Objective-C: Result of casting id to BOOL?

Question

Does the following function return YES if object != nil?

- (BOOL)boolForObject:(id)object {
    return (BOOL)object;
}

I've tested with object = [[NSObject alloc] init] but got mixed results.

Answer 1

A pointer is larger than a BOOL, so when you cast it will truncate and take only the 8 least significant bits of the pointer and make it a BOOL. If those bits all happen to be zero then that is equivalent to NO.

So to answer your question, no it does not (well sometimes it will depending on the pointer value)

Here's an example with using Xcode 5.1.1 on 32 bit architecture:

void* p = (void*)0xfeeeff00;
BOOL  b = (BOOL)p;

NSLog(@"p=%08x (%lu), b=%08x (%lu)", (uint32_t)p, sizeof p, (uint32_t)b, sizeof b);

It prints out:

p=feeeff00 (4), b=00000000 (1)