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, demand: &mut Demand<'a>) { ... }
}
miri-test-libstd
only.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 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§
1.30.0 · sourcefn source(&self) -> Option<&(dyn Error + 'static)>
fn source(&self) -> Option<&(dyn Error + 'static)>
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"),
}
}
sourcefn description(&self) -> &str
fn description(&self) -> &str
if let Err(e) = "xc".parse::<u32>() {
// Print `e` itself, no need for description().
eprintln!("Error: {e}");
}
sourcefn cause(&self) -> Option<&dyn Error>
fn cause(&self) -> Option<&dyn Error>
sourcefn provide<'a>(&'a self, demand: &mut Demand<'a>)
fn provide<'a>(&'a self, demand: &mut Demand<'a>)
error_generic_member_access
)Provides type based access to context intended for error reports.
Used in conjunction with Demand::provide_value
and Demand::provide_ref
to extract
references to member variables from dyn Error
trait objects.
Example
#![feature(provide_any)]
#![feature(error_generic_member_access)]
use core::fmt;
use core::any::Demand;
#[derive(Debug)]
struct MyBacktrace {
// ...
}
impl MyBacktrace {
fn new() -> MyBacktrace {
// ...
}
}
#[derive(Debug)]
struct SourceError {
// ...
}
impl fmt::Display for SourceError {
fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
write!(f, "Example Source Error")
}
}
impl std::error::Error for SourceError {}
#[derive(Debug)]
struct Error {
source: SourceError,
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, demand: &mut Demand<'a>) {
demand
.provide_ref::<MyBacktrace>(&self.backtrace)
.provide_ref::<dyn std::error::Error + 'static>(&self.source);
}
}
fn main() {
let backtrace = MyBacktrace::new();
let source = SourceError {};
let error = Error { source, backtrace };
let dyn_error = &error as &dyn std::error::Error;
let backtrace_ref = dyn_error.request_ref::<MyBacktrace>().unwrap();
assert!(core::ptr::eq(&error.backtrace, backtrace_ref));
}
Implementations§
source§impl<'a> dyn Error + 'a
impl<'a> dyn Error + 'a
sourcepub fn request_ref<T>(&'a self) -> Option<&'a T>where
T: 'static + ?Sized,
🔬This is a nightly-only experimental API. (error_generic_member_access
)
pub fn request_ref<T>(&'a self) -> Option<&'a T>where T: 'static + ?Sized,
error_generic_member_access
)Request a reference of type T
as context about this error.
sourcepub fn request_value<T>(&'a self) -> Option<T>where
T: 'static,
🔬This is a nightly-only experimental API. (error_generic_member_access
)
pub fn request_value<T>(&'a self) -> Option<T>where T: 'static,
error_generic_member_access
)Request a value of type T
as context about this error.
source§impl dyn Error + 'static
impl dyn Error + 'static
1.3.0 · sourcepub fn is<T>(&self) -> boolwhere
T: Error + 'static,
pub fn is<T>(&self) -> boolwhere T: Error + 'static,
Returns true
if the inner type is the same as T
.
1.3.0 · sourcepub fn downcast_ref<T>(&self) -> Option<&T>where
T: Error + 'static,
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.
1.3.0 · sourcepub fn downcast_mut<T>(&mut self) -> Option<&mut T>where
T: Error + 'static,
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.
source§impl dyn Error + Send + 'static
impl dyn Error + Send + 'static
1.3.0 · sourcepub fn is<T>(&self) -> boolwhere
T: Error + 'static,
pub fn is<T>(&self) -> boolwhere T: Error + 'static,
Forwards to the method defined on the type dyn Error
.
1.3.0 · sourcepub fn downcast_ref<T>(&self) -> Option<&T>where
T: Error + 'static,
pub fn downcast_ref<T>(&self) -> Option<&T>where T: Error + 'static,
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: Error + 'static,
pub fn downcast_mut<T>(&mut self) -> Option<&mut T>where T: Error + 'static,
Forwards to the method defined on the type dyn Error
.
sourcepub fn request_ref<T>(&self) -> Option<&T>where
T: 'static + ?Sized,
🔬This is a nightly-only experimental API. (error_generic_member_access
)
pub fn request_ref<T>(&self) -> Option<&T>where T: 'static + ?Sized,
error_generic_member_access
)Request a reference of type T
as context about this error.
sourcepub fn request_value<T>(&self) -> Option<T>where
T: 'static,
🔬This is a nightly-only experimental API. (error_generic_member_access
)
pub fn request_value<T>(&self) -> Option<T>where T: 'static,
error_generic_member_access
)Request a value of type T
as context about this error.
source§impl dyn Error + Sync + Send + 'static
impl dyn Error + Sync + Send + 'static
1.3.0 · sourcepub fn is<T>(&self) -> boolwhere
T: Error + 'static,
pub fn is<T>(&self) -> boolwhere T: Error + 'static,
Forwards to the method defined on the type dyn Error
.
