Trait Debug

1.0.0 · Source

pub trait Debug {
    // Required method
    fn fmt(&self, f: &mut Formatter<'_>) -> Result<(), Error> ⓘ;
}

Expand description

core ? formatting.

Re-exported from core::fmt:: .

? formatting.

Debug should format the output in a programmer-facing, debugging context.

Generally speaking, you should just derive a Debug implementation.

When used with the alternate format specifier #?, the output is pretty-printed.

For more information on formatters, see the module-level documentation.

This trait can be used with #[derive] if all fields implement Debug. When derived for structs, it will use the name of the struct, then {, then a comma-separated list of each field’s name and Debug value, then }. For enums, it will use the name of the variant and, if applicable, (, then the Debug values of the fields, then ).

§Stability

Derived Debug formats are not stable, and so may change with future Rust versions. Additionally, Debug implementations of types provided by the standard library (std, core, alloc, etc.) are not stable, and may also change with future Rust versions.

§Examples

Deriving an implementation:

#[derive(Debug)]
struct Point {
    x: i32,
    y: i32,
}

let origin = Point { x: 0, y: 0 };

assert_eq!(
    format!("The origin is: {origin:?}"),
    "The origin is: Point { x: 0, y: 0 }",
);

Manually implementing:

use std::fmt;

struct Point {
    x: i32,
    y: i32,
}

impl fmt::Debug for Point {
    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
        f.debug_struct("Point")
         .field("x", &self.x)
         .field("y", &self.y)
         .finish()
    }
}

let origin = Point { x: 0, y: 0 };

assert_eq!(
    format!("The origin is: {origin:?}"),
    "The origin is: Point { x: 0, y: 0 }",
);

There are a number of helper methods on the Formatter struct to help you with manual implementations, such as debug_struct.

Types that do not wish to use the standard suite of debug representations provided by the Formatter trait (debug_struct, debug_tuple, debug_list, debug_set, debug_map) can do something totally custom by manually writing an arbitrary representation to the Formatter.

impl fmt::Debug for Point {
    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
        write!(f, "Point [{} {}]", self.x, self.y)
    }
}

Debug implementations using either derive or the debug builder API on Formatter support pretty-printing using the alternate flag: {:#?}.

Pretty-printing with #?:

#[derive(Debug)]
struct Point {
    x: i32,
    y: i32,
}

let origin = Point { x: 0, y: 0 };

let expected = "The origin is: Point {
    x: 0,
    y: 0,
}";
assert_eq!(format!("The origin is: {origin:#?}"), expected);

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::Debug for Position {
    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
        f.debug_tuple("")
         .field(&self.longitude)
         .field(&self.latitude)
         .finish()
    }
}

let position = Position { longitude: 1.987, latitude: 2.983 };
assert_eq!(format!("{position:?}"), "(1.987, 2.983)");

assert_eq!(format!("{position:#?}"), "(
    1.987,
    2.983,
)");

Trait DebugCopy item path

§Stability

§Examples

Required Methods§

fn fmt(&self, f: &mut Formatter<'_>) -> Result<(), Error> ⓘ

§Errors

§Examples

Implementors§

impl Debug for devela::_core::ascii::Char

impl Debug for DebugAsHex

impl Debug for devela::_core::fmt::Sign

impl Debug for IpAddr

impl Debug for Ipv6MulticastScope

impl Debug for devela::_core::net::SocketAddr

impl Debug for GetManyMutError

impl Debug for SearchStep

impl Debug for TryReserveErrorKind

impl Debug for VarError

impl Debug for devela::_dep::_std::io::SeekFrom

impl Debug for devela::_dep::_std::net::Shutdown

impl Debug for AncillaryError

impl Debug for BacktraceStyle

impl Debug for RecvTimeoutError

impl Debug for TryRecvError

impl Debug for devela::_dep::bumpalo::collections::CollectionAllocErr

impl Debug for CheckedCastError

impl Debug for PodCastError

impl Debug for devela::_dep::crossterm::event::Event

impl Debug for devela::_dep::crossterm::event::KeyCode

impl Debug for KeyEventKind

impl Debug for MediaKeyCode

impl Debug for ModifierKeyCode

impl Debug for devela::_dep::crossterm::event::MouseButton

impl Debug for MouseEventKind

impl Debug for Attribute

impl Debug for Color

impl Debug for Colored

impl Debug for ClearType

impl Debug for devela::_dep::hashbrown::TryReserveError

impl Debug for Era

impl Debug for devela::_dep::jiff::civil::Weekday

impl Debug for RoundMode

impl Debug for Unit

impl Debug for Designator

impl Debug for devela::_dep::jiff::fmt::friendly::Direction

impl Debug for FractionalUnit

impl Debug for Spacing

impl Debug for Meridiem

impl Debug for PiecesOffset

impl Debug for AmbiguousOffset

impl Debug for Disambiguation

impl Debug for Dst

impl Debug for OffsetConflict

impl Debug for devela::_dep::kira::backend::cpal::Error

impl Debug for ClockSpeed

impl Debug for DistortionKind

impl Debug for EqFilterKind

impl Debug for devela::_dep::kira::effect::filter::FilterMode

impl Debug for Easing

impl Debug for StartTime

impl Debug for WhenToStart

impl Debug for Waveform

impl Debug for EndPosition

impl Debug for FromFileError

impl Debug for PlaybackPosition

impl Debug for PlaybackState

impl Debug for TrackPlaybackState

impl Debug for devela::_dep::log::Level

impl Debug for devela::_dep::log::LevelFilter

impl Debug for PrefilterConfig

impl Debug for ConnectErrorKind

impl Debug for Ignore

impl Debug for PortInfoError

impl Debug for devela::_dep::midir::SendError

impl Debug for AppleGfxApi

impl Debug for LinuxBackend

impl Debug for LinuxX11Gl

impl Debug for WebGLVersion

impl Debug for Backend

impl Debug for BlendFactor

Trait Debug