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 DbError

impl Display for ExecutorError

impl Display for icydb_core::db::query::QueryError

impl Display for QueryPlan

impl Display for SaveMode

impl Display for ResponseError

impl Display for StoreError

impl Display for icydb_core::Error

impl Display for InterfaceError

impl Display for icydb_core::interface::query::QueryError

impl Display for Key

impl Display for icydb_core::serialize::SerializeError

impl Display for icydb_core::types::PrincipalError

impl Display for UlidError

impl Display for AsciiChar

impl Display for Infallible

impl Display for FromBytesWithNulError

impl Display for IpAddr

impl Display for SocketAddr

impl Display for GetDisjointMutError

impl Display for VarError

impl Display for std::fs::TryLockError

impl Display for ErrorKind

impl Display for RecvTimeoutError

impl Display for TryRecvError

impl Display for binread::error::Error

impl Display for candid::error::Error

impl Display for candid::types::internal::Label

impl Display for TypeInner

impl Display for MemoryRegistryError

impl Display for canic_memory::serialize::SerializeError

impl Display for Case

impl Display for RoundingError

impl Display for chrono::weekday::Weekday

impl Display for DecodeKind

impl Display for BinaryError

impl Display for FromHexError

impl Display for CanisterSigError

impl Display for SignCostError

impl Display for CallFailed

impl Display for ic_cdk::call::Error

impl Display for OnewayError

impl Display for SignCallError

impl Display for StableMemoryError

impl Display for ErrorCode

impl Display for RejectCode

impl Display for ic_stable_structures::base_vec::InitError

impl Display for ic_stable_structures::base_vec::InitError

impl Display for ic_stable_structures::cell::InitError

impl Display for ic_stable_structures::cell::InitError

impl Display for ic_stable_structures::log::InitError

impl Display for ic_stable_structures::log::InitError

impl Display for ic_principal::PrincipalError

impl Display for ICRC1TextReprError

impl Display for TransferError

impl Display for ApproveError

impl Display for TransferFromError

impl Display for AccountOrId

impl Display for Icrc21Function

impl Display for ICRC3Value

impl Display for Value

impl Display for ValuePredicateFailures

impl Display for leb128::read::Error

impl Display for minicbor::data::Type

impl Display for rust_decimal::error::Error

impl Display for CollectionAllocErr

impl Display for strum::ParseError

impl Display for time::error::Error

impl Display for Format

impl Display for InvalidFormatDescription

Trait Display