Trait Error

1.0.0 · Source

pub trait Error: Debug + Display {
    // Provided methods
    fn source(&self) -> Option<&(dyn Error + 'static)> { ... }
    fn description(&self) -> &str { ... }
    fn cause(&self) -> Option<&dyn Error> { ... }
    fn provide<'a>(&'a self, request: &mut Request<'a>) { ... }
}

Expand description

Error is a trait representing the basic expectations for error values, i.e., values of type E in Result<T, E>.

Errors must describe themselves through the Display and Debug traits. Error messages are typically concise lowercase sentences without trailing punctuation:

let err = "NaN".parse::<u32>().unwrap_err();
assert_eq!(err.to_string(), "invalid digit found in string");

§Error source

Errors may provide cause information. Error::source() is generally used when errors cross “abstraction boundaries”. If one module must report an error that is caused by an error from a lower-level module, it can allow accessing that error via Error::source(). This makes it possible for the high-level module to provide its own errors while also revealing some of the implementation for debugging.

In error types that wrap an underlying error, the underlying error should be either returned by the outer error’s Error::source(), or rendered by the outer error’s Display implementation, but not both.

§Example

Implementing the Error trait only requires that Debug and Display are implemented too.

use std::error::Error;
use std::fmt;
use std::path::PathBuf;

#[derive(Debug)]
struct ReadConfigError {
    path: PathBuf
}

impl fmt::Display for ReadConfigError {
    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
        let path = self.path.display();
        write!(f, "unable to read configuration at {path}")
    }
}

impl Error for ReadConfigError {}

Provided Methods§

1.30.0 · Source

fn source(&self) -> Option<&(dyn Error + 'static)>

Returns the lower-level source of this error, if any.

§Examples

use std::error::Error;
use std::fmt;

#[derive(Debug)]
struct SuperError {
    source: SuperErrorSideKick,
}

impl fmt::Display for SuperError {
    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
        write!(f, "SuperError is here!")
    }
}

impl Error for SuperError {
    fn source(&self) -> Option<&(dyn Error + 'static)> {
        Some(&self.source)
    }
}

#[derive(Debug)]
struct SuperErrorSideKick;

impl fmt::Display for SuperErrorSideKick {
    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
        write!(f, "SuperErrorSideKick is here!")
    }
}

impl Error for SuperErrorSideKick {}

fn get_super_error() -> Result<(), SuperError> {
    Err(SuperError { source: SuperErrorSideKick })
}

fn main() {
    match get_super_error() {
        Err(e) => {
            println!("Error: {e}");
            println!("Caused by: {}", e.source().unwrap());
        }
        _ => println!("No error"),
    }
}

1.0.0 · Source

fn description(&self) -> &str

👎Deprecated since 1.42.0: use the Display impl or to_string()

if let Err(e) = "xc".parse::<u32>() {
    // Print `e` itself, no need for description().
    eprintln!("Error: {e}");
}

1.0.0 · Source

fn cause(&self) -> Option<&dyn Error>

👎Deprecated since 1.33.0: replaced by Error::source, which can support downcasting

Source

fn provide<'a>(&'a self, request: &mut Request<'a>)

🔬This is a nightly-only experimental API. (error_generic_member_access)

Provides type-based access to context intended for error reports.

Used in conjunction with Request::provide_value and Request::provide_ref to extract references to member variables from dyn Error trait objects.

§Example

#![feature(error_generic_member_access)]
use core::fmt;
use core::error::{request_ref, Request};

#[derive(Debug)]
enum MyLittleTeaPot {
    Empty,
}

#[derive(Debug)]
struct MyBacktrace {
    // ...
}

impl MyBacktrace {
    fn new() -> MyBacktrace {
        // ...
    }
}

#[derive(Debug)]
struct Error {
    backtrace: MyBacktrace,
}

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

impl std::error::Error for Error {
    fn provide<'a>(&'a self, request: &mut Request<'a>) {
        request
            .provide_ref::<MyBacktrace>(&self.backtrace);
    }
}

fn main() {
    let backtrace = MyBacktrace::new();
    let error = Error { backtrace };
    let dyn_error = &error as &dyn std::error::Error;
    let backtrace_ref = request_ref::<MyBacktrace>(dyn_error).unwrap();

    assert!(core::ptr::eq(&error.backtrace, backtrace_ref));
    assert!(request_ref::<MyLittleTeaPot>(dyn_error).is_none());
}

Error

Trait Error Copy item path

§Error source

§Example

Provided Methods§

fn source(&self) -> Option<&(dyn Error + 'static)>

§Examples

fn description(&self) -> &str

fn cause(&self) -> Option<&dyn Error>

fn provide<'a>(&'a self, request: &mut Request<'a>)

