Trait frame_support::dispatch::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 };

assert_eq!(format!("The origin is: {origin:#?}"),
"The origin is: Point {
    x: 0,
    y: 0,
}");

Required Methods§

source

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

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,
)");

Trait frame_support::dispatch::fmt::Debug

Stability

Examples

Required Methods§

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

Examples

Implementors§

impl Debug for &dyn TargetIsa

impl Debug for ApiError

impl Debug for ArithmeticError

impl Debug for Rounding

impl Debug for SignedRounding

impl Debug for DeriveError

impl Debug for DeriveJunction

impl Debug for PublicError

impl Debug for SecretStringError

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 sp_externalities::Error

impl Debug for sp_inherents::Error

impl Debug for sp_keystore::Error

impl Debug for StorageEntryModifierIR

impl Debug for StorageHasherIR

impl Debug for MultiSignature

impl Debug for MultiSigner

impl Debug for TokenError

impl Debug for TransactionalError

impl Debug for DigestItem

impl Debug for Era

impl Debug for sp_runtime::legacy::byte_sized_error::DispatchError

impl Debug for sp_runtime::offchain::http::Error

impl Debug for Method

impl Debug for StorageRetrievalError

impl Debug for RuntimeString

impl Debug for DisableStrategy

impl Debug for OffenceError

impl Debug for ExecutionError

impl Debug for BackendTrustLevel

impl Debug for IndexOperation

impl Debug for WasmLevel

impl Debug for WasmValue

impl Debug for sp_version::embed::Error

impl Debug for ReturnValue

impl Debug for sp_wasm_interface::Value

impl Debug for sp_wasm_interface::ValueType

impl Debug for Never

impl Debug for frame_support::pallet_prelude::DispatchError

impl Debug for InvalidTransaction

impl Debug for TransactionSource

impl Debug for TransactionValidityError

impl Debug for UnknownTransaction

impl Debug for ChildInfo

impl Debug for ChildType

impl Debug for StateVersion

impl Debug for ExecuteOverweightError

impl Debug for ProcessMessageError

impl Debug for frame_support::traits::TryStateSelect

impl Debug for UpgradeCheckSelect

impl Debug for frame_support::traits::schedule::LookupError

impl Debug for BalanceStatus

impl Debug for DepositConsequence

impl Debug for ExistenceRequirement

impl Debug for Fortitude

impl Debug for Precision

impl Debug for Preservation

impl Debug for Provenance

impl Debug for Restriction

impl Debug for PaymentStatus

impl Debug for DispatchClass

impl Debug for Pays

impl Debug for frame_support::dispatch::fmt::Alignment

impl Debug for TryReserveErrorKind

impl Debug for core::cmp::Ordering

impl Debug for Infallible

impl Debug for Which

impl Debug for c_void