Trait devela::_libstd::fmt::Debug

1.0.0 · 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,
)");

Trait devela::_libstd::fmt::DebugCopy item path

§Stability

§Examples

Required Methods§

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

§Errors

§Examples

Implementors§

impl Debug for CheckedCastError

impl Debug for PodCastError

impl Debug for devela::_deps::hashbrown::TryReserveError

impl Debug for Level

impl Debug for LevelFilter

impl Debug for PrefilterConfig

impl Debug for GraphemeIncomplete

impl Debug for NeverOk

impl Debug for DataError

impl Debug for NumError

impl Debug for Sign

impl Debug for AngleDirection

impl Debug for AngleKind

impl Debug for devela::text::AsciiChar

impl Debug for TextError

impl Debug for Month

impl Debug for TimeError

impl Debug for Weekday

impl Debug for devela::_libstd::ascii::Char

impl Debug for BacktraceStatus

impl Debug for devela::_libstd::cmp::Ordering

impl Debug for TryReserveErrorKind

impl Debug for Infallible

impl Debug for VarError

impl Debug for c_void

impl Debug for ErrorKind

impl Debug for SeekFrom

impl Debug for IpAddr

impl Debug for Ipv6MulticastScope

impl Debug for Shutdown

impl Debug for devela::_libstd::net::SocketAddr

impl Debug for FpCategory

impl Debug for IntErrorKind

impl Debug for AncillaryError

impl Debug for BacktraceStyle

impl Debug for SearchStep

impl Debug for devela::_libstd::sync::atomic::Ordering

impl Debug for RecvTimeoutError

impl Debug for TryRecvError

impl Debug for devela::_libstd::fmt::Alignment

impl Debug for _Unwind_Reason_Code

impl Debug for bool

impl Debug for char

impl Debug for f16

impl Debug for f32

impl Debug for f64

impl Debug for f128

impl Debug for i8

impl Debug for i16

impl Debug for i32

impl Debug for i64

impl Debug for i128

impl Debug for isize

impl Debug for !

impl Debug for str

impl Debug for u8

impl Debug for u16

impl Debug for u32

impl Debug for u64

impl Debug for u128

impl Debug for ()

impl Debug for usize

impl Debug for ParseLevelError

impl Debug for SetLoggerError

impl Debug for One

impl Debug for Three

impl Debug for Two

impl Debug for devela::_deps::memchr::arch::all::packedpair::Finder

impl Debug for Pair

impl Debug for devela::_deps::memchr::arch::all::rabinkarp::Finder

impl Debug for devela::_deps::memchr::arch::all::rabinkarp::FinderRev

impl Debug for devela::_deps::memchr::arch::all::shiftor::Finder

Trait devela::_libstd::fmt::Debug