# icu_datetime [![crates.io](https://img.shields.io/crates/v/icu_datetime)](https://crates.io/crates/icu_datetime)

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Localized formatting of dates, times, and time zones.

This module is published as its own crate ([`icu_datetime`](https://docs.rs/icu_datetime/latest/icu_datetime/))
and as part of the [`icu`](https://docs.rs/icu/latest/icu/) crate. See the latter for more details on the ICU4X project.

ICU4X datetime formatting follows the Unicode UTS 35 standard for [Semantic Skeletons](https://unicode.org/reports/tr35/tr35-dates.html#Semantic_Skeletons).
First you choose a _field set_, then you configure the formatting _options_ to your desired context.

1. Field Sets: [`icu::datetime::fieldsets`](fieldsets)
2. Options: [`icu::datetime::options`](options)

ICU4X supports formatting in over one dozen _calendar systems_, including Gregorian, Buddhist,
Islamic, and more. The calendar system is usually derived from the locale, but it can also be
specified explicitly.

The main formatter in this crate is [`DateTimeFormatter`], which supports all field sets,
options, and calendar systems. Additional formatter types are available to developers in
resource-constrained environments.

The formatters accept input types from the [`calendar`](icu_calendar) and
[`timezone`](icu_timezone) crates:

1. [`Date`](icu_calendar::Date)
2. [`DateTime`](icu_calendar::DateTime)
3. [`Time`](icu_calendar::Time)
4. [`UtcOffset`](icu_timezone::UtcOffset)
5. [`TimeZoneInfo`](icu_timezone::TimeZoneInfo)
6. [`CustomZonedDateTime`](icu_timezone::CustomZonedDateTime)

Not all inputs are valid for all field sets.

## Binary Size Tradeoffs

The datetime crate has been engineered with a focus on giving developers the ability to
tune binary size to their needs. The table illustrates the two main tradeoffs, field sets
and calendar systems:

| Factor | Static (Lower Binary Size) | Dynamic (Greater Binary Size) |
|---|---|---|
| Field Sets | Specific [`fieldsets`] types | Enumerations from [`fieldsets::enums`] |
| Calendar Systems | [`FixedCalendarDateTimeFormatter`] | [`DateTimeFormatter`] |

If formatting times and time zones without dates, consider using [`TimeFormatter`].

## Examples

```rust
use icu::calendar::DateTime;
use icu::datetime::fieldsets;
use icu::datetime::DateTimeFormatter;
use icu::locale::{locale, Locale};
use writeable::assert_writeable_eq;

// Field set for year, month, day, hour, and minute with a medium length:
let field_set = fieldsets::YMDT::medium().hm();

// Create a formatter for Argentinian Spanish:
let locale = locale!("es-AR");
let dtf = DateTimeFormatter::try_new(locale.into(), field_set).unwrap();

// Format something:
let datetime = DateTime::try_new_iso(2025, 1, 15, 16, 9, 35).unwrap();
let formatted_date = dtf.format_any_calendar(&datetime);

assert_writeable_eq!(formatted_date, "15 de ene de 2025, 4:09 p. m.");
```

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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).