opencxx-users

[Opencxx-users] symbol lookup

[Stefan S. <se...@sy...>]

hi there,

as far as I understand, symbol lookup in opencxx works by traversing a linked list
of 'Environment' objects. However, the C++ lookup rules seem to suggest at least
a tree, if not a (directed acyclic) graph. Just think about multiple inheritance
as the most obvious example.

Am I missing something ? Does symbol lookup currently work in such cases ?

Thanks,
		Stefan

Re: [Opencxx-users] symbol lookup

[Grzegorz J. <ja...@ac...>]

Hi!

Stefan Seefeld wrote:
> as far as I understand, symbol lookup in opencxx works by traversing a 
> linked list
> of 'Environment' objects. However, the C++ lookup rules seem to suggest 
> at least
> a tree, if not a (directed acyclic) graph. Just think about multiple 
> inheritance
> as the most obvious example.
> 
> Am I missing something ? 

I don't pretend to understand all the details of how it works, but I 
think there is more to it than you describe. Look at 
'SearchBaseOrUsing()', which to my understanding handles the 'forks' in 
the acyclic graph.

Also note that OpenC++ is non-validating, consequently it rightfully 
ignores, say, ambiguities in multiple inheritance.

On the other hand, lookup implementation is missing several features 
(e.g. ADL).

> Does symbol lookup currently work in such cases ?

Why not check empirically?... :-)

Best regards
Grzegorz

Re: [Opencxx-users] symbol lookup

[Stefan S. <se...@sy...>]

Grzegorz Jakacki wrote:

> I don't pretend to understand all the details of how it works, but I 
> think there is more to it than you describe. Look at 
> 'SearchBaseOrUsing()', which to my understanding handles the 'forks' in 
> the acyclic graph.

you are right. I was puzzled by the 'GetOuterEnvironment()' call...

However, I must admit that I don't quite like the current design.
As different context require different loopup rules, an IMO better
approach would have been to provide a polymorphic 'Scope' type
and then implement it differently for 'Function', 'Class', 'TemplateClass',
etc. Then each scope would know the rules of where to look if a symbol
isn't defined locally. This would be more flexible and in particular
allow to implement different lookup semantics depending on whether
we are parsing C++ or C. What do you think ?

> Also note that OpenC++ is non-validating, consequently it rightfully 
> ignores, say, ambiguities in multiple inheritance.

yeah, I notice that the current implementation isn't complete.

>> Does symbol lookup currently work in such cases ?
> 
> 
> Why not check empirically?... :-)

heh, right. That brings me back to the other point: unit testing.
Now that the release is out (congratulations !) we should try to
cover as much as possible with unit tests so we can a) make sure
changes don't incure regressions and b) learn how occ works in detail.

Regards,
		Stefan