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

[Johannes Pfau]

Am Wed, 01 Aug 2018 16:04:01 -0700 schrieb Walter Bright:

> 
> Now, with D:
> 
>      extern (C++, ab) void foo(long);
>      foo(0);    // works!
>      ---
>      extern (C++, ab) void foo(long);
>      extern (C++, ab) void foo(int);   // error!
>      ---
>      extern (C++, ab) void foo(long);
>      extern (C++, cd) void foo(int);
>      foo(0);    // error!
> 
> I juxtaposed the lines so it's obvious. It's not so obvious when there's
> a thousand lines of code between each of those lines. It's even worse
> when foo(long) sends a birthday card to your daughter, and foo(int)
> launches nuclear missiles.

You probably didn't completely think this through: Earlier you suggested 
to use aliases to avoid explicitly specifying the c++ scopes. Then you 
suggested to use mixins or translator tools to automate alias generation 
and avoiding manually writing that boiler plate code. But if you do that:

-------------------------
extern (C++, ab) void foo(long);
extern (C++, cd) void foo(int);
alias foo = ab.foo;
alias foo = cd.foo;
-------------------------

You've now got exactly the same problem with hijacking...

So the benefit of explicit c++ namespace scoping is only a benefit if you 
do not use this alias trick. But then you face all other problems 
mentioned earlier...

As a result, everybody now has to use the aliasing trick, the hijacking 
problem still exists and we have to write lots of useless boilerplate.

-- 
Johannes