pub trait StdError: Debug + Display {
fn source(&self) -> Option<&(dyn Error + 'static)> { ... }
fn backtrace(&self) -> Option<&Backtrace> { ... }
fn description(&self) -> &str { ... }
fn cause(&self) -> Option<&dyn Error> { ... }
}
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");
Errors may provide cause chain 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 via source
chains.
Provided Methods
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"),
}
}
backtrace
)Returns a stack backtrace, if available, of where this error occurred.
This function allows inspecting the location, in code, of where an error
happened. The returned Backtrace
contains information about the stack
trace of the OS thread of execution of where the error originated from.
Note that not all errors contain a Backtrace
. Also note that a
Backtrace
may actually be empty. For more information consult the
Backtrace
type itself.
fn description(&self) -> &str
fn description(&self) -> &str
use the Display impl or to_string()
if let Err(e) = "xc".parse::<u32>() {
// Print `e` itself, no need for description().
eprintln!("Error: {e}");
}
Implementations
sourceimpl dyn Error + 'static
impl dyn Error + 'static
1.3.0 · sourcepub fn is<T>(&self) -> bool where
T: 'static + Error,
pub fn is<T>(&self) -> bool where
T: 'static + Error,
Returns true
if the inner type is the same as T
.
1.3.0 · sourcepub fn downcast_ref<T>(&self) -> Option<&T> where
T: 'static + Error,
pub fn downcast_ref<T>(&self) -> Option<&T> where
T: 'static + Error,
Returns some reference to the inner value if it is of type T
, or
None
if it isn’t.
1.3.0 · sourcepub fn downcast_mut<T>(&mut self) -> Option<&mut T> where
T: 'static + Error,
pub fn downcast_mut<T>(&mut self) -> Option<&mut T> where
T: 'static + Error,
Returns some mutable reference to the inner value if it is of type T
, or
None
if it isn’t.
sourceimpl dyn Error + Send + 'static
impl dyn Error + Send + 'static
1.3.0 · sourcepub fn is<T>(&self) -> bool where
T: 'static + Error,
pub fn is<T>(&self) -> bool where
T: 'static + Error,
Forwards to the method defined on the type dyn Error
.
1.3.0 · sourcepub fn downcast_ref<T>(&self) -> Option<&T> where
T: 'static + Error,
pub fn downcast_ref<T>(&self) -> Option<&T> where
T: 'static + Error,
Forwards to the method defined on the type dyn Error
.
1.3.0 · sourcepub fn downcast_mut<T>(&mut self) -> Option<&mut T> where
T: 'static + Error,
pub fn downcast_mut<T>(&mut self) -> Option<&mut T> where
T: 'static + Error,
Forwards to the method defined on the type dyn Error
.
sourceimpl dyn Error + Send + Sync + 'static
impl dyn Error + Send + Sync + 'static
1.3.0 · sourcepub fn is<T>(&self) -> bool where
T: 'static + Error,
pub fn is<T>(&self) -> bool where
T: 'static + Error,
Forwards to the method defined on the type dyn Error
.
1.3.0 · sourcepub fn downcast_ref<T>(&self) -> Option<&T> where
T: 'static + Error,
pub fn downcast_ref<T>(&self) -> Option<&T> where
T: 'static + Error,
Forwards to the method defined on the type dyn Error
.
1.3.0 · sourcepub fn downcast_mut<T>(&mut self) -> Option<&mut T> where
T: 'static + Error,
pub fn downcast_mut<T>(&mut self) -> Option<&mut T> where
T: 'static + Error,
Forwards to the method defined on the type dyn Error
.
sourceimpl dyn Error + 'static
impl dyn Error + 'static
1.3.0 · sourcepub fn downcast<T>(
self: Box<dyn Error + 'static, Global>
) -> Result<Box<T, Global>, Box<dyn Error + 'static, Global>> where
T: 'static + Error,
pub fn downcast<T>(
self: Box<dyn Error + 'static, Global>
) -> Result<Box<T, Global>, Box<dyn Error + 'static, Global>> where
T: 'static + Error,
Attempts to downcast the box to a concrete type.
