Struct DateTimeFormatter

pub struct DateTimeFormatter<FSet: DateTimeNamesMarker> { /* private fields */ }

DateTimeFormatter is a formatter capable of formatting dates and/or times from a calendar selected at runtime.

For more details, please read the crate root docs.

📏 This item has a stack size of 384 bytes on the stable toolchain at release date.

Implementations

impl<FSet> DateTimeFormatter<FSet>

where FSet::D: DateDataMarkers, FSet::T: TimeMarkers, FSet::Z: ZoneMarkers, FSet: GetField<CompositeFieldSet> + DateTimeMarkers,

pub fn try_new( prefs: DateTimeFormatterPreferences, field_set: FSet, ) -> Result<Self, DateTimeFormatterLoadError>

where Baked: AllAnyCalendarFormattingDataMarkers<FSet>,

Creates a new DateTimeFormatter from compiled data with datetime components specified at build time.

This method will pick the calendar off of the locale; and if unspecified or unknown will fall back to the default calendar for the locale. See AnyCalendarKind for a list of supported calendars.

Use this constructor for optimal data size and memory use if you know the required datetime components at build time. If you do not know the datetime components until runtime, use a with_components constructor.

✨ Enabled with the compiled_data Cargo feature.

📚 Help choosing a constructor

Examples

Basic usage:

use icu::datetime::fieldsets::YMD;
use icu::datetime::input::Date;
use icu::datetime::DateTimeFormatter;
use icu::locale::locale;
use writeable::assert_writeable_eq;

let formatter = DateTimeFormatter::try_new(
    locale!("en-u-ca-hebrew").into(),
    YMD::medium(),
)
.unwrap();

let date = Date::try_new_iso(2024, 5, 8).unwrap();

assert_writeable_eq!(formatter.format(&date), "30 Nisan 5784");

pub fn try_new_with_buffer_provider<P>( provider: &P, prefs: DateTimeFormatterPreferences, field_set: FSet, ) -> Result<Self, DateTimeFormatterLoadError>

where P: BufferProvider + ?Sized,

A version of [Self :: try_new] that uses custom data provided by a BufferProvider.

✨ Enabled with the serde feature.

📚 Help choosing a constructor

pub fn try_new_unstable<P>( provider: &P, prefs: DateTimeFormatterPreferences, field_set: FSet, ) -> Result<Self, DateTimeFormatterLoadError>

where P: ?Sized + AllAnyCalendarFormattingDataMarkers<FSet> + AllAnyCalendarExternalDataMarkers,

A version of Self::try_new that uses custom data provided by a DataProvider.

📚 Help choosing a constructor

⚠️ The bounds on provider may change over time, including in SemVer minor releases.

impl<FSet: DateTimeMarkers> DateTimeFormatter<FSet>

where FSet::D: DateInputMarkers, FSet::T: TimeMarkers, FSet::Z: ZoneMarkers,

pub fn format_same_calendar<I>( &self, datetime: &I, ) -> Result<FormattedDateTime<'_>, MismatchedCalendarError>

where I: ?Sized + InSameCalendar + AllInputMarkers<FSet>,

Formats a datetime, checking that the calendar system is correct.

If the datetime is not in the same calendar system as the formatter, an error is returned.

Examples

Mismatched calendars will return an error:

use icu::datetime::fieldsets::YMD;
use icu::datetime::input::Date;
use icu::datetime::DateTimeFormatter;
use icu::datetime::MismatchedCalendarError;
use icu::locale::locale;

let formatter = DateTimeFormatter::try_new(
    locale!("en-u-ca-hebrew").into(),
    YMD::long(),
)
.unwrap();

let date = Date::try_new_gregorian(2023, 12, 20).unwrap();

assert!(matches!(
    formatter.format_same_calendar(&date),
    Err(MismatchedCalendarError { .. })
));

A time cannot be passed into the formatter when a date is expected:

use icu::datetime::input::Time;
use icu::datetime::DateTimeFormatter;
use icu::datetime::fieldsets::YMD;
use icu::locale::locale;

let formatter = DateTimeFormatter::try_new(
    locale!("es-MX").into(),
    YMD::long(),
)
.unwrap();

// error[E0277]: the trait bound `Time: AllInputMarkers<fieldsets::YMD>` is not satisfied
formatter.format_same_calendar(&Time::midnight());

pub fn format<'a, I>(&'a self, datetime: &I) -> FormattedDateTime<'a>

where I: ?Sized + ConvertCalendar, I::Converted<'a>: Sized + AllInputMarkers<FSet>,

Formats a datetime after first converting it to the formatter’s calendar.

