Trait usenetnews_dynexp2::prelude::Debug

1.0.0 · source ·

pub trait Debug {
    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 (libstd, libcore, liballoc, 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 };

assert_eq!(format!("The origin is: {origin:#?}"),
"The origin is: Point {
    x: 0,
    y: 0,
}");

Required Methods§

source

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

Formats the value using the given formatter.

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 usenetnews_dynexp2::prelude::Debug

Stability

Examples

Required Methods§

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

Examples

Implementors§

impl Debug for usenetnews_dynexp2::prelude::Ordering

impl Debug for VarError

impl Debug for usenetnews_dynexp2::prelude::fmt::Alignment

impl Debug for TryReserveErrorKind

impl Debug for Infallible

impl Debug for Which

impl Debug for c_void

impl Debug for FpCategory

impl Debug for IntErrorKind

impl Debug for SearchStep

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

impl Debug for BacktraceStatus

impl Debug for std::net::Shutdown

impl Debug for std::net::ip_addr::IpAddr

impl Debug for Ipv6MulticastScope

impl Debug for std::net::socket_addr::SocketAddr

impl Debug for AncillaryError

impl Debug for BacktraceStyle

impl Debug for RecvTimeoutError

impl Debug for TryRecvError

impl Debug for _Unwind_Reason_Code

impl Debug for ArgAction

impl Debug for AppSettings

impl Debug for ArgSettings

impl Debug for ValueHint

impl Debug for ContextKind

impl Debug for ContextValue

impl Debug for clap::error::kind::ErrorKind

impl Debug for MatchesError

impl Debug for ValueSource

impl Debug for clap::util::color::ColorChoice

impl Debug for humantime::date::Error

impl Debug for humantime::duration::Error

impl Debug for Type

impl Debug for Errno

impl Debug for FlockArg

impl Debug for PosixFadviseAdvice

impl Debug for AioCancelStat

impl Debug for AioFsyncMode

impl Debug for LioMode

impl Debug for EpollOp

impl Debug for MmapAdvise

impl Debug for Event

impl Debug for Request

impl Debug for QuotaFmt

impl Debug for QuotaType

impl Debug for RebootMode

impl Debug for Resource

impl Debug for UsageWho

impl Debug for SigHandler

impl Debug for SigevNotify

impl Debug for SigmaskHow

impl Debug for Signal

impl Debug for AddressFamily

impl Debug for InetAddr

impl Debug for nix::sys::socket::addr::IpAddr

impl Debug for SockAddr

impl Debug for ControlMessageOwned

impl Debug for nix::sys::socket::Shutdown

impl Debug for SockProtocol

impl Debug for nix::sys::socket::SockType

impl Debug for FchmodatFlags

impl Debug for UtimensatFlags

impl Debug for BaudRate

impl Debug for FlowArg

impl Debug for FlushArg

impl Debug for SetArg

impl Debug for SpecialCharacterIndices

impl Debug for Expiration

impl Debug for nix::sys::timerfd::ClockId

impl Debug for Id

impl Debug for WaitStatus

impl Debug for FchownatFlags