D as an extension language

[Don Clugston]

Bill Baxter wrote:
> This is just a random musing, but curious if anyone had any comments.
> 
> I work mostly in C++ but recently I've been doing more with farming out 
> tricky bits to Python so I can develop those parts more rapidly.  That 
> works pretty well, but for some things Python is just not fast enough. 
> But still, while prototyping at least, I'd rather use a language that's 
> easier to develop in than C++.
> 
> That's where the question comes in... How about D as an extension 
> language?  For the time being, using C++ is a fact of life for a lot of 
> people due to extensive dependence on piles of C++ legacy code.  But if 
> I'm writing a new module or new functionality, it doesn't matter how it 
> does it's thing under the hood as long as it presents a C++ interface to 
> the rest of the system.
> 
> So how hard is it to do this sort of thing?
> What tools are out there to help?
> What tools would really be ideal to have but are missing?
> 
> It seems like it should be easier than the Python<->C++ connection 
> because D understands C ABI.  But most of what I've seen is about how D 
> can call C code, not how C++ can call D code.

I'm doing a lot of Windows stuff in C++, calling DLLs written in D. It's 
not hard. You just need to use extern(C) wrappers on the D functions, 
catch all the D exceptions before returning to C++, and make sure C++ 
doesn't hang onto any D pointers that could be gc-ed.
Otherwise, it's exactly the same as calling a C DLL.

I have some C++ code to simplify dynamic loading of D DLLs in Windows, 
if you're interested (it does the name mangling for you). Useless for 
Linux, of course.

> I think it's worth thinking about.  It is one more way that D could make 
> some inroads in a C++ entrenched world.

Absolutely.