Trait Debug

1.0.0 · Source

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

Expand description

Re-export Debug, to avoid dependency clutter. ? 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 subsoil::allocator::Error

impl Debug for ApiError

impl Debug for ArithmeticError

impl Debug for Rounding

impl Debug for SignedRounding

impl Debug for CheckInherentsError

impl Debug for NextConfigDescriptor

impl Debug for PreDigest

impl Debug for AllowedSlots

impl Debug for SignatureResult

impl Debug for subsoil::core::crypto::AddressUriError

impl Debug for DeriveError

impl Debug for DeriveJunction

impl Debug for PublicError

impl Debug for SecretStringError

impl Debug for Ss58AddressFormatRegistry

impl Debug for Void

impl Debug for HttpError

impl Debug for HttpRequestStatus

impl Debug for OffchainOverlayedChange

impl Debug for StorageKind

impl Debug for CallContext

impl Debug for subsoil::externalities::Error

impl Debug for TransactionType

impl Debug for subsoil::inherents::Error

impl Debug for subsoil::keyring::ed25519::Keyring

impl Debug for subsoil::keyring::sr25519::Keyring

impl Debug for subsoil::keystore::Error

impl Debug for StorageEntryModifierIR

impl Debug for StorageHasherIR

impl Debug for subsoil::mmr::Error

impl Debug for subsoil::npos_elections::Error

impl Debug for OffenceError

impl Debug for BackendTrustLevel

impl Debug for ExecutionError

impl Debug for IndexOperation

impl Debug for subsoil::std::cmp::Ordering

impl Debug for Infallible

impl Debug for subsoil::std::fmt::Alignment

impl Debug for DebugAsHex

impl Debug for Sign

impl Debug for Abi

impl Debug for Generic

impl Debug for TypeKind

impl Debug for FpCategory

impl Debug for IntErrorKind

impl Debug for subsoil::std::slice::GetDisjointMutError

impl Debug for SearchStep

impl Debug for subsoil::std::sync::atomic::Ordering

impl Debug for subsoil::std::sync::mpmc::RecvTimeoutError

impl Debug for subsoil::std::sync::mpmc::TryRecvError

impl Debug for ChildInfo

impl Debug for ChildType

impl Debug for StateVersion

impl Debug for InherentError

impl Debug for WasmLevel

impl Debug for WasmValue

impl Debug for TraceBlockResponse

impl Debug for subsoil::trie::accessed_nodes_tracker::Error

impl Debug for NodePlan

impl Debug for StorageProofError

impl Debug for ValuePlan

impl Debug for subsoil::version::embed::Error

impl Debug for ReturnValue

impl Debug for subsoil::wasm_interface::Value

impl Debug for subsoil::wasm_interface::ValueType

impl Debug for subsoil::runtime::DispatchError

impl Debug for ExtrinsicInclusionMode

impl Debug for MultiSignature

impl Debug for MultiSigner

impl Debug for TokenError

Trait Debug