Trait Debug

Help

1.0.0 · Source

pub trait Debug {
    // Required method
    fn fmt(&self, f: &mut Formatter<'_>) -> Result<(), Error> ⓘ;
}

Expand description

core ? formatting.

Re-exported from core::fmt:: .

? 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);

impl Debug for UnitSi

Available on crate feature unit only.

Source §

impl Debug for devela::text::AsciiChar

Source §

impl Debug for InvalidText

Source §

impl Debug for TextError

Available on crate feature draw only.

Source §

impl Debug for EncodingMode

1.28.0 · Source§

impl Debug for devela::all::FmtAlignment

Source §

impl Debug for devela::all::FontError

Available on crate feature font only.

Source §

impl Debug for devela::all::ImageError

Available on crate feature image only.

1.0.0 · Source§

impl Debug for ErrorKind

1.7.0 · Source§

impl Debug for IpAddr

Source §

impl Debug for JsEvent

Available on crate feature js only.

Source §

impl Debug for JsPermission

Available on crate feature js only.

Source §

impl Debug for JsPermissionState

Available on crate feature js only.

Source §

impl Debug for devela::all::LayoutError

Available on crate feature layout only.

Source §

impl Debug for devela::all::LogLevel

Source §

impl Debug for devela::all::LogLevelFilter

Source §

impl Debug for MediaError

Available on media·· only.

Source §

impl Debug for MidiError

Available on crate feature midi only.

impl Debug for SixelError

Available on crate feature alloc and crate feature term and (crate features io or std) and (crate features dep_hashbrown or std) and crate feature image only.

Source §

impl Debug for SixelMean

Available on crate feature alloc and crate feature term and (crate features io or std) and (crate features dep_hashbrown or std) and crate feature image only.

Source §

impl Debug for SixelQuality

Available on crate feature alloc and crate feature term and (crate features io or std) and (crate features dep_hashbrown or std) and crate feature image only.

Source §

impl Debug for SixelSplit

Available on crate feature alloc and crate feature term and (crate features io or std) and (crate features dep_hashbrown or std) and crate feature image only.

1.0.0 · Source§

impl Debug for devela::all::SocketAddr

Source §

Converts a DateTime into a human readable datetime string.

(This Debug representation currently emits the same string as the Display representation, but this is not a guarantee.)

Options currently supported:

std::fmt::Formatter::precision can be set to control the precision of the fractional second component.

§Example

use jiff::civil::date;

let dt = date(2024, 6, 15).at(7, 0, 0, 123_000_000);
assert_eq!(format!("{dt:.6?}"), "2024-06-15T07:00:00.123000");
// Precision values greater than 9 are clamped to 9.
assert_eq!(format!("{dt:.300?}"), "2024-06-15T07:00:00.123000000");
// A precision of 0 implies the entire fractional
// component is always truncated.
assert_eq!(format!("{dt:.0?}"), "2024-06-15T07:00:00");

Converts a Time into a human readable time string.

(This Debug representation currently emits the same string as the Display representation, but this is not a guarantee.)

Options currently supported:

std::fmt::Formatter::precision can be set to control the precision of the fractional second component.

§Example

use jiff::civil::time;

let t = time(7, 0, 0, 123_000_000);
assert_eq!(format!("{t:.6?}"), "07:00:00.123000");
// Precision values greater than 9 are clamped to 9.
assert_eq!(format!("{t:.300?}"), "07:00:00.123000000");
// A precision of 0 implies the entire fractional
// component is always truncated.
assert_eq!(format!("{t:.0?}"), "07:00:00");

Options currently supported:

std::fmt::Formatter::precision can be set to control the precision of the fractional second component.

§Example

use jiff::Timestamp;

let ts = Timestamp::new(1_123_456_789, 123_000_000)?;
assert_eq!(
    format!("{ts:.6?}"),
    "2005-08-07T23:19:49.123000Z",
);
// Precision values greater than 9 are clamped to 9.
assert_eq!(
    format!("{ts:.300?}"),
    "2005-08-07T23:19:49.123000000Z",
);
// A precision of 0 implies the entire fractional
// component is always truncated.
assert_eq!(
    format!("{ts:.0?}"),
    "2005-08-07T23:19:49Z",
);

Converts a Zoned datetime into a human readable datetime string.

(This Debug representation currently emits the same string as the Display representation, but this is not a guarantee.)

Options currently supported:

std::fmt::Formatter::precision can be set to control the precision of the fractional second component.

§Example

use jiff::civil::date;

let zdt = date(2024, 6, 15).at(7, 0, 0, 123_000_000).in_tz("US/Eastern")?;
assert_eq!(
    format!("{zdt:.6?}"),
    "2024-06-15T07:00:00.123000-04:00[US/Eastern]",
);
// Precision values greater than 9 are clamped to 9.
assert_eq!(
    format!("{zdt:.300?}"),
    "2024-06-15T07:00:00.123000000-04:00[US/Eastern]",
);
// A precision of 0 implies the entire fractional
// component is always truncated.
assert_eq!(
    format!("{zdt:.0?}"),
    "2024-06-15T07:00:00-04:00[US/Eastern]",
);