NSGetSizeAndAlignment(): unsupported type encoding spec

[niklassaers]

Hi guys,

In my mixed Swift/ObjC project, I copy/pasted the instructions under "Example usage" into a ObjC file. At

NSSet *retainCycles = [detector findRetainCycles];

I got an objc_exception

NSGetSizeAndAlignment(): unsupported type encoding spec 'b' at 'b2' in 'b2'

from FBClassStrongLayout.m line 43.

I use FBRetainCycleDetector (0.1.1) via CococaPods (with frameworks enabled)

[Gricha]

Hey! Interesting, in general some types are unavailable to query for (for example if you have a struct and this struct has bitfields at the beginning and some objects at the end, we wouldn't cover that).
Because NSGetSizeAndAlignment() can throw we have wrapped that in @try-catch block.

So that's the idea - the question is - why the exception was not caught. Frameworks might be to blame, I'll look into it a little bit more.

[Gricha]

Are you in debug mode? There is a good chance you are not crashing but are stopping in exception breakpoint. Could you try disabling this and check if the issue is still happening for you?

[kastiglione]

Yes, the 'b' is _C_BFLD, a bitfield.

Since there's some encoding parsing going on, I wonder if there should be a black list of known bad types, like bitfields, to avoid going down a path that is sure to fail.

[Gricha]

That is a good point. Especially that, IIRC, throwing and catching exception is not exactly "free" :P

Maintaining short check-list before falling in might be a good thing for performance, the question is if it's cheaper to sometimes throw & catch, or constantly do a lookup in every ivar check.

Thoughts?

[JackLSH2016]

只是路过！

[HaloWang]

In my UIViewController class, I create a property like this:
@property (nonatomic, strong) void(^aBlock)();
and I'm sure there is a retaincycle between my viewController and this property.
When I use FBRetainCycleDetector, my problem stop at FBClassStrongLayout.m line 43, with a global All Exceptions Breakpoint.

[Gricha]

Yes, NSGetSizeAndAlignment throws exception that will be caught by exception breakpoint. The safest is to turn off exception breakpoint when using retain cycle detector.