Trait StdError

pub trait StdError: 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 + 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<'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;
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 + 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;
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<'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::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 + 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::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,

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 + 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;
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<'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;
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 + 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;
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

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 CalendarError

impl Error for FormatError

impl Error for Infallible

impl Error for VarError

impl Error for RecvTimeoutError

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

impl Error for RoundingError

impl Error for FromHexError

impl Error for url::parser::ParseError

impl Error for BernoulliError

impl Error for WeightedError

impl Error for !

impl Error for BlockError

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 LayoutError

impl Error for AllocError

impl Error for TryFromSliceError

impl Error for BorrowError

impl Error for BorrowMutError

impl Error for CharTryFromError

impl Error for ParseCharError

impl Error for DecodeUtf16Error

impl Error for TryFromCharError

impl Error for FromBytesUntilNulError

impl Error for FromBytesWithNulError

impl Error for core::fmt::Error

impl Error for core::net::parser::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 ExpandError

impl Error for proc_macro::LexError

impl Error for JoinPathsError

impl Error for WriterPanicked

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

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 chrono::format::ParseError

impl Error for ParseMonthError

impl Error for OutOfRange

impl Error for OutOfRangeError

impl Error for ParseWeekdayError

impl Error for getrandom::error::Error

impl Error for GlobError

impl Error for PatternError

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 PrefixLenError

impl Error for ipnet::parser::AddrParseError

impl Error for log::ParseLevelError

impl Error for SetLoggerError

impl Error for FromStrError

impl Error for openssl::error::Error

impl Error for ErrorStack

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

impl Error for X509VerifyResult

impl Error for proc_macro2::LexError

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

impl Error for serde_json::error::Error

impl Error for syn::error::Error

impl Error for uuid::error::Error

impl Error for ReadError

impl Error for rand_core::error::Error

impl Error for BoxErrorWrapper

impl Error for i3status_rs::errors::Error

impl Error for Aborted

impl Error for AcquireError

impl Error for AddrParseError

impl Error for AnyDelimiterCodecError

impl Error for AttrError

impl Error for BindError

impl Error for BuildError

impl Error for BuildError

impl Error for BuildError

impl Error for BuildError

impl Error for BuildError

impl Error for CacheError

impl Error for CalibrightError

impl Error for Canceled

impl Error for CaseFoldError

impl Error for Code

impl Error for ConfigurationError

impl Error for ConnectError

impl Error for DatetimeParseError

impl Error for DeError

impl Error for DeError

impl Error for DecodeError

impl Error for DecodeError

impl Error for DecodeError

impl Error for DecodeError

impl Error for DecodeSliceError

impl Error for DecodeSliceError

impl Error for DeserializeError

impl Error for Elapsed

impl Error for EncodeSliceError

impl Error for EncodeSliceError

impl Error for EncodingError

impl Error for EnterError

impl Error for Errno

impl Error for Errno

impl Error for Errno

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 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 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 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 Error

impl Error for Error

impl Error for Error

impl Error for ErrorKind

impl Error for Errors

impl Error for EscapeError

impl Error for GenError

impl Error for GetTimezoneError

impl Error for GroupInfoError

impl Error for IllFormedError

impl Error for InvalidBufferSize

impl Error for InvalidDnsNameError

impl Error for InvalidDnsNameError

impl Error for InvalidLength

impl Error for InvalidNameError

impl Error for InvalidOutputSize

impl Error for JoinError

impl Error for LengthDelimitedCodecError

impl Error for LibsensorsError

impl Error for LinesCodecError

impl Error for MailEntryError

impl Error for MailParseError

impl Error for MaildirError

impl Error for MatchError

impl Error for MatchError

impl Error for MatchesError

impl Error for NamespaceError

impl Error for PAErr

impl Error for ParseAlphabetError

impl Error for ParseAlphabetError

impl Error for ParseCharRefError

impl Error for ParseError

impl Error for ParseError

impl Error for ParseError

impl Error for ParseLevelError

impl Error for ParseLevelFilterError

impl Error for ParseValueError

impl Error for PatternIDError

impl Error for PatternIDError

impl Error for PatternSetInsertError

impl Error for PeekHeaderError

impl Error for PopError

impl Error for QuotedPrintableError

impl Error for RecvError

impl Error for RecvError

impl Error for RecvError

impl Error for RecvError

impl Error for RecvMessageError

impl Error for ReuniteError

impl Error for ReuniteError

impl Error for SeError

impl Error for SendError

impl Error for SerError

impl Error for SerializeError

impl Error for SetGlobalDefaultError

impl Error for SignError

impl Error for SmallIndexError

impl Error for SpawnError

impl Error for SpecificationError

impl Error for StartError

impl Error for StateIDError

impl Error for StateIDError

impl Error for Status

impl Error for SyntaxError

impl Error for TomlError

impl Error for TryAcquireError

impl Error for TryCurrentError

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

impl Error for UnicodeWordBoundaryError

impl Error for UnicodeWordError

impl Error for WrappedError

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 serde_path_to_error::Error<E>

where E: Error,

impl<E> Error for Err<E>

where E: Debug,

impl<E> Error for LookupError<E>

where E: Error + 'static,

impl<F> Error for Error<F>

where F: ErrorFormatter,

impl<I> Error for Error<I>

where I: Debug + Display,

impl<I> Error for ExactlyOneError<I>

where I: Iterator + Debug, <I as Iterator>::Item: Debug,

impl<I> Error for InputError<I>

where I: Clone + Debug + Display + Sync + Send + 'static,

impl<I> Error for VerboseError<I>

where I: Debug + Display,

impl<I, C> Error for TreeError<I, C>

where I: Stream + Clone + Debug + Display + Sync + Send + 'static, C: Display + Debug,

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 "use_std"

impl<RE, T> Error for RequestTokenError<RE, T>

where RE: Error + 'static, T: ErrorResponse + 'static, RequestTokenError<RE, T>: Debug + Display,

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

where S: Debug,

impl<S> Error for HandshakeError<S>

where S: Any + Debug,

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 Box<T>

where T: Error,

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 AsyncFdTryNewError<T>

impl<T> Error for Error<T>

where T: Error + 'static, Error<T>: Debug + Display,

impl<T> Error for ForcePushError<T>

where T: Debug,

impl<T> Error for PollSendError<T>

where T: Debug,

impl<T> Error for PushError<T>

where T: Debug,

impl<T> Error for ReuniteError<T>

where T: Any,

impl<T> Error for SendError<T>

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 SendTimeoutError<T>

impl<T> Error for SetError<T>

where T: Debug,

impl<T> Error for TrySendError<T>

impl<T> Error for TrySendError<T>

impl<T> Error for TrySendError<T>

where T: Any,

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 ReuniteError<T, Item>

where T: Any,

impl<T, P> Error for NlError<T, P>

where T: Debug, P: Debug,

impl<T, P> Error for Nlmsgerr<T, P>

where T: Debug, P: Debug,

impl<W> Error for IntoInnerError<W>

where W: Send + Debug,

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