Trait Error

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>) { ... }
}

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");

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.

Provided Methods

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"),
    }
}

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}");
}

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

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

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());
}

Implementations

impl dyn Error

pub fn is<T>(&self) -> bool

where T: Error + 'static,

Returns true if the inner type is the same as T.

pub fn downcast_ref<T>(&self) -> Option<&T>

where T: Error + 'static,

Returns some reference to the inner value if it is of type T, or None if it isn’t.

pub fn downcast_mut<T>(&mut self) -> Option<&mut T>

where T: Error + 'static,

Returns some mutable reference to the inner value if it is of type T, or None if it isn’t.

impl dyn Error + Send

pub fn is<T>(&self) -> bool

where T: Error + 'static,

Forwards to the method defined on the type dyn Error.

pub fn downcast_ref<T>(&self) -> Option<&T>

where T: Error + 'static,

Forwards to the method defined on the type dyn Error.

pub fn downcast_mut<T>(&mut self) -> Option<&mut T>

where T: Error + 'static,

Forwards to the method defined on the type dyn Error.

impl dyn Error + Send + Sync

pub fn is<T>(&self) -> bool

where T: Error + 'static,

Forwards to the method defined on the type dyn Error.

pub fn downcast_ref<T>(&self) -> Option<&T>

where T: Error + 'static,

Forwards to the method defined on the type dyn Error.

pub fn downcast_mut<T>(&mut self) -> Option<&mut T>

where T: Error + 'static,

Forwards to the method defined on the type dyn Error.

impl dyn Error

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

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

Returns an iterator starting with the current error and continuing with recursively calling Error::source.

If you want to omit the current error and only use its sources, use skip(1).

Examples

#![feature(error_iter)]
use std::error::Error;
use std::fmt;

#[derive(Debug)]
struct A;

#[derive(Debug)]
struct B(Option<Box<dyn Error + 'static>>);

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

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

impl Error for A {}

impl Error for B {
    fn source(&self) -> Option<&(dyn Error + 'static)> {
        self.0.as_ref().map(|e| e.as_ref())
    }
}

let b = B(Some(Box::new(A)));

// let err : Box<Error> = b.into(); // or
let err = &b as &(dyn Error);

let mut iter = err.sources();

assert_eq!("B".to_string(), iter.next().unwrap().to_string());
assert_eq!("A".to_string(), iter.next().unwrap().to_string());
assert!(iter.next().is_none());
assert!(iter.next().is_none());

impl dyn Error

pub fn downcast<T>(self: Box<dyn Error>) -> Result<Box<T>, Box<dyn Error>>

where T: Error + 'static,

Attempts to downcast the box to a concrete type.

impl dyn Error + Send

pub fn downcast<T>( self: Box<dyn Error + Send>, ) -> Result<Box<T>, Box<dyn Error + Send>>

where T: Error + 'static,

Attempts to downcast the box to a concrete type.

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,

Attempts to downcast the box to a concrete type.

Trait Implementations

impl<'a> From<&str> for Box<dyn Error + 'a>

Available on non-no_global_oom_handling only.

fn from(err: &str) -> Box<dyn Error + 'a>

Converts a str into a box of dyn Error.

Examples

use std::error::Error;
use std::mem;

let a_str_error = "a str error";
let a_boxed_error = Box::<dyn Error>::from(a_str_error);
assert!(mem::size_of::<Box<dyn Error>>() == mem::size_of_val(&a_boxed_error))

impl<'a> From<&str> for Box<dyn Error + Send + Sync + 'a>

Available on non-no_global_oom_handling only.

fn from(err: &str) -> Box<dyn Error + Send + Sync + 'a>

Converts a str into a box of dyn Error + Send + Sync.

Examples

use std::error::Error;
use std::mem;

let a_str_error = "a str error";
let a_boxed_error = Box::<dyn Error + Send + Sync>::from(a_str_error);
assert!(
    mem::size_of::<Box<dyn Error + Send + Sync>>() == mem::size_of_val(&a_boxed_error))

impl From<CompactString> for Box<dyn Error>

Available on crate feature std only.

fn from(value: CompactString) -> Box<dyn Error>

Converts to this type from the input type.

impl From<CompactString> for Box<dyn Error + Send + Sync>

Available on crate feature std only.

fn from(value: CompactString) -> Box<dyn Error + Send + Sync>

Converts to this type from the input type.

impl<'a, 'b> From<Cow<'b, str>> for Box<dyn Error + 'a>

Available on non-no_global_oom_handling only.

fn from(err: Cow<'b, str>) -> Box<dyn Error + 'a>

Converts a Cow into a box of dyn Error.

