Trait wasmtime_environ::__core::fmt::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,
)");

Trait wasmtime_environ::__core::fmt::DebugCopy item path

§Stability

§Examples

Required Methods§

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

§Errors

§Examples

Implementors§

impl Debug for hashbrown::TryReserveError

impl Debug for log::Level

impl Debug for LevelFilter

impl Debug for PrefilterConfig

impl Debug for CDataModel

impl Debug for Size

impl Debug for target_lexicon::parse_error::ParseError

impl Debug for Aarch64Architecture

impl Debug for target_lexicon::targets::Architecture

impl Debug for ArmArchitecture

impl Debug for target_lexicon::targets::BinaryFormat

impl Debug for CustomVendor

impl Debug for Environment

impl Debug for Mips32Architecture

impl Debug for Mips64Architecture

impl Debug for OperatingSystem

impl Debug for Riscv32Architecture

impl Debug for Riscv64Architecture

impl Debug for Vendor

impl Debug for X86_32Architecture

impl Debug for CallingConvention

impl Debug for target_lexicon::triple::Endianness

impl Debug for PointerWidth

impl Debug for BidiClass

impl Debug for Direction

impl Debug for unicode_bidi::level::Error

impl Debug for IsNormalized

impl Debug for Origin

impl Debug for url::parser::ParseError

impl Debug for SyntaxViolation

impl Debug for Position

impl Debug for CompileError

impl Debug for EntityIndex

impl Debug for wasmtime_environ::EntityType

impl Debug for FlagValue

impl Debug for GlobalInit

impl Debug for Initializer

impl Debug for MemoryInitialization

impl Debug for MemoryStyle

impl Debug for wasmtime_environ::ModuleType

impl Debug for SettingKind

impl Debug for TableInitialization

impl Debug for TableStyle

impl Debug for Trap

impl Debug for WasmError

impl Debug for WasmType

impl Debug for BlockType

impl Debug for CanonicalFunction

impl Debug for CanonicalOption

impl Debug for ComponentExternalKind

impl Debug for ComponentOuterAliasKind

impl Debug for ComponentTypeRef

impl Debug for wasmtime_environ::wasmparser::ComponentValType

impl Debug for wasmtime_environ::wasmparser::Encoding

impl Debug for ExternalKind

impl Debug for FrameKind

impl Debug for HeapType

impl Debug for InstantiationArgKind

impl Debug for OuterAliasKind

impl Debug for Payload<'_>

impl Debug for PrimitiveValType

impl Debug for TagKind

impl Debug for wasmtime_environ::wasmparser::Type

impl Debug for TypeBounds

impl Debug for TypeRef

impl Debug for ValType

impl Debug for wasmtime_environ::wasmparser::types::ComponentDefinedType

impl Debug for ComponentEntityType

impl Debug for ComponentInstanceTypeKind

impl Debug for wasmtime_environ::wasmparser::types::ComponentValType

impl Debug for wasmtime_environ::wasmparser::types::EntityType

impl Debug for InstanceTypeKind

Trait wasmtime_environ::__core::fmt::Debug