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, }),
);

Display

Trait Display Copy item path

§Completeness and parseability

§Internationalization

§Examples

Required Methods§

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

§Errors

§Examples

Implementors§

impl Display for BuildModel

impl Display for ShadowError

impl Display for AsciiChar

impl Display for Infallible

impl Display for FromBytesWithNulError

impl Display for IpAddr

impl Display for SocketAddr

impl Display for core::slice::GetDisjointMutError

impl Display for VarError

impl Display for std::fs::TryLockError

impl Display for ErrorKind

impl Display for RecvTimeoutError

impl Display for TryRecvError

impl Display for Utf8Component<'_>

impl Display for Cfg

impl Display for CfgExpr

impl Display for Platform

impl Display for ParseErrorKind

impl Display for ProfilePackageSpec

impl Display for TomlDebugInfo

impl Display for TomlTrimPaths

impl Display for TomlTrimPathsValue

impl Display for DependencyKind

impl Display for CrateType

impl Display for Edition

impl Display for TargetKind

impl Display for cargo_metadata::errors::Error

impl Display for ArtifactDebuginfo

impl Display for ObjectType

impl Display for ReferenceType

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 indexmap::GetDisjointMutError

impl Display for Level

impl Display for LevelFilter

impl Display for DeserializerError

impl Display for SerializerError

impl Display for serde_json::value::Value

impl Display for CollectionAllocErr

impl Display for time::error::Error

impl Display for Format

impl Display for InvalidFormatDescription

impl Display for Parse

impl Display for ParseFromDescription

impl Display for TryFromParsed

impl Display for Month

impl Display for Weekday

impl Display for tinystr::error::ParseError

impl Display for toml::value::Value

impl Display for Offset

impl Display for Item

impl Display for toml_edit::ser::Error

impl Display for toml_edit::value::Value

impl Display for DateTimeError

impl Display for tz::error::Error

impl Display for TzError

impl Display for ParseDataError

impl Display for TzFileError

impl Display for TzStringError

impl Display for LocalTimeTypeError

impl Display for TimeZoneError

impl Display for TransitionRuleError

impl Display for NowError

impl Display for url::parser::ParseError

impl Display for SyntaxViolation

impl Display for StrContext

Trait Display