Trait 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 DebugCopy item path

§Stability

§Examples

Required Methods§

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

§Errors

§Examples

Implementors§

impl Debug for AsciiChar

impl Debug for origin_studio::cmp::Ordering

impl Debug for TryReserveErrorKind

impl Debug for Infallible

impl Debug for VarError

impl Debug for origin_studio::io::SeekFrom

impl Debug for IpAddr

impl Debug for Ipv6MulticastScope

impl Debug for SocketAddr

impl Debug for FpCategory

impl Debug for IntErrorKind

impl Debug for GetDisjointMutError

impl Debug for SearchStep

impl Debug for origin_studio::sync::atomic::Ordering

impl Debug for origin_studio::fmt::Alignment

impl Debug for DebugAsHex

impl Debug for Sign

impl Debug for FromBytesWithNulError

impl Debug for c_void

impl Debug for DwarfFileType

impl Debug for Format

impl Debug for SectionId

impl Debug for Vendor

impl Debug for RunTimeEndian

impl Debug for Pointer

impl Debug for gimli::read::Error

impl Debug for IndexSectionId

impl Debug for Value

impl Debug for ValueType

impl Debug for fsconfig_command

impl Debug for membarrier_cmd

impl Debug for membarrier_cmd_flag

impl Debug for procmap_query_flags

impl Debug for rustix::backend::fs::types::Advice

impl Debug for FileType

impl Debug for FlockOperation

impl Debug for rustix::backend::mm::types::Advice

impl Debug for Resource

impl Debug for MembarrierCommand

impl Debug for TimerfdClockId

impl Debug for ClockId

impl Debug for rustix::fs::seek_from::SeekFrom

impl Debug for Direction

impl Debug for DumpableBehavior

impl Debug for EndianMode

impl Debug for FloatingPointMode

impl Debug for MachineCheckMemoryCorruptionKillPolicy

impl Debug for PTracer

impl Debug for SpeculationFeature

impl Debug for TimeStampCounterReadability

impl Debug for TimingMethod

impl Debug for VirtualMemoryMapAddress

impl Debug for FlockOffsetType

impl Debug for FlockType

impl Debug for NanosleepRelativeResult

impl Debug for WakeOp

impl Debug for WakeOpCmp

impl Debug for Capability

impl Debug for CoreSchedulingScope

impl Debug for SecureComputingMode

impl Debug for SysCallUserDispatchFastSwitch

impl Debug for LinkNameSpaceType

impl Debug for Always

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

Trait Debug