Trait Display 

pub trait Display {
    // Required method
    fn fmt(&self, f: &mut Formatter<'_>) -> Result<(), Error>;
}

Format trait for an empty format, {}.

Implementing this trait for a type will automatically implement the ToString trait for the type, allowing the usage of the .to_string() method. Prefer implementing the Display trait for a type, rather than ToString.

Display is similar to Debug, but Display is for user-facing output, and so cannot be derived.

For more information on formatters, see the module-level documentation.

Completeness and parseability

Display for a type might not necessarily be a lossless or complete representation of the type. It may omit internal state, precision, or other information the type does not consider important for user-facing output, as determined by the type. As such, the output of Display might not be possible to parse, and even if it is, the result of parsing might not exactly match the original value.

However, if a type has a lossless Display implementation whose output is meant to be conveniently machine-parseable and not just meant for human consumption, then the type may wish to accept the same format in FromStr, and document that usage. Having both Display and FromStr implementations where the result of Display cannot be parsed with FromStr may surprise users.

Internationalization

Because a type can only have one Display implementation, it is often preferable to only implement Display when there is a single most “obvious” way that values can be formatted as text. This could mean formatting according to the “invariant” culture and “undefined” locale, or it could mean that the type display is designed for a specific culture/locale, such as developer logs.

If not all values have a justifiably canonical textual format or if you want to support alternative formats not covered by the standard set of possible formatting traits, the most flexible approach is display adapters: methods like str::escape_default or Path::display which create a wrapper implementing Display to output the specific display format.

Examples

Implementing Display on a type:

use std::fmt;

struct Point {
    x: i32,
    y: i32,
}

impl fmt::Display for Point {
    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
        write!(f, "({}, {})", self.x, self.y)
    }
}

let origin = Point { x: 0, y: 0 };

assert_eq!(format!("The origin is: {origin}"), "The origin is: (0, 0)");

Required Methods

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

Formats the value using the given formatter.

Errors

This function should return Err if, and only if, the provided Formatter returns Err. String formatting is considered an infallible operation; this function only returns a Result because writing to the underlying stream might fail and it must provide a way to propagate the fact that an error has occurred back up the stack.

Examples

use std::fmt;

struct Position {
    longitude: f32,
    latitude: f32,
}

impl fmt::Display for Position {
    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
        write!(f, "({}, {})", self.longitude, self.latitude)
    }
}

assert_eq!(
    "(1.987, 2.983)",
    format!("{}", Position { longitude: 1.987, latitude: 2.983, }),
);

Dyn Compatibility

This trait is dyn compatible.

In older versions of Rust, dyn compatibility was called "object safety".

Implementors

impl Display for !

impl Display for AccessError

impl Display for AddrParseError

impl Display for rquickjs::alloc::alloc::AllocError

impl Display for allocator_api2::stable::alloc::AllocError

impl Display for Arguments<'_>

impl Display for AsciiChar

impl Display for Backtrace

impl Display for BorrowError

impl Display for BorrowMutError

impl Display for ByteStr

impl Display for ByteString

impl Display for CharTryFromError

impl Display for DecodeUtf16Error

impl Display for std::ffi::os_str::Display<'_>

impl Display for std::path::Display<'_>

impl Display for relative_path::Display<'_>

impl Display for rquickjs::alloc::io::Error

impl Display for rquickjs::alloc::fmt::Error

impl Display for rquickjs::Error

impl Display for dlopen2::err::Error

impl Display for ErrorKind

impl Display for core::char::EscapeDebug

impl Display for core::ascii::EscapeDefault

impl Display for core::char::EscapeDefault

impl Display for core::char::EscapeUnicode

impl Display for Exception<'_>

impl Display for ExitStatus

impl Display for ExitStatusError

impl Display for FixedOffset

impl Display for FromBytesUntilNulError

impl Display for FromBytesWithNulError

impl Display for FromPathError

Available on crate feature std only.

