Trait Debug

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1.0.0 · Source

pub(crate) 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,
)");

Implementors§

Source §

impl Debug for AnonymizedRequest

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impl Debug for RequestError

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impl Debug for DirectoryKeyProviderError

impl Debug for untrusted::input::Input<'_>

The value is intentionally omitted from the output to avoid leaking secrets.

Source §

impl Debug for EndOfInput

Source §

impl Debug for untrusted::reader::Reader<'_>

Avoids writing the value or position to avoid creating a side channel, though Reader can’t avoid leaking the position via timing.

Debug the serialization of this URL.

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impl<T, O> Debug for BitVec<T, O>
where T: BitStore, O: BitOrder,

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impl<T, O> Debug for Drain<'_, T, O>
where T: BitStore, O: BitOrder,

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impl<T, O> Debug for IntoIter<T, O>
where T: BitStore, O: BitOrder,

Original

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impl<T, O> Debug for Iter<'_, T, O>
where T: BitStore, O: BitOrder,

Original

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impl<T, O> Debug for IterMut<'_, T, O>
where T: BitStore, O: BitOrder,

Trait DebugCopy item path

§Stability

§Examples

Required Methods§

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

§Errors

§Examples

Implementors§

impl Debug for AnonymizedRequest

impl Debug for RequestError

impl Debug for DirectoryKeyProviderError

impl Debug for Anonymity

impl Debug for ClientError

impl Debug for UploadError

impl Debug for EstablishSessionError

impl Debug for FatalError

impl Debug for IntroRequestError

impl Debug for IptError

impl Debug for tor_hsservice::StartupError

impl Debug for IptStoreError

impl Debug for StateExpiryError

impl Debug for IptEstablisherError

impl Debug for IptStatusStatus

impl Debug for RequestDisposition

impl Debug for ChooseIptError

impl Debug for CreateIptError

impl Debug for TrackedStatus

impl Debug for IptKeyRole

impl Debug for DescriptorStatus

impl Debug for PublishStatus

impl Debug for LogContentError

impl Debug for ReplayError

impl Debug for DescUploadRetryError

impl Debug for Problem

impl Debug for tor_hsservice::status::State

impl Debug for AnyRelayMsg

impl Debug for ConfigBuildError

impl Debug for tor_hsservice::internal_prelude::DirClientError

impl Debug for tor_hsservice::internal_prelude::ErrorKind

impl Debug for HsCircKind

impl Debug for MetaCellDisposition

impl Debug for tor_hsservice::internal_prelude::Ordering

impl Debug for Reconfigure

impl Debug for ReconfigureError

impl Debug for tor_hsservice::internal_prelude::SeekFrom

impl Debug for Timeliness

impl Debug for Void

impl Debug for tor_hsservice::internal_prelude::fmt::Alignment

impl Debug for DebugAsHex

impl Debug for tor_hsservice::internal_prelude::fmt::Sign

impl Debug for tor_hsservice::internal_prelude::fs::TryLockError

impl Debug for TryReserveErrorKind

impl Debug for core::ascii::ascii_char::AsciiChar

impl Debug for Infallible

impl Debug for FromBytesWithNulError

impl Debug for c_void

impl Debug for core::net::ip_addr::IpAddr

impl Debug for Ipv6MulticastScope

impl Debug for core::net::socket_addr::SocketAddr

impl Debug for FpCategory

impl Debug for IntErrorKind

impl Debug for core::slice::GetDisjointMutError

impl Debug for SearchStep

impl Debug for core::sync::atomic::Ordering

impl Debug for BacktraceStatus

impl Debug for VarError

impl Debug for std::net::Shutdown

impl Debug for AncillaryError

impl Debug for BacktraceStyle

impl Debug for RecvTimeoutError

impl Debug for std::sync::mpsc::TryRecvError

impl Debug for TokioTpErr

impl Debug for FlushCompress

impl Debug for FlushDecompress

impl Debug for flate2::mem::Status

impl Debug for FromHexError

impl Debug for liblzma::stream::Error

impl Debug for liblzma::stream::Status

impl Debug for log::Level

impl Debug for log::LevelFilter

Trait Debug