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,
)");

Debug

Trait Debug Copy item path

§Stability

§Examples

Required Methods§

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

§Errors

§Examples

Implementors§

impl Debug for AnsiColorKind

impl Debug for AnsiColorLayer

impl Debug for AppError

impl Debug for AppEvent

impl Debug for AppMessage

impl Debug for FlowMessage

impl Debug for AssetLifetime

impl Debug for AnyFormat

impl Debug for FormatMarkup

impl Debug for FormatSpecial

impl Debug for hexga_engine::graphics::gpu::Backend

impl Debug for BufferUsage

impl Debug for hexga_engine::graphics::gpu::PowerPreference

impl Debug for AddressMode

impl Debug for AstcBlock

impl Debug for AstcChannel

impl Debug for hexga_engine::graphics::gpu::wgpu::Backend

impl Debug for BindingType

impl Debug for hexga_engine::graphics::gpu::wgpu::BlendFactor

impl Debug for BlendOperation

impl Debug for BufferBindingType

impl Debug for CompareFunction

impl Debug for CompilationMessageType

impl Debug for CompositeAlphaMode

impl Debug for DeviceLostReason

impl Debug for hexga_engine::graphics::gpu::wgpu::DeviceType

impl Debug for Dx12Compiler

impl Debug for DxcShaderModel

impl Debug for hexga_engine::graphics::gpu::wgpu::Error

impl Debug for ErrorFilter

impl Debug for hexga_engine::graphics::gpu::wgpu::Face

impl Debug for FilterMode

impl Debug for hexga_engine::graphics::gpu::wgpu::FrontFace

impl Debug for GlFenceBehavior

impl Debug for Gles3MinorVersion

impl Debug for IndexFormat

impl Debug for MapMode

impl Debug for MemoryHints

impl Debug for PollError

impl Debug for PollStatus

impl Debug for hexga_engine::graphics::gpu::wgpu::PolygonMode

impl Debug for hexga_engine::graphics::gpu::wgpu::PowerPreference

impl Debug for PredefinedColorSpace

impl Debug for hexga_engine::graphics::gpu::wgpu::PresentMode

impl Debug for hexga_engine::graphics::gpu::wgpu::PrimitiveTopology

impl Debug for hexga_engine::graphics::gpu::wgpu::QueryType

impl Debug for RequestAdapterError

impl Debug for SamplerBindingType

impl Debug for SamplerBorderColor

impl Debug for hexga_engine::graphics::gpu::wgpu::ShaderModel

impl Debug for StencilOperation

impl Debug for StorageTextureAccess

impl Debug for StoreOp

impl Debug for hexga_engine::graphics::gpu::wgpu::SurfaceError

impl Debug for SurfaceStatus

impl Debug for TextureAspect

impl Debug for TextureDimension

impl Debug for TextureFormat

impl Debug for TextureSampleType

impl Debug for TextureViewDimension

impl Debug for Trace

impl Debug for VertexFormat

impl Debug for VertexStepMode

impl Debug for AccelerationStructureBuildMode

impl Debug for AccelerationStructureFormat

impl Debug for hexga_engine::graphics::gpu::wgpu::hal::DeviceError

impl Debug for PipelineCacheError

impl Debug for PipelineError

impl Debug for hexga_engine::graphics::gpu::wgpu::hal::ShaderError

impl Debug for hexga_engine::graphics::gpu::wgpu::hal::SurfaceError

impl Debug for TextureInner

Trait Debug