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, }),
);

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 DecodeError

impl Display for hashbrown::TryReserveError

impl Display for indexmap::GetDisjointMutError

impl Display for Level

impl Display for LevelFilter

impl Display for postcard::error::Error

impl Display for CollectionAllocErr

impl Display for target_lexicon::parse_error::ParseError

impl Display for Aarch64Architecture

impl Display for Architecture

impl Display for ArmArchitecture

impl Display for BinaryFormat

impl Display for Environment

impl Display for Mips32Architecture

impl Display for Mips64Architecture

impl Display for OperatingSystem

impl Display for Riscv32Architecture

impl Display for Riscv64Architecture

impl Display for Vendor

impl Display for X86_32Architecture

impl Display for BigEndian

impl Display for LittleEndian

impl Display for CompileError

impl Display for EngineOrModuleTypeIndex

impl Display for FlagValue<'_>

impl Display for Trap

impl Display for WasmCompositeType

impl Display for WasmError

impl Display for WasmHeapType

impl Display for WasmStorageType

impl Display for WasmValType

impl Display for PrimitiveValType

impl Display for StorageType

impl Display for UnpackedIndex

impl Display for ValType

impl Display for AsciiChar

impl Display for Infallible

impl Display for FromBytesWithNulError

impl Display for IpAddr

impl Display for SocketAddr

impl Display for wasmtime_environ::__core::slice::GetDisjointMutError

impl Display for VarError

impl Display for std::fs::TryLockError

impl Display for ErrorKind

impl Display for std::sync::mpsc::RecvTimeoutError

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

impl Display for bool

impl Display for char

impl Display for f16

impl Display for f32

impl Display for f64

impl Display for i8

impl Display for i16

impl Display for i32

impl Display for i64

impl Display for i128

impl Display for isize

impl Display for !

impl Display for str

impl Display for u8

impl Display for u16

impl Display for u32

impl Display for u64

impl Display for u128

impl Display for usize

impl Display for anyhow::Error

impl Display for bitflags::parser::ParseError

impl Display for DestBufTooSmallError

impl Display for getrandom::error::Error

impl Display for indexmap::TryReserveError

Trait Display