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# icu_calendar [](https://crates.io/crates/icu_calendar)
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Types for dealing with dates and custom calendars.
This module is published as its own crate ([`icu_calendar`](https://docs.rs/icu_calendar/latest/icu_calendar/))
and as part of the [`icu`](https://docs.rs/icu/latest/icu/) crate. See the latter for more details on the ICU4X project.
The [`types`] module has a lot of common types for dealing with dates.
[`Calendar`] is a trait that allows one to define custom calendars, and [`Date`]
can represent dates for arbitrary calendars.
The [`Iso`] and [`Gregorian`] types are implementations for the ISO and
Gregorian calendars respectively. Further calendars can be found in the [`cal`] module.
Most interaction with this crate will be done via the [`Date`] type.
Some of the algorithms implemented here are based on
Dershowitz, Nachum, and Edward M. Reingold. _Calendrical calculations_. Cambridge University Press, 2008.
## Examples
Examples of date manipulation using `Date` object. `Date` objects are useful
for working with dates, encompassing information about the day, month, year,
as well as the calendar type.
```rust
use icu::calendar::{types::Weekday, Date};
// Creating ISO date: 1992-09-02.
let mut date_iso = Date::try_new_iso(1992, 9, 2)
.expect("Failed to initialize ISO Date instance.");
assert_eq!(date_iso.day_of_week(), Weekday::Wednesday);
assert_eq!(date_iso.era_year().year, 1992);
assert_eq!(date_iso.month().ordinal, 9);
assert_eq!(date_iso.day_of_month().0, 2);
// Answering questions about days in month and year.
assert_eq!(date_iso.days_in_year(), 366);
assert_eq!(date_iso.days_in_month(), 30);
```
Example of converting an ISO date across Indian and Buddhist calendars.
```rust
use icu::calendar::cal::{Buddhist, Indian};
use icu::calendar::Date;
// Creating ISO date: 1992-09-02.
let mut date_iso = Date::try_new_iso(1992, 9, 2)
.expect("Failed to initialize ISO Date instance.");
assert_eq!(date_iso.era_year().year, 1992);
assert_eq!(date_iso.month().ordinal, 9);
assert_eq!(date_iso.day_of_month().0, 2);
// Conversion into Indian calendar: 1914-08-02.
let date_indian = date_iso.to_calendar(Indian);
assert_eq!(date_indian.era_year().year, 1914);
assert_eq!(date_indian.month().ordinal, 6);
assert_eq!(date_indian.day_of_month().0, 11);
// Conversion into Buddhist calendar: 2535-09-02.
let date_buddhist = date_iso.to_calendar(Buddhist);
assert_eq!(date_buddhist.era_year().year, 2535);
assert_eq!(date_buddhist.month().ordinal, 9);
assert_eq!(date_buddhist.day_of_month().0, 2);
```
[`ICU4X`]: ../icu/index.html
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## More Information
For more information on development, authorship, contributing etc. please visit [`ICU4X home page`](https://github.com/unicode-org/icu4x).