sourcepub fn chain(&self) -> Chain<'_>
🔬 This is a nightly-only experimental API. (error_iter
)
pub fn chain(&self) -> Chain<'_>
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.chain();
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());
Trait Implementations
Implementations on Foreign Types
1.7.0 · sourceimpl Error for StripPrefixError
impl Error for StripPrefixError
sourcefn description(&self) -> &str
fn description(&self) -> &str
use the Display impl or to_string()
1.13.0 · sourceimpl Error for BorrowMutError
impl Error for BorrowMutError
sourcefn description(&self) -> &str
fn description(&self) -> &str
use the Display impl or to_string()
sourceimpl Error for ParseFloatError
impl Error for ParseFloatError
sourcefn description(&self) -> &str
fn description(&self) -> &str
use the Display impl or to_string()
sourceimpl Error for JoinPathsError
impl Error for JoinPathsError
sourcefn description(&self) -> &str
fn description(&self) -> &str
use the Display impl or to_string()
1.13.0 · sourceimpl Error for BorrowError
impl Error for BorrowError
sourcefn description(&self) -> &str
fn description(&self) -> &str
use the Display impl or to_string()
impl Error for LayoutError
1.17.0 · sourceimpl Error for FromBytesWithNulError
impl Error for FromBytesWithNulError
sourcefn description(&self) -> &str
fn description(&self) -> &str
use the Display impl or to_string()
sourceimpl<T> Error for TryLockError<T>
impl<T> Error for TryLockError<T>
1.20.0 · sourceimpl Error for ParseCharError
impl Error for ParseCharError
sourcefn description(&self) -> &str
fn description(&self) -> &str
use the Display impl or to_string()
impl Error for ExitStatusError
sourceimpl<T> Error for TrySendError<T> where
T: Send,
impl<T> Error for TrySendError<T> where
T: Send,
sourcefn description(&self) -> &str
fn description(&self) -> &str
use the Display impl or to_string()
sourceimpl Error for RecvError
impl Error for RecvError
sourcefn description(&self) -> &str
fn description(&self) -> &str
use the Display impl or to_string()
impl Error for AllocError
1.34.0 · sourceimpl Error for TryFromIntError
impl Error for TryFromIntError
sourcefn description(&self) -> &str
fn description(&self) -> &str
use the Display impl or to_string()
sourceimpl Error for NulError
impl Error for NulError
sourcefn description(&self) -> &str
fn description(&self) -> &str
use the Display impl or to_string()
1.15.0 · sourceimpl Error for RecvTimeoutError
impl Error for RecvTimeoutError
sourcefn description(&self) -> &str
fn description(&self) -> &str
use the Display impl or to_string()
1.34.0 · sourceimpl Error for CharTryFromError
impl Error for CharTryFromError
sourcefn description(&self) -> &str
fn description(&self) -> &str
use the Display impl or to_string()
sourceimpl<T> Error for PoisonError<T>
impl<T> Error for PoisonError<T>
sourcefn description(&self) -> &str
fn description(&self) -> &str
use the Display impl or to_string()
1.9.0 · sourceimpl Error for DecodeUtf16Error
impl Error for DecodeUtf16Error
sourcefn description(&self) -> &str
fn description(&self) -> &str
use the Display impl or to_string()
1.34.0 · sourceimpl Error for TryFromSliceError
impl Error for TryFromSliceError
sourcefn description(&self) -> &str
fn description(&self) -> &str
use the Display impl or to_string()
sourceimpl<W> Error for IntoInnerError<W> where
W: Send + Debug,
impl<W> Error for IntoInnerError<W> where
W: Send + Debug,
sourcefn description(&self) -> &str
fn description(&self) -> &str
use the Display impl or to_string()
sourceimpl Error for TryRecvError
impl Error for TryRecvError
sourcefn description(&self) -> &str
fn description(&self) -> &str
use the Display impl or to_string()
impl Error for AccessError
1.51.0 · sourceimpl<'a, T> Error for &'a T where
T: Error + ?Sized,
impl<'a, T> Error for &'a T where
T: Error + ?Sized,
1.7.0 · sourceimpl Error for IntoStringError
