Handy constants

Another element that is easily overlooked, but can make code and life so much easier: Convenience Constants. Take some examples:

CGPointZero

CGRectZero

CGSizeZero

CGRectInfinite - mostly used in Core Image contexts

CGRectNull - not equal to CGRectZero, returned by e.g. CGRectIntersection()

NSNotFound

CGAffineTransformIdentity

UIEdgeInsetsZero

UITrackingRunLoopMode

NSFoundationVersionNumber

NSRunLoopCommonModes

NSEventTrackingRunLoopMode