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

[Jonathan M Davis]

On Sunday, July 29, 2018 2:28:08 AM MDT Walter Bright via Digitalmars-d 
wrote:
> On 7/29/2018 1:15 AM, Manu wrote:
> > All we're asking for is that C++ namespaces do **nothing** except affect
> > the mangling.
>
> If I do that, the next bug report will be:
>
>    extern (C++, "ab") { void foo(); }
>    extern (C++, "cd") { void foo(); } // Error, foo() is already declared
>
>    foo(); // which one gets called?
>
> The reason namespaces were added to C++ is to not have such name
> collisions. Namespaces in C++ introduce a scope. D cannot interoperate
> with this without introducing a scope as well.

I guess that the argument at that point is that you would have to put them
in separate D modules, just like you would if they were extern(D) functions.
If that were the only problem, then that doesn't sound like a big one -
especially if the documentation made it very clear that extern(C++)
declarations did not affect the lookup rules, thus forcing you to rely on
D's module system to deal with it all. All the extern(C++, NS) stuff does at
that point is to enable linking with C++ and forces all of the normal D
rules, which at least _sounds_ like it would be straightforward. If
anything, it seems like it would make things much simpler.

However, I've done nothing with C++ namespaces in D thus far. So, I really
can't comment on the problems beyond what I've read in threads like this
one.

- Jonathan M Davis