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 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 std::io::error::ErrorKind

impl Display for RecvTimeoutError

impl Display for std::sync::mpsc::TryRecvError

impl Display for base16ct::error::Error

impl Display for DecodeError

impl Display for base64ct::errors::Error

impl Display for bs58::alphabet::Error

impl Display for bs58::decode::Error

impl Display for bs58::encode::Error

impl Display for byte_slice_cast::Error

impl Display for const_oid::error::Error

impl Display for der::error::ErrorKind

impl Display for Class

impl Display for Tag

impl Display for TagMode

impl Display for ed25519_zebra::error::Error

impl Display for gimli::read::Error

impl Display for HexToArrayError

impl Display for HexToBytesError

impl Display for hex::error::FromHexError

impl Display for httparse::Error

impl Display for indexmap::GetDisjointMutError

impl Display for libsecp256k1_core::error::Error

impl Display for log::Level

impl Display for log::LevelFilter

impl Display for num_format::error_kind::ErrorKind

impl Display for parity_bip39::Error

impl Display for Language

impl Display for parity_wasm::elements::Error

impl Display for Instruction

impl Display for ValueType

impl Display for password_hash::errors::Error

impl Display for InvalidValue

impl Display for pkcs8::error::Error

impl Display for CommittedCandidateReceiptError

impl Display for prometheus::errors::Error

impl Display for BernoulliError

impl Display for WeightedError

impl Display for StartError

impl Display for regex_syntax::ast::Ast

impl Display for regex_syntax::ast::Ast

impl Display for regex_syntax::ast::ErrorKind

impl Display for regex_syntax::ast::ErrorKind

impl Display for regex_syntax::error::Error

impl Display for regex_syntax::error::Error

impl Display for regex_syntax::hir::ErrorKind

impl Display for regex_syntax::hir::ErrorKind

impl Display for regex::error::Error

impl Display for rustc_hex::FromHexError

impl Display for MultiSignatureStage

impl Display for SignatureError

impl Display for sec1::error::Error

impl Display for secp256k1::Error

impl Display for serde_json::value::Value

impl Display for CollectionAllocErr

impl Display for ApiError

impl Display for sp_core::address_uri::Error

impl Display for DeriveError

impl Display for PublicError

impl Display for SecretStringError

impl Display for sp_inherents::Error

impl Display for sp_keystore::Error

Trait Display