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.

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

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 + Sync + 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

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 + Sync + Send

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

where T: Error + 'static,

Attempts to downcast the box to a concrete type.

Trait Implementations

impl AsRef<dyn Error> for Error

fn as_ref(&self) -> &(dyn Error + 'static)

Converts this type into a shared reference of the (usually inferred) input type.

impl AsRef<dyn Error + Sync + Send> for Error

fn as_ref(&self) -> &(dyn Error + Sync + Send + 'static)

Converts this type into a shared reference of the (usually inferred) input type.

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

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

Converts a str into a box of dyn Error.

Examples

use std::error::Error;

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

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

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

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

Examples

use std::error::Error;

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

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

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::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!(size_of::<Box<dyn Error>>() == size_of_val(&a_boxed_error))

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

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

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

Examples

use std::error::Error;
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!(
    size_of::<Box<dyn Error + Send + Sync>>() == size_of_val(&a_boxed_error))

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

where E: Error + 'a,

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;

#[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 == size_of_val(&an_error));
let a_boxed_error = Box::<dyn Error>::from(an_error);
assert!(size_of::<Box<dyn Error>>() == size_of_val(&a_boxed_error))

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

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

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

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

Examples

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

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

impl From<Error> for Box<dyn Error>

fn from(error: Error) -> Box<dyn Error>

Converts to this type from the input type.

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

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

Converts to this type from the input type.

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

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

Converts to this type from the input type.

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

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

Converts a String into a box of dyn Error.

Examples

use std::error::Error;

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

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

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

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

Examples

use std::error::Error;

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

impl Value for dyn Error

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

Visits this value with the given Visitor.

impl Value for dyn Error + Send

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

Visits this value with the given Visitor.

impl Value for dyn Error + Sync + Send

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

Visits this value with the given Visitor.

impl Value for dyn Error + Sync

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

Visits this value with the given Visitor.

Implementors

impl !Error for &str

impl Error for llm_tools::secret::Error

impl Error for Infallible

impl Error for FromBytesWithNulError

impl Error for llm_tools::ser::core::slice::GetDisjointMutError

impl Error for VarError

impl Error for std::fs::TryLockError

impl Error for RecvTimeoutError

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

impl Error for ParseAlphabetError

impl Error for base64::decode::DecodeError

impl Error for DecodeSliceError

impl Error for EncodeSliceError

impl Error for dotenv::errors::Error

impl Error for httparse::Error

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

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

impl Error for PreferencesParseError

impl Error for indexmap::GetDisjointMutError

impl Error for APIError

impl Error for BernoulliError

impl Error for WeightedError

impl Error for rustls_pki_types::pem::Error

impl Error for serde_urlencoded::ser::Error

impl Error for tinystr::error::ParseError

impl Error for tokio_socks::error::Error

impl Error for AnyDelimiterCodecError

impl Error for LinesCodecError

impl Error for TryAcquireError

impl Error for tokio::sync::broadcast::error::RecvError

impl Error for tokio::sync::broadcast::error::TryRecvError

impl Error for tokio::sync::mpsc::error::TryRecvError

impl Error for tokio::sync::oneshot::error::TryRecvError

impl Error for CapacityError

impl Error for tungstenite::error::Error

impl Error for ProtocolError

impl Error for SubProtocolError

impl Error for TlsError

impl Error for UrlError

impl Error for url::parser::ParseError

impl Error for ZeroTrieBuildError

impl Error for UleError

impl Error for !

impl Error for llm_tools::ser::serde::de::value::Error

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 llm_tools::ser::core::fmt::Error

