extern(C++, ns)

[Marc Schütz via Digitalmars-d]

On Sunday, 3 January 2016 at 16:18:13 UTC, Walter Bright wrote:
> No. If D is to support C++ namespaces, it has to support 
> declaring the same identifier for different purposes in 
> different namespaces. C++ namespaces have different scopes in 
> C++. Doing anything else would make it impossible to connect to 
> perfectly legitimate C++ programs. The WHOLE POINT of C++ 
> namespaces is to support declaring the same identifier in 
> different namespaces.

Yes, but the point of `extern(C++, ns)` is NOT to achieve the 
same in D! D has its own mechanisms for that, primarily the 
module system, as well as hacks like static structs. And I don't 
see how Manu's suggestion would make it impossible to link to 
some C++ programs. Can you give an example?

>
>
>> This would solve a lot of awkward issues.
>
> It'd be a river of bug reports, because sure as shootin', 
> people are going to try to interface to this C++ code:
>
>   namespace ns1 { int identifier; }
>   namespace ns2 { int identifier; }
>
> And why shouldn't they? It's correct and legitimate C++ code.

I guess in reality this would not be a frequent thing. Most real 
C++ code will have both instances of `identifier` declared in 
different header files, and D's modules will usually closely 
mirror those, so they will end up in different modules on the D 
side.

In the rare case the same identifier actually does appear twice 
in the same module, static structs can be used:

struct ns1 {
     extern(C++, ns1):
     int identifier;
}
struct ns2 {
     extern(C++, ns2):
     int identifier;
}