Is Objective-C BOOL a Boolean Type?
While
BOOLmight look trivial, its definition is rather complex. It depends on which Apple platform and architecture you are targeting, which can result in unexpected behavior.[…]
Recently, I stumbled into a case where for the same code, macOS Intel and macOS Apple Silicon invoked different overloads.
[…]
As we can see, the
BOOLtype is either an alias toboolor an alias tosigned chardepending on the value of theOBJC_BOOL_IS_BOOLpreprocessor define.[…]
More than a decade later, as part of the C99 specification, the C language released support for boolean values through the
<stdbool.h>header. Then, later versions of the Objective-C runtime started conditionally aliasingBOOLto the newbooltype in modern Apple products. It is likely that older platform and architecture combinations still usesigned charfor legacy reasons.
Update (2024-01-10): Greg Parker:
BOOL’s type and sign-edness affect Objective-C type encodings, which are used by NSArchives and Distributed Objects and others, which affects binary and data file compatibility. BOOL’s type also affects C and C++ function calls and data structures. It’s not easy to change.
See also: Hacker News.
I was never a fan of BOOL. The C "boolean" type (before happened) was `int` and 0 meant NO, and != 0 meant YES. Good enough. I have no idea, why anyone thought changing this was a **good** idea.
Apple defined BOOL as `char` and YES as 1. This produced serious problems. As soon as you define YES to be 1, you now have brittle code, that fails on x == YES, if x is for example 2. Fine in C, broken in ObjC. The idea with `char` was to conserve some space, for programmers, that were too lazy to use a bitfield, but cared about wasted space enough to not want to use an `int`. Using char though made dealing with method return values (think: IMP) that much more complicated :rolleyes:
Apple should have typedef-ed BOOL to int and only defined NO. Maybe they could have added a macro `#define is( x) (x != 0)` as a replacement for YES, so you can write: `if( is( [foo whatever])`, but why would you even want to...
Now its too late and you cant get rid of BOOL. The new C `bool` type is a weird un-C like type, thats basically just a char with a restrictive value set. I am not fan of it either.