Examples

Mismatched calendars convert and format automatically:

use icu::datetime::fieldsets::YMD;
use icu::datetime::input::Date;
use icu::datetime::DateTimeFormatter;
use icu::datetime::MismatchedCalendarError;
use icu::locale::locale;
use writeable::assert_writeable_eq;

let formatter = DateTimeFormatter::try_new(
    locale!("en-u-ca-hebrew").into(),
    YMD::long(),
)
.unwrap();

let date = Date::try_new_roc(113, 5, 8).unwrap();

assert_writeable_eq!(formatter.format(&date), "30 Nisan 5784");

A time cannot be passed into the formatter when a date is expected:

use icu::datetime::input::Time;
use icu::datetime::DateTimeFormatter;
use icu::datetime::fieldsets::YMD;
use icu::locale::locale;

let formatter = DateTimeFormatter::try_new(
    locale!("es-MX").into(),
    YMD::long(),
)
.unwrap();

// error[E0277]: the trait bound `Time: AllInputMarkers<fieldsets::YMD>` is not satisfied
formatter.format(&Time::midnight());

impl<FSet: DateTimeMarkers> DateTimeFormatter<FSet>

pub fn try_into_typed_formatter<C>( self, ) -> Result<FixedCalendarDateTimeFormatter<C, FSet>, MismatchedCalendarError>

where C: CldrCalendar + IntoAnyCalendar,

Attempt to convert this DateTimeFormatter into one with a specific calendar.

Returns an error if the type parameter does not match the inner calendar.

Examples

use icu::calendar::cal::Hebrew;
use icu::datetime::fieldsets::YMD;
use icu::datetime::input::Date;
use icu::datetime::DateTimeFormatter;
use icu::locale::locale;
use writeable::assert_writeable_eq;

let formatter = DateTimeFormatter::try_new(
    locale!("en-u-ca-hebrew").into(),
    YMD::long(),
)
.unwrap()
.try_into_typed_formatter::<Hebrew>()
.unwrap();

let date = Date::try_new_hebrew(5785, 1, 12).unwrap();

assert_writeable_eq!(formatter.format(&date), "12 Tishri 5785");

An error occurs if the calendars don’t match:

use icu::calendar::cal::Hebrew;
use icu::datetime::fieldsets::YMD;
use icu::datetime::input::Date;
use icu::datetime::DateTimeFormatter;
use icu::datetime::MismatchedCalendarError;
use icu::locale::locale;

let result = DateTimeFormatter::try_new(
    locale!("en-u-ca-buddhist").into(),
    YMD::long(),
)
.unwrap()
.try_into_typed_formatter::<Hebrew>();

assert!(matches!(result, Err(MismatchedCalendarError { .. })));

pub fn cast_into_fset<FSet2: DateTimeNamesFrom<FSet>>( self, ) -> DateTimeFormatter<FSet2>

Maps a DateTimeFormatter of a specific FSet to a more general FSet.

For example, this can transform a formatter for YMD to one for DateFieldSet.

Examples

use icu::calendar::Gregorian;
use icu::datetime::fieldsets::{enums::DateFieldSet, YMD};
use icu::datetime::input::Date;
use icu::datetime::DateTimeFormatter;
use icu::locale::locale;
use writeable::assert_writeable_eq;

let specific_formatter =
    DateTimeFormatter::try_new(locale!("fr").into(), YMD::medium())
        .unwrap();

// Test that the specific formatter works:
let date = Date::try_new_gregorian(2024, 12, 20).unwrap();
assert_writeable_eq!(specific_formatter.format(&date), "20 déc. 2024");

// Make a more general formatter:
let general_formatter = specific_formatter.cast_into_fset::<DateFieldSet>();

// Test that it still works:
assert_writeable_eq!(general_formatter.format(&date), "20 déc. 2024");

pub fn calendar(&self) -> Ref<'_, AnyCalendar>

Returns the calendar used in this formatter.

Examples

use icu::calendar::AnyCalendarKind;
use icu::datetime::fieldsets::YMD;
use icu::datetime::input::Date;
use icu::datetime::DateTimeFormatter;
use icu::locale::locale;
use writeable::assert_writeable_eq;

let formatter =
    DateTimeFormatter::try_new(locale!("th").into(), YMD::long()).unwrap();

assert_writeable_eq!(
    formatter.format(&Date::try_new_iso(2024, 12, 16).unwrap()),
    "16 ธันวาคม 2567"
);

assert_eq!(formatter.calendar().kind(), AnyCalendarKind::Buddhist);
assert_eq!(formatter.calendar().kind().as_bcp47_string(), "buddhist");

Trait Implementations

impl<FSet: Debug + DateTimeNamesMarker> Debug for DateTimeFormatter<FSet>

fn fmt(&self, f: &mut Formatter<'_>) -> Result

Formats the value using the given formatter.