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,
)");

Trait DebugCopy item path

§Stability

§Examples

Required Methods§

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

§Errors

§Examples

Implementors§

impl Debug for Reason

impl Debug for ExperimentalTarget

impl Debug for NetTarget

impl Debug for ParseExperimentalTargetError

impl Debug for ParseFuncTargetError

impl Debug for RouteTarget

impl Debug for surrealdb_core::dbs::Action

impl Debug for Force

impl Debug for Futures

impl Debug for QueryType

impl Debug for surrealdb_core::dbs::Status

impl Debug for surrealdb_core::err::Error

impl Debug for surrealdb_core::iam::entities::Action

impl Debug for ConfigKind

impl Debug for surrealdb_core::iam::entities::Level

impl Debug for ResourceKind

impl Debug for Role

impl Debug for surrealdb_core::iam::Error

impl Debug for Audience

impl Debug for MTreeNode

impl Debug for SerializedVector

impl Debug for Vector

impl Debug for Check

impl Debug for TableConfig

impl Debug for surrealdb_core::rpc::Data

impl Debug for RpcError

impl Debug for surrealdb_core::rpc::format::Format

impl Debug for surrealdb_core::rpc::method::Method

impl Debug for AccessType

impl Debug for surrealdb_core::sql::Algorithm

impl Debug for surrealdb_core::sql::Base

impl Debug for Constant

impl Debug for surrealdb_core::sql::Data

impl Debug for surrealdb_core::sql::Dir

impl Debug for surrealdb_core::sql::Entry

impl Debug for surrealdb_core::sql::Expression

impl Debug for surrealdb_core::sql::Field

impl Debug for surrealdb_core::sql::Filter

impl Debug for surrealdb_core::sql::Function

impl Debug for surrealdb_core::sql::Geometry

impl Debug for surrealdb_core::sql::Id

impl Debug for surrealdb_core::sql::Kind

impl Debug for surrealdb_core::sql::Literal

impl Debug for Mock

impl Debug for surrealdb_core::sql::Number

impl Debug for Operation

impl Debug for surrealdb_core::sql::Operator

impl Debug for surrealdb_core::sql::Output

impl Debug for surrealdb_core::sql::Part

impl Debug for Permission

impl Debug for Scoring

impl Debug for Statement

impl Debug for Subquery

impl Debug for TableType

impl Debug for Tokenizer

impl Debug for surrealdb_core::sql::Value

impl Debug for surrealdb_core::sql::With

impl Debug for Distance1

impl Debug for Distance

impl Debug for Index

impl Debug for VectorType

impl Debug for AccessStatement

impl Debug for AlterStatement

impl Debug for AnalyzeStatement

impl Debug for DefineStatement

impl Debug for InfoStatement

impl Debug for RemoveStatement

impl Debug for MessageKind

impl Debug for NumberKind

impl Debug for NumericKind

impl Debug for CharError

impl Debug for Delim

Trait Debug