pub trait StdError: Debug + Display {
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>) { ... }
}
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: 'static + Error,
pub fn is<T>(&self) -> boolwhere
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.
source§impl dyn Error + Send + 'static
impl dyn Error + Send + 'static
1.3.0 · sourcepub fn is<T>(&self) -> boolwhere
T: 'static + Error,
pub fn is<T>(&self) -> boolwhere
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
.
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: 'static + Error,
pub fn is<T>(&self) -> boolwhere
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
.
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>
impl From<&str> for Box<dyn Error + 'static, Global>
source§impl<'a> From<&str> for Box<dyn Error + Sync + Send + 'a, Global>
impl<'a> From<&str> for Box<dyn Error + Sync + Send + 'a, Global>
1.22.0 · source§impl<'a> From<Cow<'a, str>> for Box<dyn Error + 'static, Global>
impl<'a> From<Cow<'a, str>> for Box<dyn Error + 'static, Global>
1.22.0 · source§impl<'a, 'b> From<Cow<'b, str>> for Box<dyn Error + Sync + Send + 'a, Global>
impl<'a, 'b> From<Cow<'b, str>> for Box<dyn Error + Sync + Send + 'a, Global>
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: 'a + Error,
impl<'a, E> From<E> for Box<dyn Error + 'a, Global>where
E: 'a + Error,
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: 'a + Error + Send + Sync,
impl<'a, E> From<E> for Box<dyn Error + Sync + Send + 'a, Global>where
E: 'a + Error + Send + Sync,
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>
impl From<String> for Box<dyn Error + 'static, Global>
source§impl From<String> for Box<dyn Error + Sync + Send + 'static, Global>
impl From<String> for Box<dyn Error + Sync + Send + 'static, Global>
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 CounterSigningError
impl Error for EntryError
impl Error for SecurePrimitiveError
impl Error for ActionError
impl Error for CloneIdError
impl Error for HostFnApiError
impl Error for ScheduleError
impl Error for TimestampError
impl Error for ZomeError
impl Error for SerializedBytesError
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 time::ParseError
impl Error for RoundingError
impl Error for HoloHashError
impl Error for !
impl Error for hdk::prelude::WasmError
impl Error for WrongActionError
impl Error for hdk::prelude::holochain_serialized_bytes::serde::de::value::Error
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 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 ParseFloatError
impl Error for ParseIntError
impl Error for TryFromIntError
impl Error for ParseBoolError
impl Error for Utf8Error
impl Error for TryFromFloatSecsError
impl Error for JoinPathsError
impl Error for WriterPanicked
impl Error for std::io::error::Error
impl Error for AddrParseError
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 OutOfRangeError
impl Error for chrono::format::ParseError
impl Error for ParseWeekdayError
impl Error for serde_json::error::Error
impl Error for SetGlobalDefaultError
impl Error for ParseLevelError
impl Error for ParseLevelFilterError
impl Error for AllocScratchError
impl Error for AsStringError
impl Error for BinaryReaderError
impl Error for BufferSerializerError
impl Error for BytesReadError
impl Error for CodegenError
impl Error for CompileError
impl Error for ConvertError
impl Error for DataValueCastFailure
impl Error for DecodeError
impl Error for DeserializeError
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 ExportError
impl Error for FixedSizeScratchError
impl Error for GetTimezoneError
impl Error for GlobalError
impl Error for HostEnvInitError
impl Error for ImportError
impl Error for InstantiationError
impl Error for InstantiationError
impl Error for LinkError
impl Error for LockError
impl Error for LookupError
impl Error for MemoryError
impl Error for MiddlewareError
impl Error for NumValueReadError<Error>
impl Error for OffsetError
impl Error for PageCountOutOfRange
impl Error for ParseCpuFeatureError
impl Error for PreInstantiationError
impl Error for RecvError
impl Error for RecvTimeoutError
impl Error for RegisterMappingError
impl Error for RuntimeError
impl Error for SelectTimeoutError
impl Error for SerializeError
impl Error for SetError
impl Error for ThreadPoolBuildError
impl Error for TrapCode
impl Error for TryRecvError
impl Error for TrySelectError
impl Error for UnixTimestampError
impl Error for ValueReadError<Error>
impl Error for VerifierError
impl Error for VerifierErrors
impl Error for WasmError
impl<'a, E> Error for DecodeStringError<'a, E>where
E: RmpReadErr,
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 ValueWriteError<E>where
E: RmpWriteErr,
impl<L, R> Error for Either<L, R>where
L: Error,
R: Error,
Either
implements Error
if both L
and R
implement it.