mikeash.com pyblog/friday-qa-2011-10-28-generic-block-proxying.html comments

Leo Natan - 2019-09-25 11:10:42

Wed, 25 Sep 2019 11:10:42 GMT

For future reference, Core Foundation includes a function which achieves something similar:

extern id __NSMakeSpecialForwardingCaptureBlock(const char *signature, void (^handler)(NSInvocation *inv));

Signature of a block can be obtained using

extern const char* _Block_signature(id block);

or from a protocol using

extern const char* _protocol_getMethodTypeEncoding(Protocol* protocol, SEL name, BOOL isRequiredMethod, BOOL isInstanceMethod);

The resulting block object can be passed as a normal block, and once invoked, the provided callback will be called with the invocation object.

R.George - 2013-03-22 02:01:27

Fri, 22 Mar 2013 02:01:27 GMT

Reading long after the fact here... I was playing around with something related (trying to synthesize property accessors at runtime), and noticed that the digging up of the forwarding IMP: [self methodForSelector: @selector(thisDoesNotExistOrAtLeastItReallyShouldnt)] can be shortened to _objc_msgForward. I could hardly believe it, but it's actually public, and declared in objc/message.h along with _objc_msgForward_stret.

As far as I can tell, the only current portable way to tell whether any given method uses stret vs. normal calling conventions is to search -[NSMethodSignature debugDescription] for the magic string. No lie. Enhancement request has been filed.