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 TryReserveErrorKind

impl Debug for solar::ast::bumpalo::core_alloc::slice::GetDisjointMutError

impl Debug for SearchStep

impl Debug for Base

impl Debug for BinOpKind

impl Debug for CommentKind

impl Debug for ContractKind

impl Debug for DataLocation

impl Debug for ElementaryType

impl Debug for EtherSubDenomination

impl Debug for FunctionKind

impl Debug for IdentOrStrLit

impl Debug for ItemKind<'_>

impl Debug for LitKind<'_>

impl Debug for Op

impl Debug for SemverReqComponentKind

impl Debug for SemverVersionNumber

impl Debug for solar::ast::StateMutability

impl Debug for StrKind

impl Debug for SubDenomination

impl Debug for TimeSubDenomination

impl Debug for solar::ast::TypeKind<'_>

impl Debug for UnOpKind

impl Debug for UserDefinableOperator

impl Debug for VarMut

impl Debug for Visibility

impl Debug for BinOpToken

impl Debug for Delimiter

impl Debug for TokenDescription

impl Debug for TokenKind

impl Debug for TokenLitKind

impl Debug for solar::config::ColorChoice

impl Debug for CompilerOutput

impl Debug for CompilerStage

impl Debug for DumpKind

impl Debug for ErrorFormat

impl Debug for EvmVersion

impl Debug for HumanEmitterKind

impl Debug for Language

impl Debug for Applicability

impl Debug for solar::interface::diagnostics::Level

impl Debug for solar::interface::diagnostics::Style

impl Debug for SuggestionStyle

impl Debug for Suggestions

impl Debug for FileName

impl Debug for ResolveError

impl Debug for SpanLinesError

impl Debug for SpanSnippetError

impl Debug for Recovered

impl Debug for RawLiteralKind

impl Debug for RawTokenKind

impl Debug for EscapeError

impl Debug for Builtin

impl Debug for EvalErrorKind

impl Debug for solar::sema::hir::ItemId

impl Debug for LoopSource

impl Debug for Res

impl Debug for VarKind

impl Debug for Recursiveness

impl Debug for TyAbiPrinterMode

impl Debug for CollectionAllocErr

impl Debug for solar::data_structures::fmt::Alignment

impl Debug for DebugAsHex

impl Debug for solar::data_structures::fmt::Sign

impl Debug for AsciiChar

impl Debug for core::cmp::Ordering

impl Debug for Infallible

impl Debug for FromBytesWithNulError

impl Debug for c_void

impl Debug for AtomicOrdering

impl Debug for IpAddr

Trait Debug