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

[Walter Bright via Digitalmars-d]

On 8/3/2018 3:58 AM, Atila Neves wrote:
With your mixin template technique everything ends up in the global namespace of 
the moduel making the C++ declarations.

Right, but that's what you wanted!

I would only be able to alias a nested 
namespace once, since the code below obviously won't work:

    mixin CppNamespace0!() x;
    alias chrono = x.std.chrono;
    mixin CppNamespace1!() y;
    alias chrono = y.std.chrono;

Try this:


     mixin template X() {         // boilerplate prefix

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

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



I considered for a while whether or not this would be truly bad, and the more I 
think about it the more convinced I am that Manu is right and there should be 
_no_ scoping whatsoever in D regarding C++ namespaces. We have packages and 
modules, we can use those to put the C++ functions we declare in whatever 
hierarchy we want.

I am puzzled. With:

  namespace std {
     namespace chrono {
         void foo();
     }
  }

  namespace std {
    namespace chrono {
         void bar();
    }
  }

you have stated that it is impractical for your translator to rewrite this as:

   namespace std {
     namespace chrono {
         void foo();
         void bar();
     }
  }

Ok, I get that. But it is practical to rewrite it as:

   module std.chrono;
   void foo();
   void bar();

?

> I mean `std` should never be part of the fully qualified name of, for
> instance, `core.stdcpp.exception.std.bad_exception`. It should just
> be `core.stdcpp.exception.bad_exception` instead.

C++ recognizes that, too, which is why it has "using" declarations. D has the 
equivalent thing, "alias".

You can do things like:

    import std = core.stdcpp.exception;

and then refer to:

    std.bad_exception

or:

    import exception = core.stdcpp.exception;

    exception.bad_exception;

or whatever works best for one's project. Aliasing and import renaming (which 
are really just more aliasing) is very capable, and was designed for just these 
sorts of issues.