impl Error for IntoStringError
impl Error for TryFromCharError
sourceimpl Error for Utf8Error
impl Error for Utf8Error
sourcefn description(&self) -> &str
fn description(&self) -> &str
use the Display impl or to_string()
impl Error for TryReserveError
1.4.0 · sourceimpl Error for AddrParseError
impl Error for AddrParseError
sourcefn description(&self) -> &str
fn description(&self) -> &str
use the Display impl or to_string()
sourceimpl Error for VarError
impl Error for VarError
sourcefn description(&self) -> &str
fn description(&self) -> &str
use the Display impl or to_string()
impl Error for FromFloatSecsError
1.52.0 · sourceimpl<T> Error for Arc<T> where
T: Error + ?Sized,
impl<T> Error for Arc<T> where
T: Error + ?Sized,
sourceimpl<'a, K, V> Error for OccupiedError<'a, K, V> where
K: Debug,
V: Debug,
impl<'a, K, V> Error for OccupiedError<'a, K, V> where
K: Debug,
V: Debug,
sourcefn description(&self) -> &str
fn description(&self) -> &str
use the Display impl or to_string()
1.8.0 · sourceimpl Error for SystemTimeError
impl Error for SystemTimeError
sourcefn description(&self) -> &str
fn description(&self) -> &str
use the Display impl or to_string()
sourceimpl Error for FromUtf8Error
impl Error for FromUtf8Error
sourcefn description(&self) -> &str
fn description(&self) -> &str
use the Display impl or to_string()
sourceimpl<T> Error for SendError<T> where
T: Send,
impl<T> Error for SendError<T> where
T: Send,
sourcefn description(&self) -> &str
fn description(&self) -> &str
use the Display impl or to_string()
impl Error for !
sourceimpl Error for ParseIntError
impl Error for ParseIntError
sourcefn description(&self) -> &str
fn description(&self) -> &str
use the Display impl or to_string()
sourceimpl<'a, K, V> Error for OccupiedError<'a, K, V> where
K: Debug + Ord,
V: Debug,
impl<'a, K, V> Error for OccupiedError<'a, K, V> where
K: Debug + Ord,
V: Debug,
sourcefn description(&self) -> &str
fn description(&self) -> &str
use the Display impl or to_string()
impl Error for FromBytesUntilNulError
sourceimpl Error for ParseBoolError
impl Error for ParseBoolError
sourcefn description(&self) -> &str
fn description(&self) -> &str
use the Display impl or to_string()
1.8.0 · sourceimpl Error for Infallible
impl Error for Infallible
sourcefn description(&self) -> &str
fn description(&self) -> &str
use the Display impl or to_string()
1.56.0 · sourceimpl Error for WriterPanicked
impl Error for WriterPanicked
sourcefn description(&self) -> &str
fn description(&self) -> &str
use the Display impl or to_string()
sourceimpl Error for FromUtf16Error
impl Error for FromUtf16Error
sourcefn description(&self) -> &str
fn description(&self) -> &str
use the Display impl or to_string()
impl Error for FromVecWithNulError
1.11.0 · sourceimpl Error for Error
impl Error for Error
sourcefn description(&self) -> &str
fn description(&self) -> &str
use the Display impl or to_string()
impl Error for HoloHashError
impl<E> Error for ValueWriteError<E> where
E: RmpWriteErr,
impl<E> Error for ValueWriteError<E> where
E: RmpWriteErr,
impl<'a, E> Error for DecodeStringError<'a, E> where
E: RmpReadErr,
impl<'a, E> Error for DecodeStringError<'a, E> where
E: RmpReadErr,
impl Error for BytesReadError
impl Error for SecurePrimitiveError
sourceimpl Error for RoundingError
impl Error for RoundingError
sourcefn description(&self) -> &str
fn description(&self) -> &str
use the Display impl or to_string()
sourceimpl Error for ParseError
impl Error for ParseError
sourcefn description(&self) -> &str
fn description(&self) -> &str
use the Display impl or to_string()
sourceimpl Error for OutOfRangeError
impl Error for OutOfRangeError
sourcefn description(&self) -> &str
fn description(&self) -> &str
use the Display impl or to_string()
sourceimpl Error for ParseError
impl Error for ParseError
sourcefn description(&self) -> &str
fn description(&self) -> &str
use the Display impl or to_string()