Date is the opaque type for all Date values. Values of this type are guaranteed to represent valid proleptic Gregorian calendar dates.

date constructs a Date value given a year, a month and a day. Invalid values are clamped to the nearest valid date.

year returns a Date's year as an Int.

month returns a Date's month as an Int. Guaranteed to be in the range [1, 12].

day returns a Date's year as an Int. Guaranteed to be valid for the Date's (year, month) pair and in the range [1, 31].

Data type used to represent the days of the week.

weekday returns the day of week for a given Date.

This uses Sakamoto's method to determine the day of week.

setYear updates a Date's year. Invalid values are clamped to the nearest valid date.

setMonth updates a Date's month. Invalid values are clamped to the nearest valid date.

setDay updates a Date's day. Invalid values are clamped to the nearest valid date.

addYears adds a relative number (positive or negative) of years to a Date, ensuring that the return value represents a valid Date. If the new date is not valid, days are subtracted from it until a valid Date can be produced.

addMonths adds a relative number (positive or negative) of months to a Date, ensuring that the return value represents a valid Date. Its semantics are the same as addYears.

days adds an exact number (positive or negative) of days to a Date. Adding or subtracting days always produces a valid Date so there is no fuzzing logic here like there is in add{Months,Years}.

compare two Dates.

DateDelta represents a delta between two dates.

delta returns the relative number of years, months and days between two Dates.

toISO8601 converts a Date into its string representation.

fromISO8601 parses an ISO8601-formatted date string into a Date.

toTuple converts a Date value into a (year, month, day) tuple. This is useful if you want to use Dates as Dict keys.

fromTuple converts a (year, month, day) tuple into a Date value.

isValidDate returns True if the given year, month and day represent a valid date.

isLeapYear returns True if the given year is a leap year. The rules for leap years are as follows:

• A year that is a multiple of 400 is a leap year.
• A year that is a multiple of 100 but not of 400 is not a leap year.
• A year that is a multiple of 4 but not of 100 is a leap year.

daysInMonth returns the number of days in a month given a specific year, taking leap years into account.

• A regular year has 365 days and the corresponding February has 28 days.
• A leap year has 366 days and the corresponding February has 29 days.