Trait Debug

1.6.0 · 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,
)");

Debug

Trait Debug Copy item path

§Stability

§Examples

Required Methods§

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

§Errors

§Examples

Implementors§

impl Debug for AsciiChar

impl Debug for mmcp_server::inventory::core::cmp::Ordering

impl Debug for Infallible

impl Debug for FromBytesWithNulError

impl Debug for c_void

impl Debug for AtomicOrdering

impl Debug for IpAddr

impl Debug for Ipv6MulticastScope

impl Debug for mmcp_server::inventory::core::net::SocketAddr

impl Debug for FpCategory

impl Debug for IntErrorKind

impl Debug for mmcp_server::inventory::core::slice::GetDisjointMutError

impl Debug for SearchStep

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

impl Debug for mmcp_server::inventory::core::fmt::Alignment

impl Debug for DebugAsHex

impl Debug for Sign

impl Debug for TryReserveErrorKind

impl Debug for BacktraceStatus

impl Debug for VarError

impl Debug for std::fs::TryLockError

impl Debug for SeekFrom

impl Debug for ErrorKind

impl Debug for Shutdown

impl Debug for AncillaryError

impl Debug for BacktraceStyle

impl Debug for RecvTimeoutError

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

impl Debug for ParseAlphabetError

impl Debug for DecodeError

impl Debug for DecodeSliceError

impl Debug for EncodeSliceError

impl Debug for DecodePaddingMode

impl Debug for PollNext

impl Debug for hashbrown::TryReserveError

impl Debug for indexmap::GetDisjointMutError

impl Debug for PrefilterConfig

impl Debug for ProtocolVersion

impl Debug for CallToolResultContent

impl Debug for ClientNotification

impl Debug for ClientRequest

impl Debug for ClientResult

impl Debug for CompleteRequestParamsRef

impl Debug for CreateMessageRequestParamsIncludeContext

impl Debug for CreateMessageResultContent

impl Debug for EmbeddedResourceResource

impl Debug for JSONRPCMessage

impl Debug for JsonrpcBatchRequestItem

impl Debug for JsonrpcBatchResponseItem

impl Debug for LoggingLevel

impl Debug for ProgressToken

impl Debug for PromptMessageContent

impl Debug for ReadResourceResultContents

impl Debug for RequestId

impl Debug for Role

impl Debug for SamplingMessageContent

impl Debug for ServerNotification

impl Debug for ServerRequest

impl Debug for ServerResult

impl Debug for RPCPortError

impl Debug for Category

impl Debug for Value

impl Debug for slab::GetDisjointMutError

impl Debug for bool

impl Debug for char

impl Debug for f16

impl Debug for f32

impl Debug for f64

impl Debug for f128

impl Debug for i8

impl Debug for i16

Trait Debug