DIP61: redone to do extern(C++,N) syntax

[Byron via Digitalmars-d]

On Mon, 28 Apr 2014 10:27:19 -0400, Steven Schveighoffer wrote:

> On Sun, 27 Apr 2014 15:54:51 -0400, Walter Bright
> <newshound2 at digitalmars.com> wrote:
> 
>> http://wiki.dlang.org/DIP61
> 
> I think there is a big problem with name lookup here.
> 
> Consider this code:
> 
> module foo;
> 
> void func() {}
> 
> module bar;
> 
> extern(C) func();
> 
> module prog;
> 
> import foo;
> import bar;
> 
> void main()
> {
>     func(); // error foo.func(); // ok bar.func(); // ok, uses C binding
>     (no name mangling)
> }
> 
> In this case, even though the C function is not mangled or in any other
> namespace, the module can be used for unambiguous calling.
> 
> But in your proposal, the name qualifiers could be either C++ namespaces
> or D modules. This presents an unnecessary ambiguity.
> 
> e.g.
> 
> module foo;
> 
> void func() {}
> 
> module bar;
> 
> extern(C++, foo) void func(); // foo::func in C++ land
> 
> module prog;
> 
> import foo;
> import bar;
> 
> void main()
> {
>     func(); // error foo.func(); // ALSO error bar.func(); // Not error,
>     BUT it's actually calling foo::func from C++
> land!
> }
> 
> I think we cannot change name lookup rules for C++ symbols, because the
> D module system already owns those.
> 
> An alternative is that you could create an alternate way to
> disambiguate.
> Let's pick a strawman called _cpp, just to illustrate:
> 
> void main()
> {
>     func(); // error still foo.func(); // calls D's foo module's func
>     bar.func(); // calls D's bar module's func (defined as foo::func)
>     _cpp.func(); // error, _cpp denotes we are using namespace
>     qualifiers,
> and there is no global C++ func
>     _cpp.foo.func(); // calls D's bar module's func.
>     bar._cpp.foo.func(); // ditto
> }
> 
> Really, _cpp could be anything. But I think hijacking D's module
> qualifiers does not help. To make things seamless, you could make it ::,
> but I know many people have objections to that.
> 
> -Steve

why not  import _cpp = bar;   ?