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

[Walter Bright]

On 7/31/2018 1:47 AM, Atila Neves wrote:
> The only good way (I don't think the mixin template and struct solutions count) 
> to link to any of that today would be to have one enormous D file with 
> _everything_ in it, including nested namespaces.

Why doesn't it count? The user doesn't need to write that code, the translator 
does. It achieves what you ask for - a declaration of foo() in the current 
scope, with the mangling in the C++ namespace.

All it requires from the translator is putting a boilerplate prefix and suffix 
onto what it already does.

I.e.,

      extern (C++, ns) int foo();

becomes:

      mixin template X() {         // boilerplate prefix

          extern (C++, ns) int foo();   // original line

      } mixin X!() x; alias foo = x.ns.foo;  // boilerplate suffix

Of course, you'd also need to write X and x as X with __LINE__ appended so 
unique symbols are generated. (I know you've had trouble with generating unique 
names in another post, but that's an independent problem we should find a way to 
fix. Maybe instead of __LINE__, use a checksum of the original line?)