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 CreationStrategy

impl Debug for FactoryResourceSpecifier

impl Debug for DumpManifestError

impl Debug for AbortReason

impl Debug for AcceptedLedgerTransactionKind

impl Debug for AccessControllerError

impl Debug for AccessControllerPartitionOffset

impl Debug for AccessRule

impl Debug for AccountLockerPartitionOffset

impl Debug for AccountPartitionOffset

impl Debug for Actor

impl Debug for AddressBech32DecodeError

impl Debug for AddressBech32EncodeError

impl Debug for AllowedIds

impl Debug for AlwaysVisibleGlobalNodesVersion

impl Debug for AnyTransaction

impl Debug for ApplicationError

impl Debug for AttachedModuleId

impl Debug for AuthError

impl Debug for AuthZoneError

impl Debug for AuthZoneField

impl Debug for BalanceChange

impl Debug for BasicRequirement

impl Debug for BatchPartitionStateUpdate

impl Debug for BlueprintPartitionType

impl Debug for BlueprintPayloadDef

impl Debug for BlueprintPayloadIdentifier

impl Debug for BlueprintType

impl Debug for BootLoaderField

impl Debug for BootloadingError

impl Debug for BucketError

impl Debug for BucketSnapshot

impl Debug for CallFrameDrainSubstatesError

impl Debug for CallFrameError

impl Debug for CallFrameRemoveSubstateError

impl Debug for CallFrameScanKeysError

impl Debug for CallFrameScanSortedSubstatesError

impl Debug for CallFrameSetSubstateError

impl Debug for CannotGlobalizeError

impl Debug for ChildNames

impl Debug for CloseSubstateError

impl Debug for CloseSubstateEvent

impl Debug for ComponentField

impl Debug for ComponentRoyaltyPartitionOffset

impl Debug for ComposeProofError

impl Debug for CompositeRequirement

impl Debug for ConsensusManagerCollection

impl Debug for ConsensusManagerConfigurationVersions

impl Debug for ConsensusManagerCurrentProposalStatisticVersions

impl Debug for ConsensusManagerCurrentValidatorSetVersions

impl Debug for ConsensusManagerError

impl Debug for ConsensusManagerFeature

impl Debug for ConsensusManagerField

impl Debug for ConsensusManagerPartitionOffset

impl Debug for ConsensusManagerProposerMilliTimestampVersions

impl Debug for ConsensusManagerProposerMinuteTimestampVersions

impl Debug for ConsensusManagerRegisteredValidatorByStakeVersions

impl Debug for ConsensusManagerStateVersions

impl Debug for ConsensusManagerTypedFieldSubstateValue

impl Debug for ConsensusManagerTypedSubstateKey

impl Debug for ConsensusManagerTypedSubstateValue

impl Debug for ConsensusManagerValidatorRewardsVersions

impl Debug for ContentValidationError

impl Debug for CostingError

impl Debug for CreateFrameError

impl Debug for CreateNodeError

impl Debug for CreateObjectError

impl Debug for CurveType

impl Debug for DatabaseUpdate

impl Debug for DateTimeError

impl Debug for DecodeError

impl Debug for DecryptorsByCurve

Trait Debug