On Oct 11, 2008, at 3:26 PM, Seth Willits wrote:
Note that nowhere in there is there anything related to how many arguments there are, or what type they are.Ahh. I guess I mis-remembered varargs. I thought they did have a count. I'mYou can tell how often I've had to use it ;-)
Nope --you remembered correctly. Almost.How varargs are interpreted is entirely up to whatever is interpreting the varargs. Here are two methods from the kit:
NSString.h:+ (id)stringWithFormat:(NSString *)format, ...;NSArray.h:+ (id)arrayWithObjects:(id)firstObj, ... NS_REQUIRES_NIL_TERMINATION;
And one method that I'm making up: Foo.h:+ (id)fooWithCount: (unsigned) i bars: (Bar *) bar1, ...;All three are perfectly valid varargs style methods and all three have completely different means of interpreting the varargs. The key to varargs is that that there has to be something somewhere -- be it documentation or format string -- that tells the vararg taking method how to decade the unknown set of arguments properly.
And in all cases, there has to be some magic somewhere that indicates when to stop trying to pull more args off the stack. Hence the fragility of varargs. And, thank goodness for that NS_REQUIRES_NIL_TERMINATION macro (which expands to a compiler attribute). Prior to that, programs would compile without warning and then crash at runtime because someone would do:
[NSArray arrayWithObjects: one, two, three];No warning. Often work in debug mode sometimes. *boom* most of the time.
Varargs really aren't much fun. Powerful, but a pain. b.bum
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