Re: Difficulty integrating with Swift/Objective-C

[Taylan Kammer <taylan.kammer@gmail.com>]

On 06.09.2021 12:21, paul wrote:
> Hello again list, Taylan,
> 
> On 2021-09-05 at 18:26 AEST, quoth Taylan Kammer <taylan.kammer@gmail.com>:
>> To narrow down the issue, I'd attempt a few things, in order:
>>
>> 1. Compile only the C code, adding a main() function, just to make sure the OS
>>    and the chosen Guile version and such are working fine with    each other.
>>
>> 2. Compile pure Objective-C code, calling that run_guile() function firstly
>>    directly from the main() function in main.m of the    Objective-C program, and
>>    commenting out the NSApplicationMain() call that would    initialize Apple's
>>    application framework.
>>
>> 3. See if reactivating the NSApplicationMain() call causes problems.  (It should
>>    be called *after* the Guile initialization.)
>>
>> 4. See if you can use Guile's C functions from -applicationDidFinishLaunching:
>>    e.g. by doing: scm_c_eval_string("(begin (display    'HelloWorld) (newline))")
>>
>> If that works, we now have an Objective-C + Guile application, and want to move
>> to using Swift instead.  This is where my Apple knowledge hits its limits because
>> I never used Swift. :-)
>>
>> But I guess Swift should have something equivalent to the main() function of C and
>> Objective-C, and calling Guile initialization from there might do the trick.
> 
> Thank you very much for your tips.  I was actually able to unstick myself with your suggestions: first i created a blank Objective-C CLI app and integrated Guile, that worked well!  Next i created a new, blank, Objective-C AppKit GUI app.  The same procedure worked well there, too.
> 
> The more challenging bit was learning how to take my existing Swift app and (re-)introduce a main() in Objective-C.  Because it turns out that Swift has some conveniences that cause it to autogenerate a _main symbol behind-the-scenes.  In any case you can turn that off and create an Objective-C main function (my project didn't have Objective-C to start with, but it was enough to create a new file with a main() copied from my earlier from-scratch experiments) which - long story short - i was able to modify and get Guile booting correctly!  I was even able to complete step 4, to my surprise (sort of), and call scm_c_eval_string straight from my Application Kit code.  This takes a bit of fiddling (Apple's so-called Precompiled Bridging Header) to make Swift aware of C-land functions, bu
 t my app actually already has a Rust-based core which i call out to with this mechanism so here i was on firmer ground.
> 
> I think there must have been something weird about the state of my project last night, because initially i was still having the EXC_BAD_ACCESS issues, but making a new branch off my main and doing the above worked well.
> 
> It should be said that i still couldn't use the Homebrew-packaged version of Guile because of the JIT errors i described elsewhere, but this isn't a blocker because i'm able to compile my own libguile with `--enable-jit=no`.
> 
> Thanks again, i spent all weekend messing with this and couldn't figure it out, your input was super useful.
> 
> All the best,
> p.

I'm happy to hear it worked, and thanks for reporting back. :-)

Personally I don't do any Apple-related development these days but it's
good to know what does and doesn't work.

-- 
Taylan