How to compile Phobos with other D code to create a shared library?

[data pulverizer]

On Friday, 4 June 2021 at 15:19:17 UTC, bachmeier wrote:
>
> It requires an R package if you want to call D functions from 
> R. You need to link to R itself if you want to do something 
> like pass a vector from R to D and then access that data from 
> D. Since R is aware of the location of all the underlying 
> libraries, it's easiest to let it generate the dub.sdl for you.
>
> I guess you're using the older .C interface [as done 
> here](http://users.stat.umn.edu/~geyer/rc/). Good enough if 
> passing double* and int* pointers to D functions will suffice. 
> Only thing you need to do to initialize the D runtime is add 
> this to your D code
>
> ```
> struct DllInfo;
>
> extern(C) void R_init_libfoo(DllInfo * info) {
>     Runtime.initialize();
> }
> ```
>
> where foo is the name of the library you're loading (foo.so).

I've just read the documentation and had a go, **compiling with 
GDC worked for both `.C` and `.Call`**.

I tried with all three compilers DMD, LDC, and GDC, and looked at 
the outputs with the nm tool. I don't think this matters much but 
DMD and LDC are more likely to list functions (DMD) or symbols in 
referenced modules (LDC) as weak symbols. I think the more likely 
the reason GDC worked is because it is a GNU compiler this has 
full GLIBC compatibility with reference to the `librt.so.1` 
`GLIBC_PRIVATE` error.

The R ext documentation you kindly referenced says:

*"By default, R uses the operating-system-specific dynamic loader 
to lookup the symbol in all loaded DLLs and the R executable or 
libraries it is linked to."*

and that:

*"Registering routines has two main advantages: it provides a 
faster way to find the address of the entry point via tables 
stored in the DLL at compilation time, and it provides a run-time 
check that the entry point is called with the right number of 
arguments and, optionally, the right argument types."*

So registering symbols is not the issue. The error was specific 
to GLIBC which is probably why the GNU compiler worked.

Thank you.