keep the map object alive so that they will
> remain valid.  You could use t.append(ptr(it->second)), which would
> build an object around the pointer and stick it in the list, but that
> would not have the desired lifetime-management properties.

It is working, but I still don't understand it. ;)
I have a map<const Key*, Value>, so map<>::iterator it->first shall
return const Key* or at least const Key* const&. So we already have a
pointer,
why we need a ptr() call around it?

I'd like to have a lifetime-management, but I'm still shallow on it.
I don't need to keep a map, because map keys are pointers to an object
elsewhere and
manupulating them can be a potential disaster but I'm limited by existing
library I'm wrapping. :(

But while it's great at hand-maid keys() and items() lists, there's still a
problem with
iterator<map<const Key*, Value> >(). Obviosly it doesn't know about ptr().

> One approach would be to wrap a function which could convert
> the pointer with the lifetime management you want:

I have a host object Host which holds all Keys and cleaning them on
desruction.
Host can return const Key* and I'd like to keep that (wrapped) host instead.

> I think that would solve it.

Thanks a lot, Dave. BPL already saved us a week debugging and more is on the
way.

> Mike, I think this would make a really good tutorial case study for
> the Boost.Python documentation.  Is there any way I could persuade you
> to write it up so that others can benefit?

(side note) I'm constantly adding some stuff from that list to the wiki.
OK, if you think I can do it, I can do it. :)
You mean that http://www.boost.org/libs/python/doc/tutorial/index.html
tutorial?
I need a few lines guidelines like a few questions that my future text will
answer
and I'll go for it.