impl Error for llm_tools::ser::core::net::AddrParseError

impl Error for ParseFloatError

impl Error for ParseIntError

impl Error for TryFromIntError

impl Error for ParseBoolError

impl Error for Utf8Error

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 WriterPanicked

impl Error for std::io::error::Error

impl Error for NormalizeError

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 TryGetError

impl Error for FromPathBufError

impl Error for FromPathError

impl Error for InvalidLength

impl Error for data_encoding::DecodeError

impl Error for SpecificationError

impl Error for InvalidBufferSize

impl Error for InvalidOutputSize

impl Error for futures_channel::mpsc::SendError

impl Error for futures_channel::mpsc::TryRecvError

impl Error for Canceled

impl Error for SpawnError

impl Error for Aborted

impl Error for getrandom::error::Error

impl Error for h2::error::Error

impl Error for LengthLimitError

impl Error for http::error::Error

impl Error for MaxSizeReached

impl Error for InvalidHeaderName

impl Error for InvalidHeaderValue

impl Error for ToStrError

impl Error for InvalidMethod

impl Error for InvalidStatusCode

impl Error for InvalidUri

impl Error for InvalidUriParts

impl Error for hyper_util::client::legacy::client::Error

impl Error for InvalidNameError

impl Error for hyper::error::Error

impl Error for DataError

impl Error for Errors

impl Error for indexmap::TryReserveError

impl Error for PrefixLenError

impl Error for ipnet::parser::AddrParseError

impl Error for CapacityOverflowError

impl Error for iri_string::normalize::error::Error

impl Error for iri_string::template::error::Error

impl Error for iri_string::validate::Error

impl Error for FromStrError

impl Error for native_tls::Error

impl Error for openssl::error::Error

impl Error for ErrorStack

impl Error for openssl::ssl::error::Error

impl Error for X509VerifyResult

impl Error for ReadError

impl Error for rand_core::error::Error

impl Error for reqwest::error::Error

impl Error for rustls_pki_types::server_name::AddrParseError

impl Error for InvalidDnsNameError

impl Error for serde_json::error::Error

impl Error for LengthDelimitedCodecError

impl Error for tokio::net::tcp::split_owned::ReuniteError

impl Error for tokio::net::unix::split_owned::ReuniteError

impl Error for TryCurrentError

impl Error for JoinError

impl Error for AcquireError

impl Error for tokio::sync::mutex::TryLockError

impl Error for tokio::sync::oneshot::error::RecvError

impl Error for tokio::sync::watch::error::RecvError

impl Error for tokio::time::error::Elapsed

impl Error for tokio::time::error::Error

impl Error for tower::timeout::error::Elapsed

impl Error for None

impl Error for SetGlobalDefaultError

impl Error for ParseLevelError

impl Error for ParseLevelFilterError

impl<'a> Error for utf8::DecodeError<'a>

impl<'a> Error for BufReadDecoderError<'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<A, S, V> Error for ConvertError<A, S, V>

where A: Display + Debug, S: Display + Debug, V: Display + Debug,

impl<E> Error for Box<E>

where E: Error,

impl<L, R> Error for Either<L, R>

where L: Error, R: Error,

Either implements Error if both L and R implement it.

Requires crate feature "std"

impl<Role> Error for tungstenite::handshake::HandshakeError<Role>

where Role: HandshakeRole,

impl<S> Error for native_tls::HandshakeError<S>

where S: Any + Debug,

impl<S> Error for openssl::ssl::error::HandshakeError<S>

where S: Debug,

impl<Src, Dst> Error for AlignmentError<Src, Dst>

where Src: Deref, Dst: KnownLayout + ?Sized,

impl<Src, Dst> Error for SizeError<Src, Dst>

where Src: Deref, Dst: KnownLayout + ?Sized,

impl<Src, Dst> Error for ValidityError<Src, Dst>

where Src: Deref, Dst: KnownLayout + TryFromBytes + ?Sized,

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 tokio::sync::mpsc::error::SendTimeoutError<T>

impl<T> Error for tokio::sync::mpsc::error::TrySendError<T>

impl<T> Error for SetError<T>

where T: Debug,

impl<T> Error for ThinBox<T>

where T: Error + ?Sized,

impl<T> Error for Arc<T>

where T: Error + ?Sized,

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

impl<T> Error for PoisonError<T>

impl<T> Error for futures_channel::mpsc::TrySendError<T>

where T: Any,

impl<T> Error for iri_string::template::error::CreationError<T>

where T: Debug,

impl<T> Error for iri_string::types::generic::error::CreationError<T>

where T: Debug,

impl<T> Error for PollSendError<T>

where T: Debug,

impl<T> Error for AsyncFdTryNewError<T>

impl<T> Error for tokio::sync::broadcast::error::SendError<T>

where T: Debug,

impl<T> Error for tokio::sync::mpsc::error::SendError<T>

impl<T> Error for tokio::sync::watch::error::SendError<T>

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

where E: Debug + Display,

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

where E: Debug + Display,

impl<T, Item> Error for futures_util::stream::stream::split::ReuniteError<T, Item>

where T: Any,

impl<W> Error for IntoInnerError<W>

where W: Send + Debug,