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 BackupError

impl Debug for AclMode

impl Debug for ArrayBuilderImpl

impl Debug for ArrayImpl

impl Debug for ArrayError

impl Debug for risingwave_common::array::stream_chunk::Op

impl Debug for risingwave_common::array::stream_record::RecordType

impl Debug for StructRef<'_>

impl Debug for SystemColumn

impl Debug for ConflictBehavior

impl Debug for risingwave_common::catalog::CreateType

impl Debug for risingwave_common::catalog::StreamJobStatus

impl Debug for AsyncStackTraceOption

impl Debug for CacheEvictionConfig

impl Debug for CompactorMode

impl Debug for DefaultParallelism

impl Debug for risingwave_common::config::EvictionConfig

impl Debug for risingwave_common::config::MetaBackend

impl Debug for VnodeCount

impl Debug for SessionConfigError

impl Debug for risingwave_common::session_config::over_window::OverWindowCachePolicy

impl Debug for QueryMode

impl Debug for SinkDecouple

impl Debug for VisibilityMode

impl Debug for risingwave_common::telemetry::TelemetryNodeType

impl Debug for TxnMsg

impl Debug for risingwave_common::types::decimal::Decimal

impl Debug for DataTypeName

impl Debug for risingwave_common::types::interval::DateTimeField

impl Debug for Deployment

impl Debug for MetaAddressStrategy

impl Debug for MetaAddressStrategyParseError

impl Debug for risingwave_common::util::sort_util::Direction

impl Debug for ValueEncodingError

impl Debug for MetricLevel

impl Debug for SecretError

impl Debug for ObserverError

impl Debug for QualityOfService

impl Debug for AccessBuilderImpl

impl Debug for ByteStreamSourceParserImpl

impl Debug for EncodingProperties

impl Debug for risingwave_connector::parser::EncodingType

impl Debug for risingwave_connector::parser::ParseResult

impl Debug for ParserFormat

impl Debug for ProtocolProperties

impl Debug for SchemaLocation

impl Debug for TransactionControl

impl Debug for TimestamptzHandling

impl Debug for SchemaFetchError

impl Debug for SinkEncode

impl Debug for SinkFormat

impl Debug for risingwave_connector::sink::catalog::SinkType

impl Debug for AvroHeader

impl Debug for ProtoHeader

impl Debug for SinkError

impl Debug for SinkImpl

impl Debug for EngineType

impl Debug for PathPartitionPrefix

impl Debug for risingwave_connector::sink::kafka::CompressionCodec

impl Debug for LogStoreReadItem

impl Debug for TruncateOffset

impl Debug for BackfillInfo

impl Debug for ConnectorProperties

impl Debug for SourceEncode

impl Debug for risingwave_connector::source::base::SourceFormat

impl Debug for SourceMeta

impl Debug for SplitImpl

impl Debug for CdcOffset

impl Debug for CdcTableType

impl Debug for risingwave_connector::source::cdc::external::SslMode

impl Debug for risingwave_connector::source::cdc::source::message::CdcMessageType

impl Debug for risingwave_connector::source::filesystem::file_common::CompressionFormat

Trait Debug