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".

Implementors§

1.100.0 · Source§

impl Display for !

1.26.0 · Source§

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 AccessError

impl Display for AcquireError

impl Display for AddrParseError

impl Display for AllocError

impl Display for Arg

impl Display for Arguments<'_>

impl Display for AsciiChar

impl Display for Ast

impl Display for http_type::attribute::enum::Attribute

impl Display for icu_locale_core::extensions::unicode::attribute::Attribute

impl Display for xml::attribute::Attribute<'_>

impl Display for Attributes

impl Display for BStr

impl Display for BString

impl Display for Backtrace

impl Display for BernoulliError

impl Display for BorrowError

impl Display for BorrowMutError

impl Display for Buffer

impl Display for regex_automata::dfa::onepass::BuildError

impl Display for regex_automata::hybrid::error::BuildError

impl Display for regex_automata::meta::error::BuildError

impl Display for regex_automata::nfa::thompson::error::BuildError

impl Display for aho_corasick::util::error::BuildError

impl Display for ByteStr

impl Display for ByteString

impl Display for winnow::stream::bytes::Bytes

impl Display for winnow::stream::bytes::Bytes

impl Display for CacheError

impl Display for CaseFoldError

impl Display for CharTryFromError

impl Display for CollectionAllocErr

impl Display for Color

impl Display for ColorChoice

impl Display for ColorType

impl Display for Command

impl Display for Compress

impl Display for CompressError

impl Display for Context

impl Display for ContextError

impl Display for ContextKind

impl Display for ContextValue

impl Display for CurrencyType

impl Display for DataError

impl Display for DataErrorKind

impl Display for DataIdentifierBorrowed<'_>

impl Display for DataLocale

impl Display for Date

impl Display for Datetime

impl Display for DatetimeParseError

impl Display for DeFloat<'_>

impl Display for DeInteger<'_>

impl Display for DecodeUtf16Error

impl Display for flate2::mem::DecompressError

impl Display for miniz_oxide::inflate::DecompressError

impl Display for DefaultServerHook

impl Display for DeserializeError

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

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

impl Display for Elapsed

impl Display for EmitterError

impl Display for Empty

impl Display for EmptyError

impl Display for Encoding

impl Display for Errno

impl Display for euv_cli::IoError

impl Display for core::fmt::Error

impl Display for rand::distr::uniform::Error

Trait Display