Trait Display

1.0.0 · Source

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

Expand description

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§

1.0.0 · Source

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".

Display

Trait Display Copy item path

§Completeness and parseability

§Internationalization

§Examples

Required Methods§

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

§Errors

§Examples

Dyn Compatibility§

Implementors§

impl Display for otter_nodejs_tests::base64::DecodeError

impl Display for Kind

impl Display for LoadError

impl Display for State

impl Display for RoundingError

impl Display for otter_nodejs_tests::chrono::Weekday

impl Display for otter_nodejs_tests::chrono_tz::Tz

impl Display for AccountsSaveError

impl Display for ApiPieceOpError

impl Display for otter_nodejs_tests::ErrorKind

impl Display for Fatal

impl Display for Inapplicable

impl Display for Infallible

impl Display for InternalError

impl Display for InvalidScopedName

impl Display for otter_nodejs_tests::IpAddr

impl Display for LibraryLoadMFIncompat

impl Display for LibraryLoadError

impl Display for LinkKind

impl Display for VersionError

impl Display for MgmtError

impl Display for PacketFrameReadError

impl Display for PacketFrameWriteError

impl Display for PieceOpErrorPartiallyProcessed

impl Display for SVGProcessingError

impl Display for SVGSizeError

impl Display for SVGWidthOrHeight

impl Display for SocketAddr

impl Display for SpecError

impl Display for Void

impl Display for ZipError

impl Display for VarError

impl Display for FlexiLoggerError

impl Display for otter_nodejs_tests::flexi_logger::Level

impl Display for otter_nodejs_tests::flexi_logger::LevelFilter

impl Display for otter_nodejs_tests::fs::TryLockError

impl Display for otter_nodejs_tests::humantime::DurationError

impl Display for otter_nodejs_tests::humantime::TimestampError

impl Display for AsciiChar

impl Display for FromBytesWithNulError

impl Display for otter_nodejs_tests::inventory::core::slice::GetDisjointMutError

impl Display for otter_nodejs_tests::mpsc::RecvTimeoutError

impl Display for otter_nodejs_tests::mpsc::TryRecvError

impl Display for otter_nodejs_tests::nix::errno::Errno

impl Display for Signal

impl Display for InetAddr

impl Display for otter_nodejs_tests::nix::sys::socket::IpAddr

impl Display for SockAddr

impl Display for otter_nodejs_tests::otter_support::imports::Error

impl Display for PwdError

impl Display for BernoulliError

impl Display for WeightedError

impl Display for otter_nodejs_tests::regex::Error

impl Display for otter_nodejs_tests::rmp_serde::decode::Error

impl Display for otter_nodejs_tests::rmp_serde::encode::Error

impl Display for SubstErrorKind

impl Display for KeyError

impl Display for LogicOperator

impl Display for MathOperator

impl Display for otter_nodejs_tests::tera::Value

impl Display for otter_nodejs_tests::toml::Value

impl Display for otter_nodejs_tests::toml::ser::Error

impl Display for Offset

impl Display for otter_nodejs_tests::toml_de::Error

impl Display for LogicError

impl Display for RangeImpossible

impl Display for CompressionMethod

impl Display for ParseAlphabetError

impl Display for base64::decode::DecodeError

Trait Display