W3cubDocs

/Rust

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, }),
);

Implementors

impl Display for AsciiChar

1.34.0Source

impl Display for Infallible

impl Display for VarError

1.17.0Source

impl Display for FromBytesWithNulError

1.89.0Source

impl Display for std::fs::TryLockError

1.60.0Source

impl Display for ErrorKind

impl Display for IpAddr

impl Display for SocketAddr

1.86.0Source

impl Display for GetDisjointMutError

1.15.0Source

impl Display for RecvTimeoutError

impl Display for TryRecvError

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 !

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

1.26.0Source

impl Display for PanicInfo<'_>

1.81.0Source

impl Display for PanicMessage<'_>

impl Display for AllocError

1.28.0Source

impl Display for LayoutError

1.35.0Source

impl Display for TryFromSliceError

1.39.0Source

impl Display for std::ascii::EscapeDefault

1.65.0Source

impl Display for Backtrace

impl Display for ByteStr

impl Display for ByteString

1.13.0Source

impl Display for BorrowError

1.13.0Source

impl Display for BorrowMutError

1.34.0Source

impl Display for CharTryFromError

impl Display for DecodeUtf16Error

1.20.0Source

impl Display for std::char::EscapeDebug

1.16.0Source

impl Display for std::char::EscapeDefault

1.16.0Source

impl Display for std::char::EscapeUnicode

1.20.0Source

impl Display for ParseCharError

1.16.0Source

impl Display for ToLowercase

1.16.0Source

impl Display for ToUppercase

1.59.0Source

impl Display for TryFromCharError

impl Display for UnorderedKeyError

1.57.0Source

impl Display for TryReserveError

impl Display for JoinPathsError

1.87.0Source

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

1.69.0Source

impl Display for FromBytesUntilNulError

1.58.0Source

impl Display for FromVecWithNulError

impl Display for IntoStringError

impl Display for NulError

impl Display for std::io::Error

1.56.0Source

impl Display for WriterPanicked

impl Display for AddrParseError

impl Display for Ipv4Addr

impl Display for Ipv6AddrWrites an Ipv6Addr, conforming to the canonical style described by
RFC 5952.

impl Display for SocketAddrV4

impl Display for SocketAddrV6

impl Display for ParseFloatError

impl Display for ParseIntError

1.34.0Source

impl Display for TryFromIntError

1.63.0Source

impl Display for InvalidHandleErrorAvailable on Windows only.

1.63.0Source

impl Display for NullHandleErrorAvailable on Windows only.

1.26.0Source

impl Display for Location<'_>

1.26.0Source

impl Display for PanicHookInfo<'_>

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

impl Display for NormalizeError

impl Display for StripPrefixError

impl Display for ExitStatus

impl Display for ExitStatusError

impl Display for ParseBoolError

impl Display for Utf8Error

impl Display for FromUtf8Error

impl Display for FromUtf16Error

impl Display for String

impl Display for RecvError

impl Display for WouldBlock

1.26.0Source

impl Display for AccessError

impl Display for SystemTimeError

1.66.0Source

impl Display for TryFromFloatSecsError

impl Display for Arguments<'_>

impl Display for std::fmt::Error

1.60.0Source

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

1.34.0Source

impl<'a> Display for std::str::EscapeDebug<'a>

1.34.0Source

impl<'a> Display for std::str::EscapeDefault<'a>

1.34.0Source

impl<'a> Display for std::str::EscapeUnicode<'a>

impl<'a, K, V, A> Display for std::collections::btree_map::OccupiedError<'a, K, V, A>where
    K: Debug + Ord,
    V: Debug,
    A: Allocator + Clone,

impl<'a, K: Debug, V: Debug> Display for std::collections::hash_map::OccupiedError<'a, K, V>

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,

1.93.0Source

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

1.33.0Source

impl<Ptr> Display for Pin<Ptr>where
    Ptr: Display,

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

impl<T> Display for SendTimeoutError<T>

impl<T> Display for TrySendError<T>

impl<T> Display for &Twhere
    T: Display + ?Sized,

impl<T> Display for &mut Twhere
    T: Display + ?Sized,

impl<T> Display for ThinBox<T>where
    T: Display + ?Sized,

1.20.0Source

impl<T> Display for Ref<'_, T>where
    T: Display + ?Sized,

1.20.0Source

impl<T> Display for RefMut<'_, T>where
    T: Display + ?Sized,

1.28.0Source

impl<T> Display for NonZero<T>where
    T: ZeroablePrimitive + Display,

1.74.0Source

impl<T> Display for Saturating<T>where
    T: Display,

1.10.0Source

impl<T> Display for Wrapping<T>where
    T: Display,

impl<T> Display for SendError<T>

impl<T> Display for PoisonError<T>

impl<T, A> Display for 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 UniqueRc<T, A>where
    T: Display + ?Sized,
    A: Allocator,

impl<T, A> Display for Arc<T, A>where
    T: Display + ?Sized,
    A: Allocator,

impl<T, A> Display for UniqueArc<T, A>where
    T: Display + ?Sized,
    A: Allocator,

impl<T: Display + ?Sized> Display for ReentrantLockGuard<'_, T>

impl<T: ?Sized + Display> Display for std::sync::nonpoison::MappedMutexGuard<'_, T>

impl<T: ?Sized + Display> Display for std::sync::nonpoison::MappedRwLockReadGuard<'_, T>

impl<T: ?Sized + Display> Display for std::sync::nonpoison::MappedRwLockWriteGuard<'_, T>

impl<T: ?Sized + Display> Display for std::sync::nonpoison::MutexGuard<'_, T>

impl<T: ?Sized + Display> Display for std::sync::nonpoison::RwLockReadGuard<'_, T>

impl<T: ?Sized + Display> Display for std::sync::nonpoison::RwLockWriteGuard<'_, T>

impl<T: ?Sized + Display> Display for std::sync::MappedMutexGuard<'_, T>

impl<T: ?Sized + Display> Display for std::sync::MappedRwLockReadGuard<'_, T>

impl<T: ?Sized + Display> Display for std::sync::MappedRwLockWriteGuard<'_, T>

1.20.0Source

impl<T: ?Sized + Display> Display for std::sync::MutexGuard<'_, T>

1.20.0Source

impl<T: ?Sized + Display> Display for std::sync::RwLockReadGuard<'_, T>

1.20.0Source

impl<T: ?Sized + Display> Display for std::sync::RwLockWriteGuard<'_, T>

impl<W> Display for IntoInnerError<W>

© 2010 The Rust Project Developers
Licensed under the Apache License, Version 2.0 or the MIT license, at your option.
https://doc.rust-lang.org/std/fmt/trait.Display.html