6-Iteration.md

Iterating Over Values

Iterating over calendrical values is a common problem, especially when it comes to building a UI around calendars. Many developers want to iterate over every day in a month, or every month in a year. Time makes this easy:

let thisMonth = Clocks.system.thisMonth()
let daysInThisMonth = thisMonth.days()

for day in daysInThisMonth {
    // day is an Absolute<Day>
}

By default, all absolute TimePeriods provide convenience methods for iterating over subcomponents:

• An Absolute<Year> provides months() and days() to iterate over the months in the year and the days in the year
• An Absolute<Month> provides days() and hours() to iterate over the days or hours in the month
• etc

However, you can also create your own value sequence, by using the AbsoluteTimePeriodSequence provided by Time:

let day1: Absolute<Day> = ...
let day2: Absolute<Day> = ...

let dayRange = day1 ..< day2

let everyOtherDay = AbsoluteTimePeriodSequence(range: dayRange, stride: .days(2))
for day in everyOtherDay {
    // ...
}

The AbsoluteTimePeriodSequence type provides several convenience constructors for performing different kinds of iterations.