Unable to declare a C function pointer with varargs

[bcardiff]

Syntax error in ...: unexpected ',' in type (use parenthesis to disambiguate)

@[Link("objc")]
lib LibObjC
  type SEL = Void*
  type IMP = Pointer(UInt8), LibObjC::SEL, ... -> Pointer(UInt8)
end

[asterite]

For now you can use Void* forIMP.

I can see in class_addMethod you must pass an IMP. Can you get an IMP back from an objective-c call? And how do you use it?

We can add that feature to the language but I need to know how you would use it in order to implement it well.

[bcardiff]

I don't care, at least for now, getting a IMP from obj-c. I just need to create them on crystal and pass it to class_addMethod.

Each IMP instance will vary on the arguments after the 3rd param.

$AppDel_didFinishLaunching = -> (obj : UInt8*, _cmd : LibObjC::SEL, aNotification : UInt8*) {
}

If I declare IMP as Void* I get:

LibObjC.class_addMethod($x_MyAppDelegate_objc_class.obj, "applicationDidFinishLaunching:".to_sel.to_objc, $AppDel_didFinishLaunching, "v@:@")
# argument #3 of 'LibObjC#class_addMethod' must be LibObjC::IMP, not (Pointer(UInt8), LibObjC::SEL, Pointer(UInt8) -> Int32)

if I try to cast, I get:

LibObjC.class_addMethod($x_MyAppDelegate_objc_class.obj, "applicationDidFinishLaunching:".to_sel.to_objc, $AppDel_didFinishLaunching as LibObjC::IMP, "v@:@")
# can't cast (Pointer(UInt8), LibObjC::SEL, Pointer(UInt8) -> Void) to LibObjC::IMP

My only workaround is to define many IMP and menu addMethod aliases, one for each signature :-(

At least I would need a generic function pointer.

FYI: this crocoa code is WIP and not pushed yet.

[asterite]

You can try doing alias IMP = Void* and then do the cast. Does that work?

[bcardiff]

Same result using alias IMP = Void*

with $AppDel_didFinishLaunching

argument #3 of 'LibObjC#class_addMethod' must be Pointer(Void), not (Pointer(UInt8), LibObjC::SEL, Pointer(UInt8) -> Void)

with $AppDel_didFinishLaunching as LibObjC::IMP

can't cast (Pointer(UInt8), LibObjC::SEL, Pointer(UInt8) -> Void) to Pointer(Void)

[bcardiff]

I push the spike around this on https://github.com/manastech/crocoa/tree/master/samples/bundled_application . Just in case is easier to check further ideas.

$ build.sh
$ open Sample.app

[asterite]

I forgot our procs are always a pair containing a pointer to the function and a pointer to the closure context (which is null if it's not a closure). You can access that pointer by invoking pointer:

alias IMP = Void*
f = ->{ 1 }
f.pointer as IMP # works

You can use that workaround until we implement variadic function pointers (only for C bindings, I guess).

Note that Function#pointer doesn't check that the proc is not a closure: if it is and you pass that pointer to C things will probably won't work, so this is unsafe (or we should raise if someone tries to get the pointer of a closure).

[bcardiff]

Yeap, it did the trick. You choose whether to leave this issue open or not. For me is enough with the workaround.

I agree that an exception for closures should be raised.