Trait hdk::prelude::holochain_serialized_bytes::serde::ser::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, demand: &mut Demand<'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)>

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, demand: &mut Demand<'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 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

impl<'a> dyn Error + 'a

pub fn request_ref<T>(&'a self) -> Option<&'a T>where T: 'static + ?Sized,

🔬This is a nightly-only experimental API. (error_generic_member_access)

Request a reference of type T as context about this error.

pub fn request_value<T>(&'a self) -> Option<T>where T: 'static,

🔬This is a nightly-only experimental API. (error_generic_member_access)

Request a value of type T as context about this error.

impl dyn Error + 'static

pub fn is<T>(&self) -> boolwhere 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 + 'static

pub fn is<T>(&self) -> boolwhere 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.

pub fn request_ref<T>(&self) -> Option<&T>where T: 'static + ?Sized,

🔬This is a nightly-only experimental API. (error_generic_member_access)

Request a reference of type T as context about this error.

pub fn request_value<T>(&self) -> Option<T>where T: 'static,

🔬This is a nightly-only experimental API. (error_generic_member_access)

Request a value of type T as context about this error.

impl dyn Error + Send + Sync + 'static

pub fn is<T>(&self) -> boolwhere 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.

pub fn request_ref<T>(&self) -> Option<&T>where T: 'static + ?Sized,

🔬This is a nightly-only experimental API. (error_generic_member_access)

Request a reference of type T as context about this error.

pub fn request_value<T>(&self) -> Option<T>where T: 'static,

🔬This is a nightly-only experimental API. (error_generic_member_access)

Request a value of type T as context about this error.

impl dyn Error + 'static

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 + Send + Sync + 'static

pub fn downcast<T>( self: Box<dyn Error + Send + Sync + 'static, Global> ) -> Result<Box<T, Global>, Box<dyn Error + Send + Sync + 'static, Global>>where T: Error + 'static,

Attempts to downcast the box to a concrete type.

impl dyn Error + Send + 'static

pub fn downcast<T>( self: Box<dyn Error + Send + 'static, Global> ) -> Result<Box<T, Global>, Box<dyn Error + Send + 'static, Global>>where T: Error + 'static,

Attempts to downcast the box to a concrete type.

impl dyn Error + 'static

pub fn downcast<T>( self: Box<dyn Error + 'static, Global> ) -> Result<Box<T, Global>, Box<dyn Error + 'static, Global>>where T: Error + 'static,

Attempts to downcast the box to a concrete type.

Trait Implementations

impl From<&str> for Box<dyn Error + 'static, Global>

fn from(err: &str) -> Box<dyn Error + 'static, Global>

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 + Send + Sync + 'a, Global>

fn from(err: &str) -> Box<dyn Error + Send + Sync + 'a, Global>

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> From<Cow<'a, str>> for Box<dyn Error + 'static, Global>

fn from(err: Cow<'a, str>) -> Box<dyn Error + 'static, Global>

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 + Send + Sync + 'a, Global>

fn from(err: Cow<'b, str>) -> Box<dyn Error + Send + Sync + '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))

impl<'a, E> From<E> for Box<dyn Error + 'a, Global>where E: Error + 'a,

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))

impl<'a, E> From<E> for Box<dyn Error + Send + Sync + 'a, Global>where E: Error + Send + Sync + 'a,

fn from(err: E) -> Box<dyn Error + Send + Sync + '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))

impl From<String> for Box<dyn Error + 'static, Global>

fn from(str_err: String) -> Box<dyn Error + 'static, Global>

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 From<String> for Box<dyn Error + Send + Sync + 'static, Global>

fn from(err: String) -> Box<dyn Error + Send + Sync + '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))

impl Value for dyn Error + 'static

fn record(&self, key: &Field, visitor: &mut dyn Visit)

Visits this value with the given Visitor.

impl Value for dyn Error + Send + 'static

fn record(&self, key: &Field, visitor: &mut dyn Visit)

Visits this value with the given Visitor.

impl Value for dyn Error + Send + Sync + 'static

fn record(&self, key: &Field, visitor: &mut dyn Visit)

Visits this value with the given Visitor.

impl Value for dyn Error + Sync + 'static

fn record(&self, key: &Field, visitor: &mut dyn Visit)

Visits this value with the given Visitor.

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 BernoulliError

impl Error for WeightedError

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 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 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 OutOfRangeError

impl Error for chrono::format::ParseError

impl Error for ParseWeekdayError

impl Error for getrandom::error::Error

impl Error for serde_json::error::Error

impl Error for SetGlobalDefaultError

impl Error for ParseLevelError

impl Error for ParseLevelFilterError

impl Error for ReadError

impl Error for rand_core::error::Error

impl Error for Aborted

impl Error for AllocScratchError

impl Error for AsStringError

impl Error for BinaryReaderError

impl Error for BufferSerializerError

impl Error for BytesReadError

impl Error for Canceled

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 EnterError

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 GossipError

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 SendError

impl Error for SerializeError

impl Error for SetError

impl Error for SharedDeserializeMapError

impl Error for SharedSerializeMapError

impl Error for SpawnError

impl Error for StatsError

impl Error for ThreadPoolBuildError

impl Error for TrapCode

impl Error for TryRecvError

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.

impl<S, C, H> Error for CompositeSerializerError<S, C, H>where S: Error + 'static, C: Error + 'static, H: Error + 'static,

impl<T> Error for std::sync::mpsc::TrySendError<T>where T: Send,

impl<T> Error for TryLockError<T>

impl<T> Error for Box<T, Global>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>where T: Send,

impl<T> Error for PoisonError<T>

impl<T> Error for ReuniteError<T>where T: Any,

impl<T> Error for SendError<T>where T: Send,

impl<T> Error for SendTimeoutError<T>where T: Send,

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,

impl<T, Item> Error for ReuniteError<T, Item>where T: Any,

impl<W> Error for IntoInnerError<W>where W: Send + Debug,

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