impl Display for FromUtf8Error

impl Display for FromUtf16Error

impl Display for FromVecWithNulError

impl Display for rquickjs::alloc::slice::GetDisjointMutError

impl Display for indexmap::GetDisjointMutError

impl Display for GetTimezoneError

impl Display for IntoStringError

impl Display for IpAddr

impl Display for Ipv4Addr

impl Display for Ipv6Addr

Writes an Ipv6Addr, conforming to the canonical style described by RFC 5952.

impl Display for JoinPathsError

impl Display for LayoutError

impl Display for Location<'_>

impl Display for NaiveDate

The Display output of the naive date d is the same as d.format("%Y-%m-%d").

The string printed can be readily parsed via the parse method on str.

Example

use chrono::NaiveDate;

assert_eq!(format!("{}", NaiveDate::from_ymd_opt(2015, 9, 5).unwrap()), "2015-09-05");
assert_eq!(format!("{}", NaiveDate::from_ymd_opt(0, 1, 1).unwrap()), "0000-01-01");
assert_eq!(format!("{}", NaiveDate::from_ymd_opt(9999, 12, 31).unwrap()), "9999-12-31");

ISO 8601 requires an explicit sign for years before 1 BCE or after 9999 CE.

assert_eq!(format!("{}", NaiveDate::from_ymd_opt(-1, 1, 1).unwrap()), "-0001-01-01");
assert_eq!(format!("{}", NaiveDate::from_ymd_opt(10000, 12, 31).unwrap()), "+10000-12-31");

impl Display for NaiveDateTime

The Display output of the naive date and time dt is the same as dt.format("%Y-%m-%d %H:%M:%S%.f").

It should be noted that, for leap seconds not on the minute boundary, it may print a representation not distinguishable from non-leap seconds. This doesn’t matter in practice, since such leap seconds never happened. (By the time of the first leap second on 1972-06-30, every time zone offset around the world has standardized to the 5-minute alignment.)

Example

use chrono::NaiveDate;

let dt = NaiveDate::from_ymd_opt(2016, 11, 15).unwrap().and_hms_opt(7, 39, 24).unwrap();
assert_eq!(format!("{}", dt), "2016-11-15 07:39:24");

Leap seconds may also be used.

let dt =
    NaiveDate::from_ymd_opt(2015, 6, 30).unwrap().and_hms_milli_opt(23, 59, 59, 1_500).unwrap();
assert_eq!(format!("{}", dt), "2015-06-30 23:59:60.500");

impl Display for NaiveTime

The Display output of the naive time t is the same as t.format("%H:%M:%S%.f").

The string printed can be readily parsed via the parse method on str.

It should be noted that, for leap seconds not on the minute boundary, it may print a representation not distinguishable from non-leap seconds. This doesn’t matter in practice, since such leap seconds never happened. (By the time of the first leap second on 1972-06-30, every time zone offset around the world has standardized to the 5-minute alignment.)

Example

use chrono::NaiveTime;

assert_eq!(format!("{}", NaiveTime::from_hms_opt(23, 56, 4).unwrap()), "23:56:04");
assert_eq!(
    format!("{}", NaiveTime::from_hms_milli_opt(23, 56, 4, 12).unwrap()),
    "23:56:04.012"
);
assert_eq!(
    format!("{}", NaiveTime::from_hms_micro_opt(23, 56, 4, 1234).unwrap()),
    "23:56:04.001234"
);
assert_eq!(
    format!("{}", NaiveTime::from_hms_nano_opt(23, 56, 4, 123456).unwrap()),
    "23:56:04.000123456"
);

Leap seconds may also be used.

