extern(C++, ns)

[Manu via Digitalmars-d]

On 3 January 2016 at 15:45, Walter Bright via Digitalmars-d <
digitalmars-d at puremagic.com> wrote:

> On 1/2/2016 9:19 PM, Manu via Digitalmars-d wrote:
>
>> In addition to that rant, extern(C++) seems to fail at forward
>> referencing. Any
>> time I have 2 modules that refer to eachother, suddenly the order of
>> everything
>> is critical. I can sometimes resolve these problems by moving imports out
>> of the
>> global scope, but often it's terminal, and I need to restructure
>> everything in
>> awkward and unnatural ways to break the stalemate.
>>
>> I know I'll just get complaints from people to submit bugs; I have submit
>> lots,
>> and in many cases, I've tried to, but they're almost impossible to
>> produce in
>> isolation, only when a project gets 'real', ie, big enough that it's
>> realistic
>> in scope does it all start to break down. It's really hard to reduce a
>> bug that
>> I don't understand, somewhere among a program with 30-ish interconnected
>> modules. It's worse when the structure of the project is unnatural, a
>> requirement forced by the namespace issue, and everything is already
>> really
>> brittle as a result.
>>
>> The thing is, it almost all comes back to the pseudo-namespaces
>> (sprinkled with
>> weird forward referencing issues). Maybe it sounded good at the time, but
>> it
>> doesn't work in practice. If that was fixed, then we'd stand on solid
>> ground,
>> and it might be possible to reduce bugs and move forward in that
>> environment.
>>
>
> They're not pseudo-namespaces. C++ namespaces in D are scoped namespaces
> and follow all the D scoping and name lookup rules. They are mangled,
> however, like C++ namespace scoped symbols are mangled.
>

I don't want that. That's what modules are for.
extern(C++) should only state where the external C++ function is to be
found. If the user wants the D symbol under a namespace to match C++, let
them do so explicitly. But they probably already are via the module scope.

Given a C++ symbol 'NS::CSymbol', the D symbol 'x.y.NS.CSymbol' bears no
meaningful relation. D still prefixes the module scope.

The user will almost certainly instead do:

module NS; // a module for the C++ thing
extern(C++, NS) void func();

Which would give them the symbol 'NS.NS.func'. Surely what they intended
was 'NS.func' to match the C++ symbol?


I am not aware of any forward reference issues with C++ namespaces, so
> without an example, I cannot do anything.
>

https://issues.dlang.org/show_bug.cgi?id=15389

Over a month ago, nearer to the start of my descent into madness. I suspect
this had lead to some mis-diagnoses of issues.
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