I'm writing a game using the Chipmunk physics engine, and I'd like to store a pointer to an Objective-C object in every body's userData
field. I know I need to use a bridging cast to cast between id
and void *
, but I'm not sure the way I'm doing it is safe:
// When body is created
cpBody *body = cpBodyNew(...);
UserData *userData = [[UserData alloc] init];
cpBodySetUserData(body, CFBridgingRetain(body));
...
// When body is destroyed
UserData *userData = cpBodyGetUserData(body);
CFBridgingRelease(userData);
cpBodyFree(body);
This code seems to work, but I've also read that you're only supposed to use CFBridging*()
on objects that can be toll-free bridged to Core Foundation types. Since UserData
is derived from NSObject
, and NSObject
isn't on the list of toll-free bridged types, I seem to be breaking that rule.
Is my code okay because I eventually call CFBridgingRelease
and don't try to pass the object to any other Core Foundation functions, or is there another way I should be going about transferring Objective-C objects in and out of C?
It's safe.
NSObject
is toll-free bridged to a genericCFTypeRef
. Also, I'm assuming you aren't calling any other Core Foundation functions on thevoid*
, so it hardly matters.