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

[Manu]

On Fri., 27 Jul. 2018, 10:30 am Atila Neves via Digitalmars-d, <
digitalmars-d at puremagic.com> wrote:

> I understand that being able to "reopen" namespaces in C++ is
> contentious - anybody can add to the `std` namespace in their own
> code. D doesn't have anything like it, and instead has packages
> and modules. So far, so good.
>
> But why does this not compile?
>
> extern(C++, ns) { void foo(); }
> extern(C++, ns) { void bar(); }
>
> I could maybe understand the limitation if those functions had
> bodies since we'd be importing the namespace functionality from
> C++ in a sense (and even then I'm not sure it's a big enough
> deal). But all I'm trying to do here is tell the D compiler how
> to mangle symbols.
>
> Why would this matter? Imagine a project that parses C++ headers
> and translates them to D declarations. Imagine that project is
> trying to parse `#include <vector>`. There will be many, many
> instances of `namespace std` in there, but such a
> not-so-hypothetical program can't just go through them and open
> and close `extern(C++, std)` as it goes along. Such a program can
> easily do that to `extern(C)`, but doing that to `extern(C++)` is
> for some reason not allowed.
>
> (is there even any semantic difference? extern(C) for a 2nd time
> is just reopening the global namespace!)
>
> One could simply manually `pragma(mangle)` everything up the
> wazoo, but unfortunately that doesn't work for templates, which,
> as it turns out, is pretty much everything inside the `std`
> namespace.
>
> My only solution is to keep track of all namespaces at all times
> and then sort the declarations by namespace, which:
>
> 1) Is incredibly tedious
> 2) Might cause problems with the order of declarations,
> especially if macros are involved.
>
> I can only assume nobody has tried calling a large C++ library
> from D (Qt doesn't count, no namespaces). Imagine manually
> organising namespaces in one huge bindings file instead of being
> able to copy the file layout of the C++ headers!
>
> Sigh.
>
> Atila
>

+1

You know how many times I've been upset about this, including the same day
that the C++ namespace feature was merged without consulting anyone in the
community that intended to use it.

Make a PR that implements namespace as a string... I will use that fork of
D forever.

>
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://lists.puremagic.com/pipermail/digitalmars-d/attachments/20180728/6fd18f0e/attachment.html>