Trait Debug

1.36.0 · Source

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

Expand description

? 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,
)");

Debug

Trait Debug Copy item path

§Stability

§Examples

Required Methods§

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

§Errors

§Examples

Implementors§

impl Debug for AsciiChar

impl Debug for comfy_wgpu::bytemuck::__core::cmp::Ordering

impl Debug for Infallible

impl Debug for FromBytesWithNulError

impl Debug for c_void

impl Debug for AtomicOrdering

impl Debug for SimdAlign

impl Debug for IpAddr

impl Debug for Ipv6MulticastScope

impl Debug for comfy_wgpu::bytemuck::__core::net::SocketAddr

impl Debug for FpCategory

impl Debug for IntErrorKind

impl Debug for comfy_wgpu::bytemuck::__core::sync::atomic::Ordering

impl Debug for CheckedCastError

impl Debug for PodCastError

impl Debug for Month

impl Debug for RoundingError

impl Debug for SecondsFormat

impl Debug for Weekday

impl Debug for Colons

impl Debug for comfy_wgpu::chrono::format::Fixed

impl Debug for Numeric

impl Debug for OffsetPrecision

impl Debug for Pad

impl Debug for ParseErrorKind

impl Debug for Verbosity

impl Debug for comfy_wgpu::color_backtrace::termcolor::Color

impl Debug for ColorChoice

impl Debug for comfy_wgpu::crossbeam::channel::RecvTimeoutError

impl Debug for comfy_wgpu::crossbeam::channel::TryRecvError

impl Debug for Side

impl Debug for TopBottomSide

impl Debug for ScrollBarVisibility

impl Debug for AboveOrBelow

impl Debug for comfy_wgpu::egui::Align

impl Debug for CursorGrab

impl Debug for comfy_wgpu::egui::CursorIcon

impl Debug for comfy_wgpu::egui::Direction

impl Debug for comfy_wgpu::egui::Event

impl Debug for FontFamily

impl Debug for IMEPurpose

impl Debug for ImageFit

impl Debug for comfy_wgpu::egui::Key

impl Debug for MouseWheelUnit

impl Debug for Order

impl Debug for PointerButton

impl Debug for comfy_wgpu::egui::ResizeDirection

impl Debug for comfy_wgpu::egui::Shape

impl Debug for SystemTheme

impl Debug for TextStyle

impl Debug for TextureFilter

impl Debug for TextureId

impl Debug for TextureWrapMode

impl Debug for comfy_wgpu::egui::TouchPhase

impl Debug for comfy_wgpu::egui::UserAttentionType

impl Debug for ViewportCommand

impl Debug for ViewportEvent

impl Debug for WidgetType

impl Debug for comfy_wgpu::egui::WindowLevel

impl Debug for comfy_wgpu::egui::load::Bytes

impl Debug for comfy_wgpu::egui::load::LoadError

impl Debug for OperatingSystem

impl Debug for OutputEvent

impl Debug for HandleShape

impl Debug for NumericColorSpace

impl Debug for comfy_wgpu::egui_plot::Axis

impl Debug for Corner

impl Debug for HPlacement

impl Debug for comfy_wgpu::egui_plot::LineStyle

impl Debug for MarkerShape

impl Debug for Orientation

Trait Debug