extern(C++, ...) only supports identifiers

[MoonlightSentinel]

The following declarations are rejected by libdparse:

enum abc = "abc";
__gshared:

extern(C++, "abc") int k;
extern(C++, "a", "b", "c") int m;
extern(C++, (abc)) int n;
extern(C++, ("abc")) int o;

(Allthough some of them aren't even documented in the spec)

[WebFreak001]

what isn't in the spec should also be reported to D

[MoonlightSentinel]

what isn't in the spec should also be reported to D

Gonna do that and maybe fix it along the way.

onlineapp.d(3): Error: undefined identifier abc

Made the example compilable.

[WebFreak001]

actually all of your reported code here is wrong according to the spec: https://dlang.org/spec/attribute.html#linkage

Only identifier lists are allowed, never strings

[MoonlightSentinel]

extern(C++, <string>) is definitly under-documented but has it's use-cases.

Gonna do that and maybe fix it along the way.

[WebFreak001]

does it differ from extern(C++, Foo.Bar)? How does one use it? Would it generate a different AST that needs to be interpreted differently?

[MoonlightSentinel]

I think it was intended as a more flexible alternative to an identifier, so extern(C++, "Foo.Bar") should be identical to extern(C++, Foo.Bar) (but there are some quirks IIRC). See e.g. the C++ bindings in Druntime for a practical example.

DMD code

EDIT: There is already this PR to document this feature but it got stalled

[Geod24]

Any serious user of C++ bindings is going to use extern(C++, string-or-CTFEable), not the extern(C++, identifier) feature. But yeah it is very under-documented, both in the spec and in cpp_interface page.

[WebFreak001]

can someone explain what it even does with strings? I didn't really look a lot but where I looked I couldn't find any information