Examples

use std::error::Error;
use std::mem;
use std::borrow::Cow;

let a_cow_str_error = Cow::from("a str error");
let a_boxed_error = Box::<dyn Error>::from(a_cow_str_error);
assert!(mem::size_of::<Box<dyn Error>>() == mem::size_of_val(&a_boxed_error))

impl<'a, 'b> From<Cow<'b, str>> for Box<dyn Error + Send + Sync + 'a>

Available on non-no_global_oom_handling only.

fn from(err: Cow<'b, str>) -> Box<dyn Error + Send + Sync + 'a>

Converts a Cow into a box of dyn Error + Send + Sync.

Examples

use std::error::Error;
use std::mem;
use std::borrow::Cow;

let a_cow_str_error = Cow::from("a str error");
let a_boxed_error = Box::<dyn Error + Send + Sync>::from(a_cow_str_error);
assert!(
    mem::size_of::<Box<dyn Error + Send + Sync>>() == mem::size_of_val(&a_boxed_error))

impl<'a, E> From<E> for Box<dyn Error + 'a>

where E: Error + 'a,

Available on non-no_global_oom_handling only.

fn from(err: E) -> Box<dyn Error + 'a>

Converts a type of Error into a box of dyn Error.

Examples

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

#[derive(Debug)]
struct AnError;

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

impl Error for AnError {}

let an_error = AnError;
assert!(0 == mem::size_of_val(&an_error));
let a_boxed_error = Box::<dyn Error>::from(an_error);
assert!(mem::size_of::<Box<dyn Error>>() == mem::size_of_val(&a_boxed_error))

impl<'a, E> From<E> for Box<dyn Error + Send + Sync + 'a>

where E: Error + Send + Sync + 'a,

Available on non-no_global_oom_handling only.

fn from(err: E) -> Box<dyn Error + Send + Sync + 'a>

Converts a type of Error + Send + Sync into a box of dyn Error + Send + Sync.

Examples

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

#[derive(Debug)]
struct AnError;

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

impl Error for AnError {}

unsafe impl Send for AnError {}

unsafe impl Sync for AnError {}

let an_error = AnError;
assert!(0 == mem::size_of_val(&an_error));
let a_boxed_error = Box::<dyn Error + Send + Sync>::from(an_error);
assert!(
    mem::size_of::<Box<dyn Error + Send + Sync>>() == mem::size_of_val(&a_boxed_error))

impl From<Error> for Box<dyn Error + Send>

fn from(e: Error) -> Box<dyn Error + Send>

Converts to this type from the input type.

impl<'a> From<String> for Box<dyn Error + 'a>

Available on non-no_global_oom_handling only.

fn from(str_err: String) -> Box<dyn Error + 'a>

Converts a String into a box of dyn Error.

Examples

use std::error::Error;
use std::mem;

let a_string_error = "a string error".to_string();
let a_boxed_error = Box::<dyn Error>::from(a_string_error);
assert!(mem::size_of::<Box<dyn Error>>() == mem::size_of_val(&a_boxed_error))

impl<'a> From<String> for Box<dyn Error + Send + Sync + 'a>

Available on non-no_global_oom_handling only.

fn from(err: String) -> Box<dyn Error + Send + Sync + 'a>

Converts a String into a box of dyn Error + Send + Sync.

Examples

use std::error::Error;
use std::mem;

let a_string_error = "a string error".to_string();
let a_boxed_error = Box::<dyn Error + Send + Sync>::from(a_string_error);
assert!(
    mem::size_of::<Box<dyn Error + Send + Sync>>() == mem::size_of_val(&a_boxed_error))

impl Value for dyn Error

Available on crate feature std only.

fn record(&self, key: &Field, visitor: &mut dyn Visit)

Visits this value with the given Visitor.

impl Value for dyn Error + Send

Available on crate feature std only.

fn record(&self, key: &Field, visitor: &mut dyn Visit)

Visits this value with the given Visitor.

impl Value for dyn Error + Send + Sync

Available on crate feature std only.

fn record(&self, key: &Field, visitor: &mut dyn Visit)

Visits this value with the given Visitor.

impl Value for dyn Error + Sync

Available on crate feature std only.

fn record(&self, key: &Field, visitor: &mut dyn Visit)

Visits this value with the given Visitor.

