extern(C++, ns)

[Walter Bright via Digitalmars-d]

On 1/17/2016 3:55 AM, Daniel Murphy wrote:
> So now we have two public symbols called 'mylib', and because they conflict they
> can't be used to disambiguate eg 'someotherlib.funca' with 'library.a.funca'.

Consider these two C++ files:

------file 1-------------
namespace (X) { int fooa() { ... }
------file 2-------------
namespace (X) { int fooa() { ... }
-------------------------

You'll get a multiply defined symbol error for X.fooa() from the linker. When 
using namespaces in D, the "one definition rule" needs to be followed just as in 
C++ for the same reason.

However, in D, you CAN do the following:

-----module M-----------
extern (C++,X) { int fooa(); }
-----module N-----------
extern  (C++,X) { int fooa(); }
------------------------

and yes, M.X.fooa() will wind up referring to the same externally defined symbol 
X::fooa() as N.X.fooa().

Because, as I said multiple times, namespaces in D affect the name mangling in a 
C++ way while doing symbol lookup in the D way.

Note that

    extern(C) { ... }

in D works EXACTLY the same way.