Objective-C Programming: The Big Nerd Ranch Guide

enum

Often you will need to define a set of constants. For example, imagine that you were developing a blender with five speeds: Stir, Chop, Liquefy, Pulse, and Ice Crush. Your class Blender would have a method called setSpeed:. It would be best if the type indicated that only one of the five speeds was allowed. To do this, you would define an enumeration:

enum BlenderSpeed {
    BlenderSpeedStir = 1,
    BlenderSpeedChop = 2,
    BlenderSpeedLiquify = 5,
    BlenderSpeedPulse = 9,
    BlenderSpeedIceCrush = 15
};

@interface Blender : NSObject
{
    // speed must be one of the five speeds
    enum BlenderSpeed speed;
}

// setSpeed: expects one of the five speeds
- (void)setSpeed:(enum BlenderSpeed)x;
@end

Developers get tired of typing enum BlenderSpeed, so ...