extern(C) and name mangling

[Mike Parker]

On Wednesday, 16 December 2020 at 04:45:34 UTC, Dave P. wrote:

>
> Oh interesting, so I only need extern(C) for declaring symbols 
> I’m linking to and
> for symbols I want to export to C. I had sort of assumed that D 
> might have
> different calling conventions for different things, but that 
> makes things a lot easier.
>

Not so fast! :-)

extern(C) does affect the calling convention on Windows x86. 
There's also extern(Windows), which changes a function to the 
stdcall calling convention used by the Win32 API (and OpenGL 
implementations on Windows, and a handful of other libraries). 
And there's no guarantee that as D moves to new platforms that 
there won't be other exceptions joining x86 Windows.

That's why I said I'm not sure I'd ever pass a templated function 
pointer to C. It isn't going to work on 32-bit Windows, or with 
any stdcall C function, right now, and possibly other platforms 
in the future.

So as a default, you should always be explicit with your 
extern(x) linkage attributes on functions even when you aren't 
actually linking with C, and only break that rule when it's 
necessary.