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 Approximation

impl Debug for AxisOp

impl Debug for Cost

impl Debug for DatumType

impl Debug for InOut

impl Debug for QParams

impl Debug for RValue

impl Debug for TDim

impl Debug for TValue

impl Debug for TypeName

impl Debug for Validation

impl Debug for Value

impl Debug for PadMode

impl Debug for KernelFormat

impl Debug for PaddingSpec

impl Debug for Comp

impl Debug for ModePicker

impl Debug for ProtoFusedSpec

impl Debug for tract_pulse::internal::tract_core::ops::nn::DataFormat

impl Debug for Reducer

impl Debug for SoftmaxExp

impl Debug for TooEarly

impl Debug for GetDisjointMutError

impl Debug for SearchStep

impl Debug for CollectionAllocErr

impl Debug for tract_pulse::internal::tract_core::ops::nn::tract_data::prelude::tract_itertools::Position

impl Debug for AsciiChar

impl Debug for BacktraceStatus

impl Debug for tract_pulse::internal::tract_core::ops::nn::tract_downcast_rs::__std::cmp::Ordering

impl Debug for TryReserveErrorKind

impl Debug for Infallible

impl Debug for VarError

impl Debug for FromBytesWithNulError

impl Debug for c_void

impl Debug for tract_pulse::internal::tract_core::ops::nn::tract_downcast_rs::__std::fs::TryLockError

impl Debug for tract_pulse::internal::tract_core::ops::nn::tract_downcast_rs::__std::io::ErrorKind

impl Debug for tract_pulse::internal::tract_core::ops::nn::tract_downcast_rs::__std::io::SeekFrom

impl Debug for IpAddr

impl Debug for Ipv6MulticastScope

impl Debug for Shutdown

impl Debug for tract_pulse::internal::tract_core::ops::nn::tract_downcast_rs::__std::net::SocketAddr

impl Debug for FpCategory

impl Debug for IntErrorKind

impl Debug for AncillaryError

impl Debug for BacktraceStyle

impl Debug for tract_pulse::internal::tract_core::ops::nn::tract_downcast_rs::__std::sync::atomic::Ordering

impl Debug for RecvTimeoutError

impl Debug for TryRecvError

impl Debug for BinOp

impl Debug for WeightType

impl Debug for ImplementationQuality

impl Debug for OutputStoreSpec

impl Debug for RoundingPolicy

impl Debug for Executor

impl Debug for tract_pulse::internal::tract_core::ops::nn::tract_ndarray::ErrorKind

impl Debug for Order

impl Debug for SliceInfoElem

impl Debug for FloatErrorKind

impl Debug for InputMapping

impl Debug for tract_pulse::internal::fmt::Alignment

impl Debug for DebugAsHex

impl Debug for tract_pulse::internal::fmt::Sign

impl Debug for AhoCorasickKind

impl Debug for aho_corasick::packed::api::MatchKind

impl Debug for aho_corasick::util::error::MatchErrorKind

impl Debug for Candidate

impl Debug for aho_corasick::util::search::Anchored

impl Debug for aho_corasick::util::search::MatchKind

impl Debug for StartKind

impl Debug for BigEndian

impl Debug for LittleEndian

impl Debug for FlushCompress

Trait Debug