Can I create static c callable library?

[Jonathan M Davis]

On Tuesday, September 25, 2018 5:03:11 AM MDT John Burton via Digitalmars-d-
learn wrote:
> I need to write a library to statically link into a c program.
> Can I write this library in D?
> Will I be able to use proper D abilities like gc? Obviously the
> public interface will need to be basic c callable functions...
>
> I 'main' is a c program will this work?

If you use -betterC, then it's trivial, because your D program is restricted
to extern(C) functions and features which don't require druntime. It can
also be done without -betterC (and thus with druntime), but it gets to be
_way_ more of a pain, because it requires that you manually initialize
druntime - either by forcing whatever is using your "C" library to call a
specific function to initialize druntime before using any of its normal
functions or by having every function in the library check whether druntime
has been initialized yet and initialize it if it hasn't been before it does
whatever it's supposed to do. And of course, if you pass any GC-allocated
memory out of the library, you have to worry about calling all of the
appropriate GC functions so that it knows not to free it and knowing when to
tell the GC that that memory can be freed. It's all very feasible and all
very annoying. In general, it's far, far easier to write D programs that
call into C code than to write C programs that call into D code. That's part
of why some folks are so excited about -betterC. It makes it _way_ easier to
write D libraries that can be called from C or C++ - though because you lose
out on so many D features in the process (like the GC), whether it's even
worth it is highly debatable.

- Jonathan M Davis