Trait Debug

1.6.0 · 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 Action

impl Debug for ClientApiHint

impl Debug for ColorEditDisplayMode

impl Debug for ColorEditInputMode

impl Debug for ColorFormat

impl Debug for ColorPickerMode

impl Debug for ColorPreview

impl Debug for ComboBoxHeight

impl Debug for ComboBoxPreviewMode

impl Debug for Condition

impl Debug for ContextCreationApi

impl Debug for ContextReleaseBehavior

impl Debug for ContextRobustnessHint

impl Debug for CursorMode

impl Debug for Direction

impl Debug for chaos_framework::Error

impl Debug for EulerRot

impl Debug for FocusedWidget

impl Debug for GamepadAxis

impl Debug for GamepadButton

impl Debug for HistoryDirection

impl Debug for InitError

impl Debug for InitHint

impl Debug for ItemFlag

impl Debug for JoystickEvent

impl Debug for JoystickId

impl Debug for MonitorEvent

impl Debug for MouseCursor

impl Debug for NavInput

impl Debug for OpenGlProfileHint

impl Debug for ProjectionType

impl Debug for StandardCursor

impl Debug for StyleColor

impl Debug for StyleVar

impl Debug for SwapInterval

impl Debug for WindowEvent

impl Debug for WindowHint

impl Debug for GLFWcursor

impl Debug for GLFWmonitor

impl Debug for GLFWwindow

impl Debug for DataType

impl Debug for c_void

impl Debug for AsciiChar

impl Debug for chaos_framework::__core::cmp::Ordering

impl Debug for Infallible

impl Debug for FromBytesWithNulError

impl Debug for AtomicOrdering

impl Debug for SimdAlign

impl Debug for IpAddr

impl Debug for Ipv6MulticastScope

impl Debug for chaos_framework::__core::net::SocketAddr

impl Debug for FpCategory

impl Debug for IntErrorKind

impl Debug for GetDisjointMutError

impl Debug for SearchStep

impl Debug for chaos_framework::__core::sync::atomic::Ordering

impl Debug for chaos_framework::__core::fmt::Alignment

impl Debug for DebugAsHex

impl Debug for chaos_framework::__core::fmt::Sign

impl Debug for TryReserveErrorKind

impl Debug for BacktraceStatus

impl Debug for VarError

impl Debug for std::fs::TryLockError

impl Debug for SeekFrom

impl Debug for std::io::error::ErrorKind

impl Debug for Shutdown

impl Debug for AncillaryError

impl Debug for BacktraceStyle

impl Debug for RecvTimeoutError

impl Debug for TryRecvError

impl Debug for aligned_vec::TryReserveError

Trait Debug