Re: struct environment

[Daniel Jacobowitz <drow at mvista dot com>]

On Tue, Sep 17, 2002 at 03:52:33PM -0400, Daniel Berlin wrote:
> 
> On Tuesday, September 17, 2002, at 02:02  PM, Daniel Jacobowitz wrote:
> 
> >On Tue, Sep 17, 2002 at 01:54:07PM -0400, Andrew Cagney wrote:
> >>>Well, sort of.  It won't be a DAG necessarily (I think that mutual
> >>>>>"using" statements are legal in C++; I remember a GCC bug involving
> >>>>>them was fixed not long ago), and it will be somewhat complicated
> >>>>>figuring out which ones to look up (namespace links are different 
> >>>>>than
> >>>>>block scope links).
> >>>
> >>>>
> >>>>Don't forget that GDB doesn't need to model the language.  Just the
> >>>>namespace behavior at a given PC.  The effect of "using" would be to
> >>>>just grow a nametab in someway.
> >>>
> >>>
> >>>This is legal C++:
> >>>
> >>>namespace D {}
> >>>
> >>>namespace C {
> >>> using namespace D;
> >>> int x, y;
> >>>}
> >>>
> >>>namespace D {
> >>> using namespace C;
> >>> int x, z;
> >>>}
> >>>
> >>>If using just grew a nametab we'd get into a great deal of trouble.
> >>
> >>Depends on how you grow it :-)  Something like (assuming a real 
> >>language
> >>:-):
> >>	D:
> >>	0: x, z
> >>	1: x, y (from C)
> >>	2: ...
> >
> >How you intend to do this efficiently I don't know.  Remember that C
> >uses D in turn, and that things "using"'d into D will therefore be
> >visible in C.
> 
> These types of problems are exactly why i said a lot of thought needs 
> to be put into the design of the underlying structures, rather than 
> just copying what we have because we have it.
> It's hard to call it "overengineered" if how to do lookups efficiently 
> with large numbers of names in namespaces hasn't been considered.
> It's not really something you can bolt on later.
> Hasn't this been proven by the fact that it hasn't been bolted on yet?

Absolutely.  But I've always thought that we'd still do it via
searching a succession of blocks, with some sort of global structure
for figuring out where to look; which means that at this point it's
been designed far enough.  I could be wrong :)

-- 
Daniel Jacobowitz
MontaVista Software                         Debian GNU/Linux Developer