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,
)");

Trait DebugCopy item path

§Stability

§Examples

Required Methods§

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

§Errors

§Examples

Implementors§

impl Debug for equix::err::Error

impl Debug for fs_mistrust::err::Error

impl Debug for TrustedGroup

impl Debug for TrustedUser

impl Debug for hashx::Runtime

impl Debug for RuntimeOption

impl Debug for CompilerError

impl Debug for hashx::err::Error

impl Debug for safelog::err::Error

impl Debug for ErasedSinkTrySendError

impl Debug for tor_basic_utils::n_key_list::Error

impl Debug for tor_basic_utils::n_key_set::Error

impl Debug for tor_basic_utils::test_rng::Config

impl Debug for tor_bytes::err::EncodeError

impl Debug for tor_bytes::err::Error

impl Debug for AnyChanMsg

impl Debug for tor_cell::err::Error

impl Debug for RelayCellFormat

impl Debug for CircRequestExt

impl Debug for CircResponseExt

impl Debug for XonKbpsEwma

impl Debug for IntroEstablishedExt

impl Debug for EstablishIntroSigError

impl Debug for OnionKey

impl Debug for ProofOfWork

impl Debug for IpVersionPreference

impl Debug for ResolvedVal

impl Debug for tor_cell::relaycell::udp::Address

impl Debug for tor_cert::CertifiedKey

impl Debug for Ed25519CertConstructorError

impl Debug for CertEncodeError

impl Debug for CertError

impl Debug for ChanProvenance

impl Debug for ChannelUsage

impl Debug for Dormancy

impl Debug for tor_chanmgr::err::Error

impl Debug for ConnBlockage

impl Debug for tor_chanmgr::transport::proxied::Protocol

impl Debug for ProxyError

impl Debug for TimeValidityError

impl Debug for tor_circmgr::err::Error

impl Debug for StreamIsolationBuilderError

impl Debug for tor_circmgr::timeouts::Action

impl Debug for ConfigError

impl Debug for ExtendStrategy

impl Debug for tor_config::file_watcher::Event

impl Debug for FileWatcherBuildError

impl Debug for InvalidListen

impl Debug for ConfigResolveError

impl Debug for BoolOrAuto

impl Debug for PaddingLevel

impl Debug for ConfigurationSource

impl Debug for MustRead

impl Debug for CfgAddrError

impl Debug for CfgPathError

impl Debug for AnonymizedRequest

impl Debug for RequestError

impl Debug for AbsRetryTime

impl Debug for RetryTime

impl Debug for tor_general_addr::general::AddrParseError

impl Debug for tor_general_addr::general::SocketAddr

impl Debug for tor_geoip::err::Error

impl Debug for BridgeParseError

impl Debug for BridgeDescEvent

impl Debug for ExternalActivity

impl Debug for GuardRestriction

impl Debug for GuardUsageKind

impl Debug for RetireCircuits

impl Debug for VanguardMode

impl Debug for GuardMgrConfigError

impl Debug for GuardMgrError

impl Debug for PickGuardError

Trait Debug