§Example

Implementations§

impl dyn Error

pub fn is<T>(&self) -> boolwhere T: Error + 'static,

pub fn downcast_ref<T>(&self) -> Option<&T>where T: Error + 'static,

pub fn downcast_mut<T>(&mut self) -> Option<&mut T>where T: Error + 'static,

impl dyn Error + Send

pub fn is<T>(&self) -> boolwhere T: Error + 'static,

pub fn downcast_ref<T>(&self) -> Option<&T>where T: Error + 'static,

pub fn downcast_mut<T>(&mut self) -> Option<&mut T>where T: Error + 'static,

impl dyn Error + Send + Sync

pub fn is<T>(&self) -> boolwhere T: Error + 'static,

pub fn downcast_ref<T>(&self) -> Option<&T>where T: Error + 'static,

pub fn downcast_mut<T>(&mut self) -> Option<&mut T>where T: Error + 'static,

impl dyn Error

pub fn sources(&self) -> Source<'_>

§Examples

impl dyn Error

pub fn downcast<T>(self: Box<dyn Error>) -> Result<Box<T>, Box<dyn Error>>where T: Error + 'static,

impl dyn Error + Send

pub fn downcast<T>( self: Box<dyn Error + Send>, ) -> Result<Box<T>, Box<dyn Error + Send>>where T: Error + 'static,

impl dyn Error + Send + Sync

pub fn downcast<T>( self: Box<dyn Error + Send + Sync>, ) -> Result<Box<T>, Box<dyn Error + Send + Sync>>where T: Error + 'static,

Implementors§

impl !Error for &str

impl Error for ParseAlphabetError

impl Error for base64::decode::DecodeError

impl Error for DecodeSliceError

impl Error for EncodeSliceError

impl Error for RoundingError

impl Error for crossbeam_channel::err::RecvTimeoutError

impl Error for crossbeam_channel::err::TryRecvError

impl Error for ConnectionError

impl Error for diesel::result::Error

impl Error for humantime::date::Error

impl Error for humantime::duration::Error

impl Error for LinuxI2CError

impl Error for GetTimezoneError

impl Error for icu_collections::codepointtrie::error::Error

impl Error for icu_locale_core::parser::errors::ParseError

impl Error for PreferencesParseError

impl Error for nix::errno::consts::Errno

impl Error for rand::distr::bernoulli::BernoulliError

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

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

impl Error for rand::distributions::bernoulli::BernoulliError

impl Error for rand::distributions::weighted::WeightedError

impl Error for rand::distributions::weighted_index::WeightedError

impl Error for regex::error::Error

impl Error for StartError

impl Error for regex_syntax::error::Error

impl Error for EarlyDataError

impl Error for rustls::conn::unbuffered::EncodeError

impl Error for EncryptError

impl Error for rustls::error::Error

impl Error for VerifierBuilderError

impl Error for rustls_pki_types::pem::Error

impl Error for BetaError

impl Error for BinomialError

impl Error for CategoricalError

impl Error for CauchyError

impl Error for ChiError

impl Error for DiracError

impl Error for DirichletError

impl Error for DiscreteUniformError

impl Error for ExpError

impl Error for FisherSnedecorError

impl Error for GammaError

impl Error for GeometricError

impl Error for GumbelError

Trait Error

pub fn is<T>(&self) -> bool
where T: Error + 'static,

pub fn downcast_ref<T>(&self) -> Option<&T>
where T: Error + 'static,

pub fn downcast_mut<T>(&mut self) -> Option<&mut T>
where T: Error + 'static,

pub fn is<T>(&self) -> bool
where T: Error + 'static,

pub fn downcast_ref<T>(&self) -> Option<&T>
where T: Error + 'static,

pub fn downcast_mut<T>(&mut self) -> Option<&mut T>
where T: Error + 'static,

pub fn is<T>(&self) -> bool
where T: Error + 'static,

pub fn downcast_ref<T>(&self) -> Option<&T>
where T: Error + 'static,

pub fn downcast_mut<T>(&mut self) -> Option<&mut T>
where T: Error + 'static,

pub fn downcast<T>(self: Box<dyn Error>) -> Result<Box<T>, Box<dyn Error>>
where T: Error + 'static,

pub fn downcast<T>( self: Box<dyn Error + Send>, ) -> Result<Box<T>, Box<dyn Error + Send>>
where T: Error + 'static,

pub fn downcast<T>( self: Box<dyn Error + Send + Sync>, ) -> Result<Box<T>, Box<dyn Error + Send + Sync>>
where T: Error + 'static,