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 AccessMethod

impl Debug for AddressBit

impl Debug for AgpSlotWidth

impl Debug for BoardType

impl Debug for BootOption

impl Debug for BootOptionOnLimit

impl Debug for BusNumber

impl Debug for CacheAssociativity

impl Debug for CacheLocation

impl Debug for CacheMemorySize

impl Debug for CacheOperationalMode

impl Debug for ChassisHeight

impl Debug for ChassisLockPresence

impl Debug for ChassisSecurityStatus

impl Debug for ChassisState

impl Debug for ChassisType

impl Debug for CoolingDeviceStatus

impl Debug for CoolingDeviceType

impl Debug for CoreCount2

impl Debug for CoreCount

impl Debug for CoresEnabled2

impl Debug for CoresEnabled

impl Debug for CpuStatus

impl Debug for CurrentProbeAccuracy

impl Debug for CurrentProbeLocation

impl Debug for CurrentProbeResolution

impl Debug for CurrentProbeStatus

impl Debug for DeviceFunctionNumber

impl Debug for DeviceStatus

impl Debug for ElementMaximum

impl Debug for ElementMinimum

impl Debug for ElementType

impl Debug for ErrorCorrectionType

impl Debug for ErrorDetectingMethod

impl Debug for FirmwareIdFormat

impl Debug for FirmwareImageSize

impl Debug for FirmwareInventoryStateInformation

impl Debug for HardwareSecurityStatus

impl Debug for HeaderFormat

impl Debug for HostInterfaceType

impl Debug for HostProtocolType

impl Debug for InputVoltageRangeSwitching

impl Debug for InterleaveSupport

impl Debug for InterruptInfo

impl Debug for InterruptPolarity

impl Debug for InterruptTriggerMode

impl Debug for IpmiInterfaceType

impl Debug for LanguageFormat

impl Debug for LogType

impl Debug for M2SlotType

impl Debug for MXMSlotType

impl Debug for ManagementDeviceAddressType

impl Debug for ManagementDeviceType

impl Debug for MaxPowerCapacity

impl Debug for MaximumMemoryCapacity

impl Debug for MemoryArrayErrorCorrection

impl Debug for MemoryArrayLocation

impl Debug for MemoryArrayUse

impl Debug for MemoryChannelType

impl Debug for MemoryDeviceTechnology

impl Debug for MemoryDeviceType

impl Debug for MemoryErrorGranularity

impl Debug for MemoryErrorOperation

impl Debug for MemoryErrorType

impl Debug for MemoryFormFactor

impl Debug for MemoryIndicatedSize

impl Debug for MemorySize

impl Debug for MemorySizeExtended

impl Debug for MemorySpeed

impl Debug for MemorySpeedExtended

impl Debug for PciExpressGeneration

impl Debug for PciExpressSlotWidth

Trait Debug