assert_eq!(
    format!("{}", NaiveTime::from_hms_milli_opt(6, 59, 59, 1_500).unwrap()),
    "06:59:60.500"
);

impl Display for NormalizeError

impl Display for NulError

impl Display for OutOfRange

impl Display for OutOfRangeError

impl Display for PanicHookInfo<'_>

impl Display for PanicInfo<'_>

impl Display for PanicMessage<'_>

impl Display for ParseBoolError

impl Display for ParseCharError

impl Display for ParseError

impl Display for core::num::float_parse::ParseFloatError

impl Display for num_traits::ParseFloatError

impl Display for ParseIntError

impl Display for ParseMonthError

impl Display for ParseWeekdayError

impl Display for RecvError

impl Display for std::sync::mpsc::RecvTimeoutError

impl Display for RelativePath

impl Display for RelativePathBuf

impl Display for RelativeToError

impl Display for RoundingError

impl Display for SocketAddr

impl Display for SocketAddrV4

impl Display for SocketAddrV6

impl Display for String

impl Display for StripPrefixError

impl Display for SystemTimeError

impl Display for TimeDelta

impl Display for ToCasefold

impl Display for ToLowercase

impl Display for ToTitlecase

impl Display for ToUppercase

impl Display for TryFromCharError

impl Display for TryFromFloatSecsError

impl Display for TryFromIntError

impl Display for TryFromSliceError

impl Display for std::fs::TryLockError

impl Display for std::sync::mpsc::TryRecvError

impl Display for rquickjs::alloc::collections::TryReserveError

impl Display for indexmap::TryReserveError

impl Display for hashbrown::TryReserveError

impl Display for allocator_api2::stable::raw_vec::TryReserveError

impl Display for Type

impl Display for UnorderedKeyError

impl Display for Utc

impl Display for Utf8Error

impl Display for VarError

impl Display for Weekday

impl Display for WeekdaySet

Print the collection as a slice-like list of weekdays.

Example

use chrono::Weekday::*;
assert_eq!("[]", WeekdaySet::EMPTY.to_string());
assert_eq!("[Mon]", WeekdaySet::single(Mon).to_string());
assert_eq!("[Mon, Fri, Sun]", WeekdaySet::from_array([Mon, Fri, Sun]).to_string());

impl Display for WouldBlock

impl Display for WriterPanicked

impl Display for bool

impl Display for char

impl Display for f16

impl Display for f32

impl Display for f64

impl Display for i8

impl Display for i16

impl Display for i32

impl Display for i64

impl Display for i128

impl Display for isize

impl Display for str

impl Display for u8

impl Display for u16

impl Display for u32

impl Display for u64

impl Display for u128

impl Display for usize

impl<'a, I, B> Display for DelayedFormat<I>

where I: Iterator<Item = B> + Clone, B: Borrow<Item<'a>>,

Available on crate feature alloc only.

