Question

In the past, when I’ve had to compile something on Snow Leopard (or any older Mac OS X) and use some @selector that’s available on Lion and higher, I’ve done something like this:

if([foo respondsToSelector:@selector(awesomeLionSelector)]) {
    [foo awesomeLionSelector]
}

And this has worked great. So, now I’m trying to do the same thing for a new method that returns a float, but the following line:

float f = [foo awesomeLionSelectorWhichReturnsFloat];

throws a compile error: “cannot convert ‘objc_object*’ to ‘float’ in assignment”. This is because the compiler doesn’t know about the method and has to assume a return type of ‘id’.

What is the proper way to fix this?

Answer 1

EDIT: according to John Caswell comment, the correct runtime function to use is objc_msgSend_fpret(), which returns a double.

I think you should try your way with: objc_msgSend_stret():

objc_msgSend_stret

Sends a message with a data-structure return value to an instance of a class.

  void objc_msgSend_stret(void * stretAddr, id theReceiver, SEL theSelector,  ...)

Something like:

objc_msgSend_stret(&myFloatReturnValue, foo, @selector(awesomeLionSelector));