Question

For example, this method from NSCalendar takes a bitmask:

- (NSDate *)dateByAddingComponents:(NSDateComponents *)comps toDate:(NSDate *)date options:(NSUInteger)opts

So options can be like:

NSUInteger options = kCFCalendarUnitYear;

or like:

NSUInteger options = kCFCalendarUnitYear | kCFCalendarUnitMonth | kCFCalendarUnitDay;

What I don’t get is, how is this actually done? I mean: How can they pull out those values which are merged into options? If I wanted to program something like this, that can take a bitmask, how would that look?

Answer 1

To do this, you want to bitwise AND the value you’re testing against the mask, then see if the result of the ANDing equals the mask itself:

if ((options & kCFCalendarUnitYear) == kCFCalendarUnitYear) {
   // do whatever
}