impl<'a> Display for EscapeAscii<'a>

impl<'a> Display for rquickjs::alloc::str::EscapeDebug<'a>

impl<'a> Display for rquickjs::alloc::str::EscapeDefault<'a>

impl<'a> Display for rquickjs::alloc::str::EscapeUnicode<'a>

impl<'js> Display for CaughtError<'js>

impl<B> Display for Cow<'_, B>

where B: Display + ToOwned + ?Sized, <B as ToOwned>::Owned: Display,

impl<E> Display for Report<E>

where E: Error,

impl<F> Display for FromFn<F>

where F: Fn(&mut Formatter<'_>) -> Result<(), Error>,

impl<K, V, S, A> Display for OccupiedError<'_, K, V, S, A>

where K: Debug, V: Debug, A: Allocator,

impl<L, R> Display for Either<L, R>

where L: Display, R: Display,

impl<Ptr> Display for Pin<Ptr>

where Ptr: Display,

impl<T, A> Display for Arc<T, A>

where T: Display + ?Sized, A: Allocator,

impl<T, A> Display for rquickjs::alloc::boxed::Box<T, A>

where T: Display + ?Sized, A: Allocator,

impl<T, A> Display for allocator_api2::stable::boxed::Box<T, A>

where T: Display + ?Sized, A: Allocator,

impl<T, A> Display for Rc<T, A>

where T: Display + ?Sized, A: Allocator,

impl<T, A> Display for UniqueArc<T, A>

where T: Display + ?Sized, A: Allocator,

impl<T, A> Display for UniqueRc<T, A>

where T: Display + ?Sized, A: Allocator,

impl<T> Display for &T

where T: Display + ?Sized,

impl<T> Display for &mut T

where T: Display + ?Sized,

impl<T> Display for std::sync::nonpoison::mutex::MappedMutexGuard<'_, T>

where T: Display + ?Sized,

impl<T> Display for std::sync::poison::mutex::MappedMutexGuard<'_, T>

where T: Display + ?Sized,

impl<T> Display for std::sync::nonpoison::rwlock::MappedRwLockReadGuard<'_, T>

where T: Display + ?Sized,

impl<T> Display for std::sync::poison::rwlock::MappedRwLockReadGuard<'_, T>

where T: Display + ?Sized,

impl<T> Display for std::sync::nonpoison::rwlock::MappedRwLockWriteGuard<'_, T>

where T: Display + ?Sized,

impl<T> Display for std::sync::poison::rwlock::MappedRwLockWriteGuard<'_, T>

where T: Display + ?Sized,

impl<T> Display for std::sync::nonpoison::mutex::MutexGuard<'_, T>

where T: Display + ?Sized,

impl<T> Display for std::sync::poison::mutex::MutexGuard<'_, T>

where T: Display + ?Sized,

impl<T> Display for async_lock::mutex::MutexGuard<'_, T>

where T: Display + ?Sized,

impl<T> Display for MutexGuardArc<T>

where T: Display + ?Sized,

impl<T> Display for NonZero<T>

where T: ZeroablePrimitive + Display,

impl<T> Display for PoisonError<T>

impl<T> Display for std::sync::oneshot::RecvTimeoutError<T>

impl<T> Display for ReentrantLockGuard<'_, T>

where T: Display + ?Sized,

impl<T> Display for Ref<'_, T>

where T: Display + ?Sized,

impl<T> Display for RefMut<'_, T>

where T: Display + ?Sized,

impl<T> Display for std::sync::nonpoison::rwlock::RwLockReadGuard<'_, T>

where T: Display + ?Sized,

impl<T> Display for std::sync::poison::rwlock::RwLockReadGuard<'_, T>

where T: Display + ?Sized,

impl<T> Display for async_lock::rwlock::RwLockReadGuard<'_, T>

where T: Display + ?Sized,

impl<T> Display for RwLockReadGuardArc<T>

where T: Display,

impl<T> Display for RwLockUpgradableReadGuard<'_, T>

where T: Display + ?Sized,

impl<T> Display for RwLockUpgradableReadGuardArc<T>

where T: Display + ?Sized,

impl<T> Display for std::sync::nonpoison::rwlock::RwLockWriteGuard<'_, T>

where T: Display + ?Sized,

impl<T> Display for std::sync::poison::rwlock::RwLockWriteGuard<'_, T>

where T: Display + ?Sized,

impl<T> Display for async_lock::rwlock::RwLockWriteGuard<'_, T>

where T: Display + ?Sized,

impl<T> Display for RwLockWriteGuardArc<T>

where T: Display + ?Sized,

impl<T> Display for Saturating<T>

where T: Display,

impl<T> Display for SendError<T>

impl<T> Display for SendTimeoutError<T>

impl<T> Display for ThinBox<T>

where T: Display + ?Sized,

impl<T> Display for std::sync::poison::TryLockError<T>

impl<T> Display for std::sync::oneshot::TryRecvError<T>

impl<T> Display for TrySendError<T>

impl<T> Display for UserDataError<T>

impl<T> Display for Wrapping<T>

where T: Display,

impl<Tz> Display for Date<Tz>

where Tz: TimeZone, <Tz as TimeZone>::Offset: Display,

impl<Tz> Display for DateTime<Tz>

where Tz: TimeZone, <Tz as TimeZone>::Offset: Display,

impl<W> Display for IntoInnerError<W>