Is there any good reason why C++ namespaces are "closed" in D?

[Manu]

On Wed, 1 Aug 2018 at 10:25, Jonathan M Davis via Digitalmars-d
<digitalmars-d at puremagic.com> wrote:
>
> On Wednesday, August 1, 2018 4:02:39 AM MDT Walter Bright via Digitalmars-d
> wrote:
> > On 7/31/2018 1:12 AM, Manu wrote:
> > > Given your favourite example:
> > > ----
> > > module a;
> > > extern(C++, ns) void foo();
> > > ----
> > > module b;
> > > extern(C++, ns) void foo();
> > > -----
> > > module c;
> > > import a, b;
> > > foo(); // error: ambiguous
> > > ns.foo(); // error, ambiguous (obviously)
> > > a.ns.foo(); // naturally, this works... it's the D module that
> > > correctly organises the symbol. 'ns' is worthless here
> >
> > You can write it like this:
> >
> > ----
> > module a;
> > extern(C++, ns) void foo();
> > alias foo = ns.foo;
> > ----
> > module b;
> > extern(C++, ns) void foo();
> > alias foo = ns.foo;
> > -----
> >
> > import a,b;
> > a.foo();  // calls a.ns.foo()
> > b.foo();  // calls b.ns.foo()
>
> Not to say that that can't work, but I have to say that it seems pretty ugly
> if using extern(C++, NS) requires a bunch of aliases just to use symbols
> normally. If the namespace were just part of the mangling, none of those
> aliases would be necessary. All in all, it just seems like having the
> namespaces add scoping just gets in the way - especially when they would
> normally get the necessary scoping from being put into separate D modules.
>
> Reading through this thread, and thinking about the issue, I don't see any
> advantage to the current behavior over having it just affect mangling other
> than the fact that that's how it currently works. All of the potential
> complaints that you talk about seem like they at least _should_ be a
> non-issue given that folks don't complain that way about D's module system
> for non-C++ functions - but it's certainly true that even engineers aren't
> always logical or reasonable.
>
> However, if we were discussing a DIP for implementing namespaces for C++,
> based on my current understanding of the matter, I'd definitely argue that
> extern(C++) with namespaces should just affect mangling, since that approach
> seems much more straightforward and much more in line with how other
> languages are handled, particularly since the scoping aspect is already
> going to be handled by D's module system anyway. As it stands, it just seems
> like the language is forcing that all C++ functions be put inside of structs
> to namespace them on top of them being put into a module. And that's
> downright awkward, even if it can work. Certainly, it does come across like
> you didn't trust the D module system to do its job for some reason.

Thank you Jonathan.