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 Code

impl Debug for CheckTxKind

impl Debug for ApplySnapshotChunkResult

impl Debug for tendermint::abci::response::OfferSnapshot

impl Debug for tendermint::abci::response::ProcessProposal

impl Debug for tendermint::abci::response::VerifyVoteExtension

impl Debug for BlockSignatureInfo

impl Debug for MisbehaviorKind

impl Debug for tendermint::block::commit_sig::CommitSig

impl Debug for tendermint::block::BlockIdFlag

impl Debug for tendermint::crypto::signature::Error

impl Debug for ErrorDetail

impl Debug for tendermint::evidence::Evidence

impl Debug for tendermint::hash::Algorithm

impl Debug for Hash

impl Debug for TxIndexStatus

impl Debug for tendermint::proposal::Type

impl Debug for tendermint::public_key::Algorithm

impl Debug for tendermint::public_key::PublicKey

impl Debug for TendermintKey

impl Debug for tendermint::v0_34::abci::request::ConsensusRequest

impl Debug for tendermint::v0_34::abci::request::InfoRequest

impl Debug for tendermint::v0_34::abci::request::MempoolRequest

impl Debug for tendermint::v0_34::abci::request::Request

impl Debug for tendermint::v0_34::abci::request::SnapshotRequest

impl Debug for tendermint::v0_34::abci::response::ConsensusResponse

impl Debug for tendermint::v0_34::abci::response::InfoResponse

impl Debug for tendermint::v0_34::abci::response::MempoolResponse

impl Debug for tendermint::v0_34::abci::response::Response

impl Debug for tendermint::v0_34::abci::response::SnapshotResponse

impl Debug for tendermint::v0_37::abci::request::ConsensusRequest

impl Debug for tendermint::v0_37::abci::request::InfoRequest

impl Debug for tendermint::v0_37::abci::request::MempoolRequest

impl Debug for tendermint::v0_37::abci::request::Request

impl Debug for tendermint::v0_37::abci::request::SnapshotRequest

impl Debug for tendermint::v0_37::abci::response::ConsensusResponse

impl Debug for tendermint::v0_37::abci::response::InfoResponse

impl Debug for tendermint::v0_37::abci::response::MempoolResponse

impl Debug for tendermint::v0_37::abci::response::Response

impl Debug for tendermint::v0_37::abci::response::SnapshotResponse

impl Debug for tendermint::v0_38::abci::request::ConsensusRequest

impl Debug for tendermint::v0_38::abci::request::InfoRequest

impl Debug for tendermint::v0_38::abci::request::MempoolRequest

impl Debug for tendermint::v0_38::abci::request::Request

impl Debug for tendermint::v0_38::abci::request::SnapshotRequest

impl Debug for tendermint::v0_38::abci::response::ConsensusResponse

impl Debug for tendermint::v0_38::abci::response::InfoResponse

impl Debug for tendermint::v0_38::abci::response::MempoolResponse

impl Debug for tendermint::v0_38::abci::response::Response

impl Debug for tendermint::v0_38::abci::response::SnapshotResponse

impl Debug for tendermint::vote::Type

impl Debug for tendermint::consensus::state::Ordering

impl Debug for tendermint::consensus::state::fmt::Alignment

impl Debug for DebugAsHex

impl Debug for Sign

impl Debug for TryReserveErrorKind

impl Debug for AsciiChar

impl Debug for Infallible

impl Debug for c_void

impl Debug for IpAddr

impl Debug for Ipv6MulticastScope

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

impl Debug for FpCategory

impl Debug for IntErrorKind

impl Debug for GetManyMutError

impl Debug for SearchStep

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

impl Debug for BacktraceStatus

impl Debug for VarError

impl Debug for SeekFrom

impl Debug for ErrorKind

impl Debug for Shutdown

Trait Debug