1.3.0 · sourcepub fn downcast_ref<T>(&self) -> Option<&T>where
T: Error + 'static,
pub fn downcast_ref<T>(&self) -> Option<&T>where T: Error + 'static,
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: Error + 'static,
pub fn downcast_mut<T>(&mut self) -> Option<&mut T>where T: Error + 'static,
Forwards to the method defined on the type dyn Error
.
sourcepub fn request_ref<T>(&self) -> Option<&T>where
T: 'static + ?Sized,
🔬This is a nightly-only experimental API. (error_generic_member_access
)
pub fn request_ref<T>(&self) -> Option<&T>where T: 'static + ?Sized,
error_generic_member_access
)Request a reference of type T
as context about this error.
sourcepub fn request_value<T>(&self) -> Option<T>where
T: 'static,
🔬This is a nightly-only experimental API. (error_generic_member_access
)
pub fn request_value<T>(&self) -> Option<T>where T: 'static,
error_generic_member_access
)Request a value of type T
as context about this error.
source§impl dyn Error + 'static
impl dyn Error + 'static
sourcepub fn sources(&self) -> Source<'_> ⓘ
🔬This is a nightly-only experimental API. (error_iter
)
pub fn sources(&self) -> Source<'_> ⓘ
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());
Trait Implementations§
1.6.0 · source§impl From<&str> for Box<dyn Error + 'static, Global>
Available on non-no_global_oom_handling
only.
impl From<&str> for Box<dyn Error + 'static, Global>
no_global_oom_handling
only.source§impl<'a> From<&str> for Box<dyn Error + Sync + Send + 'a, Global>
Available on non-no_global_oom_handling
only.
impl<'a> From<&str> for Box<dyn Error + Sync + Send + 'a, Global>
no_global_oom_handling
only.1.22.0 · source§impl<'a> From<Cow<'a, str>> for Box<dyn Error + 'static, Global>
Available on non-no_global_oom_handling
only.
impl<'a> From<Cow<'a, str>> for Box<dyn Error + 'static, Global>
no_global_oom_handling
only.1.22.0 · source§impl<'a, 'b> From<Cow<'b, str>> for Box<dyn Error + Sync + Send + 'a, Global>
Available on non-no_global_oom_handling
only.
impl<'a, 'b> From<Cow<'b, str>> for Box<dyn Error + Sync + Send + 'a, Global>
no_global_oom_handling
only.source§fn from(err: Cow<'b, str>) -> Box<dyn Error + Sync + Send + 'a, Global>
fn from(err: Cow<'b, str>) -> Box<dyn Error + Sync + Send + 'a, Global>
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))
source§impl<'a, E> From<E> for Box<dyn Error + 'a, Global>where
E: Error + 'a,
Available on non-no_global_oom_handling
only.
impl<'a, E> From<E> for Box<dyn Error + 'a, Global>where E: Error + 'a,
no_global_oom_handling
only.source§fn from(err: E) -> Box<dyn Error + 'a, Global>
fn from(err: E) -> Box<dyn Error + 'a, Global>
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))
source§impl<'a, E> From<E> for Box<dyn Error + Sync + Send + 'a, Global>where
E: Error + Send + Sync + 'a,
Available on non-no_global_oom_handling
only.
impl<'a, E> From<E> for Box<dyn Error + Sync + Send + 'a, Global>where E: Error + Send + Sync + 'a,
no_global_oom_handling
only.source§fn from(err: E) -> Box<dyn Error + Sync + Send + 'a, Global>
fn from(err: E) -> Box<dyn Error + Sync + Send + 'a, Global>
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))
1.6.0 · source§impl From<String> for Box<dyn Error + 'static, Global>
Available on non-no_global_oom_handling
only.
impl From<String> for Box<dyn Error + 'static, Global>
no_global_oom_handling
only.source§impl From<String> for Box<dyn Error + Sync + Send + 'static, Global>
Available on non-no_global_oom_handling
only.
impl From<String> for Box<dyn Error + Sync + Send + 'static, Global>
no_global_oom_handling
only.source§fn from(err: String) -> Box<dyn Error + Sync + Send + 'static, Global>
fn from(err: String) -> Box<dyn Error + Sync + Send + 'static, Global>
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))
Implementors§
impl !Error for &str
impl Error for kvarn::encryption::Error
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
std
only.impl Error for WeightedError
std
only.impl Error for !