Implementors

impl !Error for &str

impl Error for kvarn::encryption::Error

impl Error for ToCompactStringError

Available on crate feature std only.

impl Error for Infallible

impl Error for VarError

impl Error for std::sync::mpsc::RecvTimeoutError

impl Error for std::sync::mpsc::TryRecvError

impl Error for BernoulliError

Available on crate feature std only.

impl Error for WeightedError

Available on crate feature std only.

impl Error for !

impl Error for kvarn::prelude::utils::prelude::fmt::Error

impl Error for InvalidHeaderName

impl Error for InvalidHeaderValue

impl Error for MaxSizeReached

impl Error for ToStrError

impl Error for kvarn::prelude::utils::prelude::io::Error

impl Error for WriterPanicked

impl Error for kvarn::prelude::utils::prelude::net::AddrParseError

impl Error for ParseBoolError

impl Error for Utf8Error

impl Error for InvalidUri

impl Error for InvalidUriParts

impl Error for ReserveError

Available on crate feature std only.

impl Error for AllocError

impl Error for LayoutError

impl Error for TryFromSliceError

impl Error for BorrowError

impl Error for BorrowMutError

impl Error for CharTryFromError

impl Error for DecodeUtf16Error

impl Error for ParseCharError

impl Error for TryFromCharError

impl Error for FromBytesUntilNulError

impl Error for FromBytesWithNulError

impl Error for ParseFloatError

impl Error for kvarn::prelude::utils::prelude::compact_str::core::num::ParseIntError

impl Error for kvarn::prelude::utils::prelude::compact_str::core::num::TryFromIntError

impl Error for TryFromFloatSecsError

impl Error for UnorderedKeyError

impl Error for alloc::collections::TryReserveError

impl Error for FromVecWithNulError

impl Error for IntoStringError

impl Error for NulError

impl Error for FromUtf8Error

impl Error for FromUtf16Error

impl Error for JoinPathsError

impl Error for StripPrefixError

impl Error for ExitStatusError

impl Error for std::sync::mpsc::RecvError

impl Error for AccessError

impl Error for SystemTimeError

impl Error for CompressError

impl Error for DecompressError

impl Error for getrandom::error::Error

impl Error for log::ParseLevelError

Available on crate feature std only.

impl Error for SetLoggerError

Available on crate feature std only.

impl Error for FromStrError

impl Error for serde::de::value::Error

Available on crate feature std only.

impl Error for uuid::error::Error

impl Error for rand::rngs::adapter::read::ReadError

impl Error for rand_core::error::Error

Available on crate feature std only.

impl Error for Aborted

Available on crate feature std only.

impl Error for AcquireError

impl Error for AddrParseError

Available on crate feature std only.

impl Error for AnyDelimiterCodecError

impl Error for Canceled

Available on crate feature std only.

impl Error for CapacityError

impl Error for ClosedStream

impl Error for ComponentRange

Available on crate feature std only.

impl Error for ConfigError

impl Error for ConnectError

impl Error for ConnectionError

impl Error for ConnectionError

impl Error for ConversionRange

Available on crate feature std only.

impl Error for DecodeError

Available on crate feature std only.

impl Error for DecodeSliceError

Available on crate feature std only.

impl Error for DifferentVariant

Available on crate feature std only.

impl Error for EarlyDataError

Available on crate feature std only.

impl Error for Elapsed

impl Error for EncodeError

Available on crate feature std only.

impl Error for EncodeSliceError

Available on crate feature std only.

impl Error for EncryptError

Available on crate feature std only.

impl Error for EnterError

impl Error for Error

Available on crate feature std only.

impl Error for Error

Available on crate feature std only.

impl Error for Error

Available on crate feature std only.

impl Error for Error

impl Error for Error

impl Error for Error

Available on crate feature std only.

impl Error for Error

impl Error for Error

impl Error for Error

impl Error for Error

impl Error for Error

impl Error for Error

impl Error for Error

impl Error for FinishError

impl Error for Format

Available on crate feature std only.

impl Error for IndeterminateOffset

Available on crate feature std only.

impl Error for InvalidBufferSize

Available on crate feature std only.

impl Error for InvalidDnsNameError

Available on crate feature std only.

impl Error for InvalidFormatDescription

Available on crate feature std only.

impl Error for InvalidLength

Available on crate feature std only.

impl Error for InvalidMethod

impl Error for InvalidOutputSize

Available on crate feature std only.

impl Error for InvalidStatusCode

impl Error for InvalidVariant

Available on crate feature std only.

impl Error for JoinError

impl Error for KeyRejected

Available on crate feature std only.

impl Error for KeyRejected

impl Error for LengthDelimitedCodecError

impl Error for LinesCodecError

impl Error for NoInitialCipherSuite

impl Error for OtherError

Available on crate feature std only.

