Objective-C: Returning int to BOOL method

Question

I am new to Objective-C and i wonder why this method compiles, can anyone explain me why?

Thank you

-(BOOL) isEnabled{
   return 56;
}

There's an implicit cast - the last line is effectively: `return (BOOL)56;`. — Paul R, Jun 06 '12 at 12:52

score 6 · Accepted Answer · answered Jun 06 '12 at 12:56

6

A BOOL in Objective-C is a typedef of signed char. Since 56 fits in that type, the implicit conversion from a literal int results in no data loss.

answered Jun 06 '12 at 12:56

Jonathan Grynspan

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Zillan, also note that that this may break code if it relies on a `YES` or `NO` value. E.g. `if([self isEnabled] == YES]` would fail while `if([self isEnabled])` would work. – Joe Jun 06 '12 at 13:01
Yep, which is why normal coding style avoids comparing against those constants, and only uses them for assignment. – Jonathan Grynspan Jun 06 '12 at 13:04
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You should really check out this article: http://weblog.bignerdranch.com/564-bools-sharp-corners/ – Brian Palma Jun 06 '12 at 13:22

James Webster · Answer 2 · 2012-06-06T13:13:29.833

0

You can think of a BOOL in objective-c as

false === 0 === nil   //Anything that is zero or nil is false
true = !false         //Anything that is NOT zero or nil is true.

56 therefore returns true because it is not zero

edited Jun 06 '12 at 13:13

answered Jun 06 '12 at 12:53

James Webster

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No it isn't. A BOOL in Objective-C is a `signed char`. – Jonathan Grynspan Jun 06 '12 at 12:54
My "definition" was a bit misleading, I've amended. – James Webster Jun 06 '12 at 12:56
but `NSLog(@"%d",[self isenabled]);` returns `56`. Isn't that weird? – Zillan Jun 06 '12 at 12:57
No, it's expected. `56` fits in `signed char`. – Jonathan Grynspan Jun 06 '12 at 12:58
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Mathematically a boolean is true or false, but in objective c, your boolean can store a number of values. Zero values are treated as false. Non-zero values are true with the exception of multiples of 256 as I've added to my answer. – James Webster Jun 06 '12 at 12:58
Its not actually a boolean type, @JamesWebster. It's still an (in most C implementations) 8-bit ***signed*** integral value. You may be confusing `BOOL` with the 2-value C99 `_Bool` or C++ `bool` types, but they are not equivalent. – Jonathan Grynspan Jun 06 '12 at 13:02
@JonathanGrynspan What in my answer suggests I think it's a 2-value type? – James Webster Jun 06 '12 at 13:03
The entirety of your answer suggests that. – Jonathan Grynspan Jun 06 '12 at 13:04
'Be aware that since the unsigned char is limited 0-255' means that there are 256 values. – James Webster Jun 06 '12 at 13:05
Wrong, but not 2 values. I've removed the extraneous information as it's making the answer convoluted. – James Webster Jun 06 '12 at 13:13
The `BOOL` type is actually broken. In C, non zero integers are considered to be true but `(BOOL) (x * 256)` where x is an integer is false because the typecast discards all the non zero bits. – JeremyP Jun 06 '12 at 13:22

Objective-C: Returning int to BOOL method

2 Answers2