OK, I'm going to state the obvious here in the hope it will be
considered afresh. :)
On Sunday, 3 January 2016 at 17:53:38 UTC, Walter Bright wrote:
5. I don't share the opinion that a C++ namespace introducing a
scope, just as it does in C++, is something weird and
unexpected.
Wait a second: D has modules with clever import rules and no
global scope to manage name collisions instead of namespaces. See
the bullet here under "features to drop from C++":
http://dlang.org/overview.html#features_to_drop
What's now going on is the reintroduction of this dropped feature
in a way that is at cross purposes to the underlying D language
philosophy.
In the end the disputed difficult comes down to this:
extern(C++, ns1) int fn(int x);
and
extern(C++, ns2) int fn(int x);
have different mangled names but the same D-source name. They
also have the same C++ source name.
In the C++ source this collision is averted by namespaces. In the
D source where the namespace mechanism has been designed out in
favor of the module mechanism, this collision should be averted
using the module mechanism.
If you still believe you want to be able to place the colliding
externals in the same module, i.e. not use D's collision
avoidance mechanism, what's needed is simply the ability to have
two different D source names for the two functions specified in
the two declarations. This is just a name change, not an entire
new scope with all the complexity that would entail in the
namespace situation.
Perhaps there's a way to do this in D already: how do you link to
a C function whose name is 'new' or some other D keyword?
In any case, drawing a distinction between the D source name and
the C++ source name (or the external source name in general) in
the external declaration would do the job. e.g.
extern(C++, ns1, fn) int fn1(int x);
extern(C++, ns2, fn) int fn2(int x);
In each case the external declaration has enough information to
compute the mangled name and attach it to a D source name without
collision.
My opinion: Injecting C++ bad design into D in the name of
linkage is wrong, ugly, and over complicated. I don't think the
alternative mechanism suggested in the preceding paragraph or
anything similar is necessary either, since D modules are the
replacement for namespaces in going from C++ to D, and they can
do the job. But something like that alternative is a lot less
awful.
