Trait Display

1.6.0 · 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 !

impl Display for Aarch64Architecture

impl Display for AccessError

impl Display for AddrParseError

impl Display for AllocError

impl Display for Architecture

impl Display for Arguments<'_>

impl Display for ArmArchitecture

impl Display for ArrayType

impl Display for AsciiChar

impl Display for Backtrace

impl Display for BinaryFormat

impl Display for BinaryReaderError

impl Display for BorrowError

impl Display for BorrowMutError

impl Display for BuildMetadata

impl Display for ByteStr

impl Display for ByteString

impl Display for CharTryFromError

impl Display for CleverArchitecture

impl Display for CollectionAllocErr

impl Display for Collector

impl Display for ColorChoiceParseError

impl Display for Comparator

impl Display for CompileError

impl Display for ComponentName

impl Display for ComponentPC

impl Display for CompositeInnerType

impl Display for CompositeType

impl Display for ContType

impl Display for ConvertError

impl Display for DecodeError

impl Display for DecodeUtf16Error

impl Display for DestBufTooSmallError

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

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

impl Display for DwAccess

impl Display for DwAddr

impl Display for DwAt

impl Display for DwAte

impl Display for DwCc

impl Display for DwCfa

impl Display for DwChildren

impl Display for DwDefaulted

impl Display for DwDs

impl Display for DwDsc

impl Display for DwEhPe

impl Display for DwEnd

impl Display for DwForm

impl Display for DwId

impl Display for DwIdx

impl Display for DwInl

impl Display for DwLang

impl Display for DwLle

impl Display for DwLnct

impl Display for DwLne

impl Display for DwLns

impl Display for DwMacinfo

impl Display for DwMacro

impl Display for DwOp

impl Display for DwOrd

impl Display for DwRle

impl Display for DwSect

impl Display for DwSectV2

impl Display for DwTag

impl Display for DwUt

impl Display for DwVirtuality

impl Display for DwVis

impl Display for EngineOrModuleTypeIndex

Trait Display