impl Error for PacketDecodeError

impl Error for Parse

Available on crate feature std only.

impl Error for ParseAlphabetError

Available on crate feature std only.

impl Error for ParseFromDescription

Available on crate feature std only.

impl Error for ParseIntError

Available on crate feature std only.

impl Error for ParseLevelError

Available on crate feature std only.

impl Error for ParseLevelFilterError

Available on crate feature std only.

impl Error for PredicateError

impl Error for ProtocolError

impl Error for PushError

impl Error for ReadError

impl Error for ReadError

impl Error for ReadError

impl Error for ReadExactError

impl Error for ReadToEndError

impl Error for ReadableError

impl Error for RecvError

impl Error for RecvError

impl Error for RecvError

impl Error for RecvError

impl Error for RecvTimeoutError

impl Error for ResetError

impl Error for RetryError

impl Error for RetryError

impl Error for ReuniteError

impl Error for ReuniteError

impl Error for SelectTimeoutError

impl Error for SendDatagramError

impl Error for SendDatagramError

impl Error for SendDatagramError

impl Error for SendError

impl Error for SendStreamError

impl Error for SetGlobalDefaultError

Available on crate feature std only.

impl Error for SpawnError

Available on crate feature std only.

impl Error for StoppedError

impl Error for SubProtocolError

impl Error for TlsError

impl Error for TryAcquireError

impl Error for TryCurrentError

impl Error for TryFromIntError

Available on crate feature std only.

impl Error for TryFromParsed

Available on crate feature std only.

impl Error for TryLockError

impl Error for TryRecvError

impl Error for TryRecvError

impl Error for TryRecvError

impl Error for TryRecvError

impl Error for TryRecvError

impl Error for TryReserveError

Available on crate feature std only.

impl Error for TrySelectError

impl Error for Unspecified

Available on crate feature std only.

impl Error for Unspecified

impl Error for UnsupportedOperationError

Available on crate feature std only.

impl Error for UrlError

impl Error for VarIntBoundsExceeded

impl Error for VerifierBuilderError

Available on crate feature std only.

impl Error for WriteError

impl Error for WriteError

impl<'a> Error for BufReadDecoderError<'a>

impl<'a> Error for DecodeError<'a>

impl<'a, K, V> Error for alloc::collections::btree::map::entry::OccupiedError<'a, K, V>

where K: Debug + Ord, V: Debug,

impl<'a, K, V> Error for std::collections::hash::map::OccupiedError<'a, K, V>

where K: Debug, V: Debug,

impl<'a, T> Error for &'a T

where T: Error + ?Sized,

impl<E> Error for Err<E>

where E: Debug,

Available on crate feature std only.

impl<I> Error for Error<I>

where I: Debug + Display,

Available on crate feature std only.

impl<I> Error for VerboseError<I>

where I: Debug + Display,

Available on crate feature std only.

impl<T> Error for std::sync::mpmc::error::SendTimeoutError<T>

impl<T> Error for std::sync::mpsc::TrySendError<T>

impl<T> Error for std::sync::poison::TryLockError<T>

impl<T> Error for Arc<T>

where T: Error + ?Sized,

impl<T> Error for Box<T>

where T: Error,

impl<T> Error for ThinBox<T>

where T: Error + ?Sized,

impl<T> Error for std::sync::mpsc::SendError<T>

impl<T> Error for PoisonError<T>

impl<T> Error for AsyncFdTryNewError<T>

impl<T> Error for PollSendError<T>

where T: Debug,

impl<T> Error for ReuniteError<T>

where T: Any,

Available on crate feature std only.

impl<T> Error for SendError<T>

impl<T> Error for SendError<T>

impl<T> Error for SendError<T>

where T: Debug,

impl<T> Error for SendError<T>

where T: Send,

impl<T> Error for SendTimeoutError<T>

Available on crate feature time only.

impl<T> Error for SendTimeoutError<T>

where T: Send,

impl<T> Error for SetError<T>

where T: Debug,

impl<T> Error for TrySendError<T>

impl<T> Error for TrySendError<T>

where T: Any,

impl<T> Error for TrySendError<T>

where T: Send,

impl<T, E> Error for TryChunksError<T, E>

where E: Debug + Display,

Available on crate feature std only.

impl<T, E> Error for TryReadyChunksError<T, E>

where E: Debug + Display,

Available on crate feature std only.

impl<T, Item> Error for ReuniteError<T, Item>

where T: Any,

Available on crate feature std only.

impl<W> Error for IntoInnerError<W>

where W: Send + Debug,

impl<const N: usize> Error for GetManyMutError<N>