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 ParseIntError
impl Error for TryFromIntError
impl Error for TryFromFloatSecsError
impl Error for kvarn::prelude::fmt::Error
impl Error for InvalidHeaderName
impl Error for InvalidHeaderValue
impl Error for ToStrError
impl Error for kvarn::prelude::io::Error
impl Error for WriterPanicked
impl Error for kvarn::prelude::net::AddrParseError
impl Error for ParseBoolError
impl Error for Utf8Error
impl Error for InvalidUri
impl Error for InvalidUriParts
impl Error for KeyRejected
std
only.impl Error for Unspecified
std
only.impl Error for 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 h2::error::Error
impl Error for http::error::Error
impl Error for InvalidMethod
impl Error for InvalidStatusCode
impl Error for log::ParseLevelError
std
only.impl Error for SetLoggerError
std
only.impl Error for FromStrError
impl Error for ParseBigIntError
std
only.impl Error for uuid::error::Error
impl Error for rand::rngs::adapter::read::ReadError
impl Error for rand_core::error::Error
std
only.impl Error for Aborted
std
only.impl Error for AcquireError
impl Error for AddrParseError
std
only.Requires the std
feature.
impl Error for AnyDelimiterCodecError
impl Error for Canceled
std
only.impl Error for CapacityError
impl Error for ComponentRange
std
only.impl Error for ConfigError
impl Error for ConnectError
impl Error for ConnectionError
impl Error for ConnectionError
impl Error for ConversionRange
std
only.impl Error for DecodeError
std
only.impl Error for DecodeError
std
only.impl Error for DecodeSliceError
std
only.impl Error for DerConstraint
std
only.impl Error for DifferentVariant
std
only.impl Error for Elapsed
impl Error for EncodeSliceError
std
only.impl Error for EnterError
impl Error for Error
impl Error for Error
std
only.Requires the std
feature.
impl Error for Error
impl Error for Error
std
only.impl Error for Error
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 FinishError
impl Error for Format
std
only.impl Error for IndeterminateOffset
std
only.impl Error for InvalidBufferSize
std
only.impl Error for InvalidDnsNameError
impl Error for InvalidDnsNameError
std
only.Requires the std
feature.
impl Error for InvalidFormatDescription
std
only.impl Error for InvalidLength
std
only.impl Error for InvalidOutputSize
std
only.impl Error for InvalidVariant
std
only.impl Error for JoinError
impl Error for LengthDelimitedCodecError
impl Error for LinesCodecError
impl Error for PEMError
impl Error for Parse
std
only.impl Error for ParseAlphabetError
std
only.impl Error for ParseFromDescription
std
only.impl Error for ParseLevelError
std
only.impl Error for ParseLevelFilterError
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 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 SerializeError
impl Error for SetGlobalDefaultError
std
only.impl Error for SignError
impl Error for SpawnError
std
only.impl Error for SpecificationError
std
only.impl Error for StoppedError
impl Error for TlsError
impl Error for TryAcquireError
impl Error for TryCurrentError
impl Error for TryFromParsed
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 TrySelectError
impl Error for UnknownStream
impl Error for UnknownStream
impl Error for UrlError
impl Error for VarIntBoundsExceeded
impl Error for WriteError
impl Error for WriteError
impl Error for X509Error
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, Global>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 Twhere T: Error + ?Sized,
impl<E> Error for Err<E>where E: Debug,
std
only.impl<I> Error for Error<I>where I: Debug + Display,
std
only.impl<I> Error for VerboseError<I>where I: Debug + Display,
std
only.impl<T> Error for std::sync::mpsc::TrySendError<T>where T: Send,
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, Global>where T: Error,
impl<T> Error for ThinBox<T>where T: Error + ?Sized,
impl<T> Error for std::sync::mpsc::SendError<T>where T: Send,
impl<T> Error for PoisonError<T>
impl<T> Error for TryFromBigIntError<T>where T: Debug,
std
and has_try_from
only.impl<T> Error for PollSendError<T>where T: Debug,
impl<T> Error for ReuniteError<T>where T: Any,
std
only.impl<T> Error for SendError<T>
impl<T> Error for SendError<T>
impl<T> Error for SendError<T>where T: Send,
impl<T> Error for SendError<T>where T: Debug,
impl<T> Error for SendTimeoutError<T>
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,
std
only.impl<T, Item> Error for ReuniteError<T, Item>where T: Any,
std
only.