Trait charts::prelude::fmt::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

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,
)");

Implementors

source

impl Debug for _Unwind_Reason_Code

The Debug output of the ISO week w is the same as d.format("%G-W%V") where d is any NaiveDate value in that week.

Example

use chrono::{NaiveDate, Datelike};

assert_eq!(format!("{:?}", NaiveDate::from_ymd(2015,  9,  5).iso_week()), "2015-W36");
assert_eq!(format!("{:?}", NaiveDate::from_ymd(   0,  1,  3).iso_week()), "0000-W01");
assert_eq!(format!("{:?}", NaiveDate::from_ymd(9999, 12, 31).iso_week()), "9999-W52");

ISO 8601 requires an explicit sign for years before 1 BCE or after 9999 CE.

assert_eq!(format!("{:?}", NaiveDate::from_ymd(    0,  1,  2).iso_week()),  "-0001-W52");
assert_eq!(format!("{:?}", NaiveDate::from_ymd(10000, 12, 31).iso_week()), "+10000-W52");

The Debug output of the naive date d is the same as d.format("%Y-%m-%d").

The string printed can be readily parsed via the parse method on str.

Example

use chrono::NaiveDate;

assert_eq!(format!("{:?}", NaiveDate::from_ymd(2015,  9,  5)), "2015-09-05");
assert_eq!(format!("{:?}", NaiveDate::from_ymd(   0,  1,  1)), "0000-01-01");
assert_eq!(format!("{:?}", NaiveDate::from_ymd(9999, 12, 31)), "9999-12-31");

ISO 8601 requires an explicit sign for years before 1 BCE or after 9999 CE.

assert_eq!(format!("{:?}", NaiveDate::from_ymd(   -1,  1,  1)),  "-0001-01-01");
assert_eq!(format!("{:?}", NaiveDate::from_ymd(10000, 12, 31)), "+10000-12-31");

The Debug output of the naive date and time dt is the same as dt.format("%Y-%m-%dT%H:%M:%S%.f").

The string printed can be readily parsed via the parse method on str.

It should be noted that, for leap seconds not on the minute boundary, it may print a representation not distinguishable from non-leap seconds. This doesn’t matter in practice, since such leap seconds never happened. (By the time of the first leap second on 1972-06-30, every time zone offset around the world has standardized to the 5-minute alignment.)

Example

use chrono::NaiveDate;

let dt = NaiveDate::from_ymd(2016, 11, 15).and_hms(7, 39, 24);
assert_eq!(format!("{:?}", dt), "2016-11-15T07:39:24");

Leap seconds may also be used.

let dt = NaiveDate::from_ymd(2015, 6, 30).and_hms_milli(23, 59, 59, 1_500);
assert_eq!(format!("{:?}", dt), "2015-06-30T23:59:60.500");

The Debug output of the naive time t is the same as t.format("%H:%M:%S%.f").

The string printed can be readily parsed via the parse method on str.

It should be noted that, for leap seconds not on the minute boundary, it may print a representation not distinguishable from non-leap seconds. This doesn’t matter in practice, since such leap seconds never happened. (By the time of the first leap second on 1972-06-30, every time zone offset around the world has standardized to the 5-minute alignment.)

Example

use chrono::NaiveTime;

assert_eq!(format!("{:?}", NaiveTime::from_hms(23, 56, 4)),              "23:56:04");
assert_eq!(format!("{:?}", NaiveTime::from_hms_milli(23, 56, 4, 12)),    "23:56:04.012");
assert_eq!(format!("{:?}", NaiveTime::from_hms_micro(23, 56, 4, 1234)),  "23:56:04.001234");
assert_eq!(format!("{:?}", NaiveTime::from_hms_nano(23, 56, 4, 123456)), "23:56:04.000123456");

Leap seconds may also be used.

assert_eq!(format!("{:?}", NaiveTime::from_hms_milli(6, 59, 59, 1_500)), "06:59:60.500");
1.27.0 · source

impl Debug for __m128

source

impl Debug for __m128bh

1.27.0 · source

impl Debug for __m128d

1.27.0 · source

impl Debug for __m128i

1.27.0 · source

impl Debug for __m256

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impl Debug for __m256bh

1.27.0 · source

impl Debug for __m256d

1.27.0 · source

impl Debug for __m256i

source

impl Debug for __m512

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impl Debug for __m512bh

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impl Debug for __m512d

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impl Debug for __m512i

source

impl Debug for Text

impl Debug for FT_BBox_

impl Debug for FT_Bitmap_

impl Debug for FT_Bitmap_Size_

impl Debug for FT_CharMapRec_

impl Debug for FT_Data_

impl Debug for FT_DriverRec_

impl Debug for FT_Encoding_

impl Debug for FT_FaceRec_

impl Debug for FT_Face_InternalRec_

impl Debug for FT_Generic_

impl Debug for FT_GlyphSlotRec_

impl Debug for FT_Glyph_Format_

impl Debug for FT_Glyph_Metrics_

impl Debug for FT_Kerning_Mode_

impl Debug for FT_LcdFilter_

impl Debug for FT_LibraryRec_

impl Debug for FT_ListNodeRec_

impl Debug for FT_ListRec_

impl Debug for FT_Matrix_

impl Debug for FT_MemoryRec_

impl Debug for FT_ModuleRec_

impl Debug for FT_Module_Class_

impl Debug for FT_Open_Args_

impl Debug for FT_Orientation_

impl Debug for FT_Outline_

impl Debug for FT_Outline_Funcs_

impl Debug for FT_Parameter_

impl Debug for FT_Pixel_Mode_

impl Debug for FT_RasterRec_

impl Debug for FT_Raster_Funcs_

impl Debug for FT_Raster_Params_

impl Debug for FT_Render_Mode_

impl Debug for FT_RendererRec_

impl Debug for FT_Sfnt_Tag_

impl Debug for FT_SizeRec_

impl Debug for FT_Size_InternalRec_

impl Debug for FT_Size_Metrics_

impl Debug for FT_Size_RequestRec_

impl Debug for FT_Size_Request_Type_

impl Debug for FT_Slot_InternalRec_

impl Debug for FT_Span_

impl Debug for FT_StreamDesc_

impl Debug for FT_StreamRec_

impl Debug for FT_SubGlyphRec_

impl Debug for FT_TrueTypeEngineType_

impl Debug for FT_UnitVector_

impl Debug for FT_Vector_

impl Debug for _bindgen_ty_1

impl Debug for _bindgen_ty_2

This trait is implemented for function pointers with up to twelve arguments.

This trait is implemented for function pointers with up to twelve arguments.

This trait is implemented for function pointers with up to twelve arguments.

This trait is implemented for function pointers with up to twelve arguments.

This trait is implemented for function pointers with up to twelve arguments.

This trait is implemented for function pointers with up to twelve arguments.

This trait is implemented for tuples up to twelve items long.

impl<T> Debug for __BindgenUnionField<T>