Trait Display

1.0.0 · Source

pub(crate) 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 ASN1DateTime

impl Display for Aborted

impl Display for std::thread::local::AccessError

impl Display for async_std::task::task_local::AccessError

impl Display for AcquireError

impl Display for Action

impl Display for Actual

impl Display for core::net::parser::AddrParseError

impl Display for tor_general_addr::general::AddrParseError

impl Display for rustls_pki_types::server_name::AddrParseError

impl Display for ipnet::parser::AddrParseError

impl Display for AddrPortPattern

impl Display for Algorithm

impl Display for AlgorithmType

impl Display for AllocError

impl Display for AnyDelimiterCodecError

impl Display for ArgumentError

impl Display for Arguments<'_>

impl Display for Array

impl Display for ArrayOfTables

impl Display for ArtiPath

impl Display for ArtiPathError

impl Display for ArtiPathSyntaxError

impl Display for ArtiPathUnavailableError

impl Display for AsAsciiStrError

impl Display for core::ascii::ascii_char::AsciiChar

impl Display for ascii::ascii_char::AsciiChar

impl Display for AsciiStr

impl Display for AsciiString

impl Display for Asn1GeneralizedTimeRef

impl Display for Asn1ObjectRef

impl Display for Asn1TimeRef

impl Display for Ast

impl Display for Attribute

impl Display for AttributeTypeAndValue

impl Display for Attributes

impl Display for AuthCertVersion

impl Display for AuthKeyType

impl Display for Authority

impl Display for B16

impl Display for B64

impl Display for B16U

impl Display for winnow::stream::bstr::BStr

impl Display for winnow::stream::bstr::BStr

impl Display for bstr::bstr::BStr

impl Display for BString

impl Display for Backtrace

impl Display for BadIso8601TimeSlug

impl Display for BadSlug

impl Display for Base64Fingerprint

impl Display for rand::distr::bernoulli::BernoulliError

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

impl Display for rand::distr::bernoulli::BernoulliError

impl Display for BigEndian

impl Display for BigInt

impl Display for BigNum

impl Display for BigNumRef

impl Display for BigUint

impl Display for BinaryError

impl Display for BlindingError

impl Display for BmpString

impl Display for BorrowError

impl Display for BorrowMutError

impl Display for BridgeAddr

impl Display for BridgeAddrError

impl Display for BridgeConfig

impl Display for BridgeParseError

impl Display for Buffer

Trait Display