Re: Drawbacks of using declarations/namespace aliases

On 12/12/2012 03:22 PM, Lubos Lunak wrote:
> On Tuesday 11 of December 2012, Stephan Bergmann wrote:
> > > commit 3e64874e7cd234ff563ac11450cfb2b6e2db4bf6
> > > Author: Radu Ioan <ioan.radu.g@gmail.com>
> > > --- a/configmgr/source/access.hxx
> > > +++ b/configmgr/source/access.hxx
> > > @@ -82,7 +82,6 @@ namespace com { namespace sun { namespace star {
> > >        }
> > >        namespace util { struct ElementChange; }
> > >    } } }
> > > -namespace rtl { class OUString; }
> >
> > Changes like this are, strictly speaking, unsound.  They rely on at
> > least one of the included headers happening to in turn include
> > rtl/ustring.hxx.
>
>   Which, practically speaking, is pretty much guaranteed to happen for
> OUString.
>
> > The underlying intransparency wrt forward declarations is IMO a
> > fundamental drawback of the recent efforts of beautification via using
> > declarations or namespace aliases, for rtl and com::sun::star.
>
>   I don't understand what fundamental drawback you mean.

The drawback that you must either break transparency when using forward 
declarations (by explicitly mentioning "namespace rtl { ... }" resp. 
"namespace com { namespace sun { namespace star { ... } } }") or use 
#includes instead of forward declarations (which increases dependencies 
and thus needles recompilations; arguably not much of an issue for the 
rtl::OUString etc. case, but potentially an issue for the com::sun::star 
case).

Stephan