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.

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

impl Display for Infallible

impl Display for IpAddr

impl Display for SocketAddr

impl Display for bool

impl Display for char

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

impl Display for AllocError

impl Display for LayoutError

impl Display for UnorderedKeyError

impl Display for TryReserveError

impl Display for FromVecWithNulError

impl Display for IntoStringError

impl Display for NulError

impl Display for ParseBoolError

impl Display for Utf8Error

impl Display for FromUtf8Error

impl Display for FromUtf16Error

impl Display for String

impl Display for TryFromSliceError

impl Display for core::ascii::EscapeDefault

impl Display for BorrowError

impl Display for BorrowMutError

impl Display for CharTryFromError

impl Display for ParseCharError

impl Display for DecodeUtf16Error

impl Display for core::char::EscapeDebug

impl Display for core::char::EscapeDefault

impl Display for core::char::EscapeUnicode

impl Display for ToLowercase

impl Display for ToUppercase

impl Display for TryFromCharError

impl Display for FromBytesUntilNulError

impl Display for FromBytesWithNulError

impl Display for Ipv4Addr

impl Display for Ipv6Addr

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

impl Display for AddrParseError

impl Display for SocketAddrV4

impl Display for SocketAddrV6

impl Display for ParseFloatError

impl Display for ParseIntError

impl Display for TryFromIntError

impl Display for Location<'_>

impl Display for PanicInfo<'_>

impl Display for PanicMessage<'_>

impl Display for TryFromFloatSecsError

impl Display for Arguments<'_>

impl Display for Error

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

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

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

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

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

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

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

impl<F> Display for FromFn<F>

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

impl<Ptr> Display for Pin<Ptr>

where Ptr: Display,

impl<T> Display for &T

where T: Display + ?Sized,

impl<T> Display for &mut 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 NonZero<T>

where T: ZeroablePrimitive + Display,

impl<T> Display for Saturating<T>

where T: Display,

impl<T> Display for Wrapping<T>

where T: Display,

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

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

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

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

impl<const N: usize> Display for GetManyMutError<N>