vrl::compiler::prelude::fmt

Trait Display

1.0.0 · Source

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

Expand description

Format trait for an empty format, {}.

Implementing this trait for a type will automatically implement the ToString trait for the type, allowing the usage of the .to_string() method. Prefer implementing the Display trait for a type, rather than ToString.

Display is similar to Debug, but Display is for user-facing output, and so cannot be derived.

For more information on formatters, see the module-level documentation.

§Completeness and parseability

Display for a type might not necessarily be a lossless or complete representation of the type. It may omit internal state, precision, or other information the type does not consider important for user-facing output, as determined by the type. As such, the output of Display might not be possible to parse, and even if it is, the result of parsing might not exactly match the original value.

However, if a type has a lossless Display implementation whose output is meant to be conveniently machine-parseable and not just meant for human consumption, then the type may wish to accept the same format in FromStr, and document that usage. Having both Display and FromStr implementations where the result of Display cannot be parsed with FromStr may surprise users.

§Internationalization

Because a type can only have one Display implementation, it is often preferable to only implement Display when there is a single most “obvious” way that values can be formatted as text. This could mean formatting according to the “invariant” culture and “undefined” locale, or it could mean that the type display is designed for a specific culture/locale, such as developer logs.

If not all values have a justifiably canonical textual format or if you want to support alternative formats not covered by the standard set of possible formatting traits, the most flexible approach is display adapters: methods like str::escape_default or Path::display which create a wrapper implementing Display to output the specific display format.

§Examples

Implementing Display on a type:

use std::fmt;

struct Point {
    x: i32,
    y: i32,
}

impl fmt::Display for Point {
    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
        write!(f, "({}, {})", self.x, self.y)
    }
}

let origin = Point { x: 0, y: 0 };

assert_eq!(format!("The origin is: {origin}"), "The origin is: (0, 0)");

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::Display for Position {
    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
        write!(f, "({}, {})", self.longitude, self.latitude)
    }
}

assert_eq!(
    "(1.987, 2.983)",
    format!("{}", Position { longitude: 1.987, latitude: 2.983, }),
);

Display

Trait Display Copy item path

§Completeness and parseability

§Internationalization

§Examples

Required Methods§

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

§Errors

§Examples

Implementors§

impl Display for vrl::cli::Error

impl Display for EncodingError

impl Display for FatalError

impl Display for InternalError

impl Display for vrl::datadog_grok::parse_grok_rules::Error

impl Display for ComparisonValue

impl Display for Note

impl Display for vrl::parser::ast::Assignment

impl Display for AssignmentOp

impl Display for AssignmentTarget

impl Display for vrl::parser::ast::Container

impl Display for vrl::parser::ast::Expr

impl Display for vrl::parser::ast::Literal

impl Display for vrl::parser::ast::Opcode

impl Display for vrl::parser::ast::Predicate

impl Display for QueryTarget

impl Display for RootExpr

impl Display for vrl::parser::ast::Unary

impl Display for vrl::parser::Error

impl Display for StringSegment

impl Display for OwnedSegment

impl Display for PathParseError

impl Display for PathPrefix

impl Display for vrl::value::value::Value

impl Display for ConversionError

impl Display for vrl::compiler::conversion::Error

impl Display for ExpressionError

impl Display for VrlRuntime

impl Display for vrl::compiler::expression::Expr

impl Display for vrl::compiler::expression::Literal

impl Display for Target

impl Display for vrl::compiler::function::Error

impl Display for Terminate

impl Display for ValueError

impl Display for AsciiChar

impl Display for Infallible

impl Display for FromBytesWithNulError

impl Display for IpAddr

impl Display for SocketAddr

impl Display for core::slice::GetDisjointMutError

impl Display for VarError

impl Display for std::fs::TryLockError

impl Display for std::io::error::ErrorKind

impl Display for RecvTimeoutError

impl Display for std::sync::mpsc::TryRecvError

impl Display for RoundingError

impl Display for chrono::weekday::Weekday

impl Display for AnyIpCidr

impl Display for IpCidr

impl Display for InetTupleError

impl Display for NetworkParseError

impl Display for IpInet

impl Display for IpInetPair

impl Display for FromHexError

impl Display for IpNet

impl Display for log::Level

impl Display for log::LevelFilter

impl Display for SetFieldError

impl Display for prost_reflect::dynamic::Value

impl Display for DurationError

impl Display for TimestampError

impl Display for DeserializerError

impl Display for SerializerError

impl Display for serde_json::value::Value

impl Display for url::parser::ParseError

impl Display for SyntaxViolation

impl Display for uuid::Variant

impl Display for rand::distr::bernoulli::BernoulliError

impl Display for rand::distr::uniform::Error

impl Display for rand::distr::weighted::Error

Trait Display