How do you read parameters in a callback function?

Start with the didDiscoverPeripheral callback and its class.addMethod registration, then read the referenced src/msg_send.zig implementation around line 283. Document how the Objective-C selector maps to callback parameters and how the discovered values can be accessed. Done means a clear example answers the parameter and object-extraction questions.

I've been poking around the code and struggling to work out how to read the parameters in a callback function handler. Given I cant find an example, I am not sure where to start. I am at the point where I am able to get the objc bluetooth api to report back discovery of bluetooth devices. But how do I extract the information?

(My long term goal is to eventually have a zig cross platform bluetooth api, just working on it on the side when I have time.)

//- (void)centralManager:(CBCentralManager *)central
// didDiscoverPeripheral:(CBPeripheral *)peripheral
//     advertisementData:(NSDictionary<NSString *,id> *)advertisementData
//                  RSSI:(NSNumber *)RSSI {
fn didDiscoverPeripheral(
    _: objc.c.id, // What are these for?
    _: objc.c.SEL, // What are these for?
    centralId: objc.c.id, // Do you add parameters like this?
    peripheralId: objc.c.id, // Do you add parameters like this?
) callconv(.c) void {
    //    NSLog(@"Discovered device: %@ (RSSI: %@)", peripheral.name ?: @"Unknown", RSSI);
    info("found device ", .{});

    info("   id: {any} {any} ", .{ centralId, peripheralId });

    // Just guessing
    const central = objc.Object.fromId(centralId);
    const peripheral = objc.Object.fromId(peripheralId);
    info("   obj: {any} {any} ", .{ central, peripheral });

    // Just guessing
    const name = peripheral.msgSend(objc.Object, "name", .{});
    info("   name: {any} ", .{name});
}

For reference, here is how I am setting up this callback handler to be called:

        // Register a CBResponder to handle bluetooth callback/events.
        const class = objc.allocateClassPair(objc.getClass("NSObject"), "CBResponder") orelse return error.ObjCFailure;

        // https://github.com/mitchellh/zig-objc/blob/c8de82ff80281215ad92900866dab7103a8efa8b/src/msg_send.zig#L283
        _ = class.addMethod("centralManagerDidUpdateState:", updateState);
        _ = class.addMethod("centralManager:didDiscoverPeripheral:advertisementData:RSSI:", didDiscoverPeripheral);
        const protocol = objc.getProtocol("CBCentralManagerDelegate") orelse return error.ObjCFailure;
        _ = objc.c.class_addProtocol(class.value, protocol.value);
        objc.registerClassPair(class);
        const class_obj = class.msgSend(objc.Object, "alloc", .{});

        //_centralManager = [[CBCentralManager alloc] initWithDelegate:self queue:nil];
        const bluetoothManager = objc.getClass("CBCentralManager") orelse return error.ObjCFailure;
        const bluetoothManagerAlloc = bluetoothManager.msgSend(objc.Object, "alloc", .{});
        bt_global = bluetoothManagerAlloc.msgSend(objc.Object, "init", .{});
        bt_global.?.setProperty("delegate", class_obj);