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
sourcepub fn description(&self) -> &str
pub fn description(&self) -> &str
use the Display impl or to_string()
impl Error for FromFloatSecsError
1.9.0 · sourceimpl Error for DecodeUtf16Error
impl Error for DecodeUtf16Error
sourcepub fn description(&self) -> &str
pub fn description(&self) -> &str
use the Display impl or to_string()
1.15.0 · sourceimpl Error for RecvTimeoutError
impl Error for RecvTimeoutError
sourcepub fn description(&self) -> &str
pub fn description(&self) -> &str
use the Display impl or to_string()
sourceimpl Error for RecvError
impl Error for RecvError
sourcepub fn description(&self) -> &str
pub fn description(&self) -> &str
use the Display impl or to_string()
1.17.0 · sourceimpl Error for FromBytesWithNulError
impl Error for FromBytesWithNulError
sourcepub fn description(&self) -> &str
pub fn description(&self) -> &str
use the Display impl or to_string()
1.13.0 · sourceimpl Error for BorrowError
impl Error for BorrowError
sourcepub fn description(&self) -> &str
pub fn description(&self) -> &str
use the Display impl or to_string()
1.7.0 · sourceimpl Error for IntoStringError
impl Error for IntoStringError
1.34.0 · sourceimpl Error for TryFromIntError
impl Error for TryFromIntError
sourcepub fn description(&self) -> &str
pub fn description(&self) -> &str
use the Display impl or to_string()
sourceimpl Error for VarError
impl Error for VarError
sourcepub fn description(&self) -> &str
pub fn description(&self) -> &str
use the Display impl or to_string()
impl Error for TryReserveError
1.8.0 · sourceimpl Error for SystemTimeError
impl Error for SystemTimeError
sourcepub fn description(&self) -> &str
pub fn description(&self) -> &str
use the Display impl or to_string()
impl Error for AccessError
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,
sourcepub fn description(&self) -> &str
pub fn description(&self) -> &str
use the Display impl or to_string()
impl Error for LayoutError
1.52.0 · sourceimpl<T> Error for Arc<T> where
T: Error + ?Sized,
impl<T> Error for Arc<T> where
T: Error + ?Sized,
sourceimpl Error for ParseBoolError
impl Error for ParseBoolError
sourcepub fn description(&self) -> &str
pub fn description(&self) -> &str
use the Display impl or to_string()
impl Error for FromVecWithNulError
impl Error for !
sourceimpl Error for Utf8Error
impl Error for Utf8Error
sourcepub fn description(&self) -> &str
pub fn description(&self) -> &str
use the Display impl or to_string()
1.4.0 · sourceimpl Error for AddrParseError
impl Error for AddrParseError
sourcepub fn description(&self) -> &str
pub fn description(&self) -> &str
use the Display impl or to_string()
sourceimpl<T> Error for PoisonError<T>
impl<T> Error for PoisonError<T>
sourcepub fn description(&self) -> &str
pub fn description(&self) -> &str
use the Display impl or to_string()
impl Error for ExitStatusError
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,
sourcepub fn description(&self) -> &str
pub fn description(&self) -> &str
use the Display impl or to_string()
impl Error for AllocError
sourceimpl<T> Error for TrySendError<T> where
T: Send,
impl<T> Error for TrySendError<T> where
T: Send,
sourcepub fn description(&self) -> &str
pub fn description(&self) -> &str
use the Display impl or to_string()
sourceimpl Error for FromUtf16Error
impl Error for FromUtf16Error
sourcepub fn description(&self) -> &str
pub fn description(&self) -> &str
use the Display impl or to_string()
1.13.0 · sourceimpl Error for BorrowMutError
impl Error for BorrowMutError
sourcepub fn description(&self) -> &str
pub 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,
sourcepub fn description(&self) -> &str
pub fn description(&self) -> &str
use the Display impl or to_string()
sourceimpl Error for ParseFloatError
impl Error for ParseFloatError
sourcepub fn description(&self) -> &str
pub fn description(&self) -> &str
use the Display impl or to_string()
1.8.0 · sourceimpl Error for Infallible
impl Error for Infallible
sourcepub fn description(&self) -> &str
pub fn description(&self) -> &str
use the Display impl or to_string()
1.34.0 · sourceimpl Error for TryFromSliceError
impl Error for TryFromSliceError
sourcepub fn description(&self) -> &str
pub 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,
sourcepub fn description(&self) -> &str
pub fn description(&self) -> &str
use the Display impl or to_string()
sourceimpl Error for JoinPathsError
impl Error for JoinPathsError
sourcepub fn description(&self) -> &str
pub fn description(&self) -> &str
use the Display impl or to_string()
sourceimpl Error for TryRecvError
impl Error for TryRecvError
sourcepub fn description(&self) -> &str
pub fn description(&self) -> &str
use the Display impl or to_string()
sourceimpl Error for FromUtf8Error
impl Error for FromUtf8Error
sourcepub fn description(&self) -> &str
pub fn description(&self) -> &str
use the Display impl or to_string()
sourceimpl Error for NulError
impl Error for NulError
sourcepub fn description(&self) -> &str
pub fn description(&self) -> &str
use the Display impl or to_string()
1.34.0 · sourceimpl Error for CharTryFromError
impl Error for CharTryFromError
sourcepub fn description(&self) -> &str
pub fn description(&self) -> &str
use the Display impl or to_string()
impl Error for TryFromCharError
sourceimpl<T> Error for TryLockError<T>
impl<T> Error for TryLockError<T>
sourceimpl Error for ParseIntError
impl Error for ParseIntError
sourcepub fn description(&self) -> &str
pub fn description(&self) -> &str
use the Display impl or to_string()
1.20.0 · sourceimpl Error for ParseCharError
impl Error for ParseCharError
sourcepub fn description(&self) -> &str
pub fn description(&self) -> &str
use the Display impl or to_string()
1.56.0 · sourceimpl Error for WriterPanicked
impl Error for WriterPanicked
sourcepub fn description(&self) -> &str
pub fn description(&self) -> &str
use the Display impl or to_string()
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,
1.11.0 · sourceimpl Error for Error
impl Error for Error
sourcepub fn description(&self) -> &str
pub fn description(&self) -> &str
use the Display impl or to_string()
impl Error for ParseLevelFilterError
impl Error for ParseLevelError
impl Error for SetGlobalDefaultError
impl Error for HoloHashError
sourceimpl Error for RoundingError
impl Error for RoundingError
sourcepub fn description(&self) -> &str
pub fn description(&self) -> &str
use the Display impl or to_string()
sourceimpl Error for ParseError
impl Error for ParseError
sourcepub fn description(&self) -> &str
pub fn description(&self) -> &str
use the Display impl or to_string()
sourceimpl Error for ParseError
impl Error for ParseError
sourcepub fn description(&self) -> &str
pub fn description(&self) -> &str
use the Display impl or to_string()
sourceimpl Error for OutOfRangeError
impl Error for OutOfRangeError
sourcepub fn description(&self) -> &str
pub fn description(&self) -> &str
use the Display impl or to_string()