structure Constant list in Objective-C

In Objective-C, a constant list is a collection of fixed values that do not change throughout the flow of the program. These lists can be defined using the NS_ENUM macro or the NS_OPTIONS macro depending on the intended usage.

Here is an example of how to use constant list using the NS_ENUM macro:

typedef NS_ENUM(NSInteger, Month) {
    January,
    February,
    March,
    April,
    May,
    June,
    July,
    August,
    September,
    October,
    November,
    December
};

In this example, we've defined a constant list of all 12 months of the year. The NS_ENUM macro generates an enumeration of type NSInteger with the specified identifier Month. This enumeration is a list of constants that represent each month.

Here is an example of how to use constant list using the NS_OPTIONS macro:

typedef NS_OPTIONS(NSUInteger, Colors) {
    Red = 1 << 0,
    Green = 1 << 1,
    Blue  = 1 << 2,
    Yellow = Red | Green,
    Magenta = Red | Blue,
    Cyan = Green | Blue,
    White = Red | Green | Blue
};

In this example, we've defined a constant list of different colors. The NS_OPTIONS macro generates an enumeration of type NSUInteger with the specified identifier Colors. This enumeration is a list of bit-masks that represent different combinations of colors.

In both examples, we've defined a set of fixed values that can be used throughout our program. Using these constant lists can make code more readable, easier to maintain, and more predictable. When you need to use one of the values, you simply reference it by name, like this: Month.January or Colors.Red.