However Objective-C BOOL, as pointed out before, is just a typedef
for a char, and YES & NO are just typedefs, so there is no
coercion, so:
BOOL foo = 42;
if( foo == YES )
Would not take the branch.
Of course there is no need to ever write "if( foo == YES )", so
it's an easy
problem to avoid--just learn that a variable of type bool/BOOL is an
expression of type bool/BOOL and thus does not need to be compared
to a
bool/BOOL value in order to yield a bool/BOOL result.
But a similar "gotcha" case is:
BOOL isShift = [theEvent modifierFlags] & NSShiftKeyMask;
if (isShift) {
// this will never be hit, regardless of the state of the shift key!
}
This is because the result of the expression tests a single bit that
happens to be higher than will fit in the BOOL, resulting in isShift
always being 0.
OTOH, either:
if ([theEvent modifierFlags] & NSShiftKeyMask) {
// this works
}
BOOL isShift = ([theEvent modifierFlags] & NSShiftKeyMask) !=
NSShiftKeyMask; // explicitly test to see if that bit is set
if (isShift) {
// works as well
}
