Anyone using ObjCBlocks?

JonB

Has anyone been using ObjCBlocks that take multiple arguments in any APIs? I stumbled across what might be a pythonista bug, but it could easily just as well be my own stupidity.

I have started tackling AudioUnits to experiment with real time audio processing. To that end, I am using
AVAudioEngine
and installing a data tap, which takes a Block of this form

https://developer.apple.com/reference/avfoundation/avaudionodetapblock?language=objc

typedef void (^AVAudioNodeTapBlock)(
     AVAudioPCMBuffer *buffer, AVAudioTime *when);

The Python function I tried to use was

 def tap(_self, _sel, buffer, when)

however, the proper method seemed to be

 def tap(_self, when, buffer, _sel)

In other words, the argument order was backwards, except for the block itself. does the runtime swap arguments on us? Or is pythonista objc_utils doing something funny?

dgelessus

Maybe this has something to do with iOS's 64-bit vararg calling conventions being different from normal 64-bit ARM. I think we were discussing that issue on Slack once, when @lukaskollmer tried to get NSLog working on a 64-bit device.

The only reason I can think of why the argument order is so strange is that maybe _self is "early" enough in the list that it's passed as a register, and the rest of the arguments go on the stack, but somehow are in the wrong order?