rustmax::std::fmt

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, }),
);

Trait DisplayCopy item path

§Completeness and parseability

§Internationalization

§Examples

Required Methods§

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

§Errors

§Examples

Implementors§

impl Display for HuffmanTreeError

impl Display for CheckedCastError

impl Display for PodCastError

impl Display for bzip2::mem::Error

impl Display for Tz

impl Display for codespan_reporting::files::Error

impl Display for DecodeKind

impl Display for Compression

impl Display for exr::error::Error

impl Display for gif::encoder::EncodingError

impl Display for EncodingFormatError

impl Display for gif::reader::decoder::DecodingError

impl Display for globset::ErrorKind

impl Display for AdditionError

impl Display for hdrhistogram::errors::CreationError

impl Display for RecordError

impl Display for SubtractionError

impl Display for httparse::Error

impl Display for humantime::date::Error

impl Display for humantime::duration::Error

impl Display for GetTimezoneError

impl Display for InvalidStringList

impl Display for icu_collections::codepointtrie::error::Error

impl Display for icu_locale_core::parser::errors::ParseError

impl Display for PreferencesParseError

impl Display for DataErrorKind

impl Display for image_webp::decoder::DecodingError

impl Display for image_webp::encoder::EncodingError

impl Display for indexmap::GetDisjointMutError

impl Display for IpNet

impl Display for jpeg_decoder::error::Error

impl Display for libloading::error::Error

impl Display for InsertError

impl Display for matchit::error::MatchError

impl Display for nix::errno::consts::Errno

impl Display for nix::errno::consts::Errno

impl Display for PollTimeoutTryFromError

impl Display for nix::sys::signal::Signal

impl Display for nix::sys::signal::Signal

impl Display for BlendOp

impl Display for DisposeOp

impl Display for png::decoder::stream::DecodingError

impl Display for png::encoder::EncodingError

impl Display for ppmd_rust::Error

impl Display for qoi::error::Error

impl Display for rand::distributions::bernoulli::BernoulliError

impl Display for WeightedError

impl Display for ColorPrimaries

impl Display for MatrixCoefficients

impl Display for PixelRange

impl Display for TransferCharacteristics

impl Display for InvalidConfig

impl Display for rav1e::api::config::rate::Error

impl Display for PredictionModesSetting

impl Display for SGRComplexityLevel

impl Display for SceneDetectionSpeed

impl Display for SegmentationLevel

impl Display for EncoderStatus

impl Display for FrameType

impl Display for CpuFeatureLevel

impl Display for Tune

impl Display for BlockSize

impl Display for ravif::error::Error

impl Display for StartError

impl Display for Ast

impl Display for regex_syntax::ast::ErrorKind

impl Display for regex_syntax::error::Error

impl Display for regex_syntax::hir::ErrorKind

impl Display for EarlyDataError

impl Display for EncodeError

impl Display for EncryptError

Trait Display