@true and @​false have incorrect Obj-C type encoding (integer, not bool)

[llvmbot]

Bugzilla Link	13640
Resolution	MOVED
Resolved on	Aug 19, 2012 10:06
Version	3.1
OS	MacOS X
Attachments	test case
Reporter	LLVM Bugzilla Contributor
CC	@lattner

Extended Description

The Objective-C literals @​true and @​false result at runtime in NSNumber objects with incorrect type-encodings. The objects claim to be integers, not BOOLs (encoding "i", not "c".)

This has serious side effects: in particular, NSJSONSerialization doesn't realize these objects are supposed to be booleans, so it encodes them in JSON as "0" and "1", not "false" and "true". That's how I discovered this problem -- after "modernizing" my code to use @​true and @​false, the CouchDB server it communicates with started failing with HTTP 500 errors, because a parameter was being sent as an integer instead of a boolean.

Note that @​true isn't even compatible with kCFBooleanTrue or [NSNumber numberWithBool: YES], both of which generate type encoding "c".

Attached is a short test case that demonstrates the problem.

[llvmbot]

It was pointed out that the official syntax is @​YES and @​NO -- those are hardwired to turn into kCFBooleanTrue and kCFBooleanFalse, and do result in the right JSON encodings.

It's still odd that @​true, aka @(true), turns into an NSNumber with type-encoding "i" instead of "b", though, since @​encode(bool) is "b".

[lattner]

Hi Jens,

Please report Objective-C language issues through Apple's bug-reporter. Thanks!

-Chris