Trait std::error::Error

1.0.0 · source ·
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, request: &mut Request<'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");
Run

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 · source

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"),
    }
}
Run
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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}");
}
Run
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fn cause(&self) -> Option<&dyn Error>

👎Deprecated since 1.33.0: replaced by Error::source, which can support downcasting
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fn provide<'a>(&'a self, request: &mut Request<'a>)

🔬This is a nightly-only experimental API. (error_generic_member_access #99301)

Provides type based access to context intended for error reports.

Used in conjunction with Request::provide_value and Request::provide_ref to extract references to member variables from dyn Error trait objects.

§Example
#![feature(error_generic_member_access)]
#![feature(error_in_core)]
use core::fmt;
use core::error::{request_ref, Request};

#[derive(Debug)]
enum MyLittleTeaPot {
    Empty,
}

#[derive(Debug)]
struct MyBacktrace {
    // ...
}

impl MyBacktrace {
    fn new() -> MyBacktrace {
        // ...
    }
}

#[derive(Debug)]
struct Error {
    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, request: &mut Request<'a>) {
        request
            .provide_ref::<MyBacktrace>(&self.backtrace);
    }
}

fn main() {
    let backtrace = MyBacktrace::new();
    let error = Error { backtrace };
    let dyn_error = &error as &dyn std::error::Error;
    let backtrace_ref = request_ref::<MyBacktrace>(dyn_error).unwrap();

    assert!(core::ptr::eq(&error.backtrace, backtrace_ref));
    assert!(request_ref::<MyLittleTeaPot>(dyn_error).is_none());
}
Run

Implementations§

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impl dyn Error

1.3.0 · source

pub fn is<T>(&self) -> bool
where T: Error + 'static,

Returns true if the inner type is the same as T.

1.3.0 · source

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 · source

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.

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impl dyn Error + Send

1.3.0 · source

pub fn is<T>(&self) -> bool
where T: Error + 'static,

Forwards to the method defined on the type dyn Error.

1.3.0 · source

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 · source

pub fn downcast_mut<T>(&mut self) -> Option<&mut T>
where T: Error + 'static,

Forwards to the method defined on the type dyn Error.

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impl dyn Error + Sync + Send

1.3.0 · source

pub fn is<T>(&self) -> bool
where T: Error + 'static,

Forwards to the method defined on the type dyn Error.

1.3.0 · source

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 · source

pub fn downcast_mut<T>(&mut self) -> Option<&mut T>
where T: Error + 'static,

Forwards to the method defined on the type dyn Error.

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impl dyn Error

source

pub fn sources(&self) -> Source<'_>

🔬This is a nightly-only experimental API. (error_iter #58520)

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());
Run
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impl dyn Error + Sync + Send

1.3.0 · source

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

Attempts to downcast the box to a concrete type.

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impl dyn Error + Send

1.3.0 · source

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

Attempts to downcast the box to a concrete type.

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impl dyn Error

1.3.0 · source

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

Attempts to downcast the box to a concrete type.

Trait Implementations§

1.6.0 · source§

impl From<&str> for Box<dyn Error>

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fn from(err: &str) -> Box<dyn Error>

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))
Run
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impl<'a> From<&str> for Box<dyn Error + Sync + Send + 'a>

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

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))
Run
1.22.0 · source§

impl<'a> From<Cow<'a, str>> for Box<dyn Error>

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

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))
Run
1.22.0 · source§

impl<'a, 'b> From<Cow<'b, str>> for Box<dyn Error + Sync + Send + 'a>

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

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

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

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

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

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))
Run
1.6.0 · source§

impl From<String> for Box<dyn Error>

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fn from(str_err: String) -> Box<dyn Error>

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))
Run
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impl From<String> for Box<dyn Error + Sync + Send>

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

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))
Run

Implementors§

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impl !Error for &str

1.8.0 · source§

impl Error for Infallible

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impl Error for VarError

1.15.0 · source§

impl Error for RecvTimeoutError

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impl Error for TryRecvError

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impl Error for !

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impl Error for AllocError

1.28.0 · source§

impl Error for LayoutError

1.34.0 · source§

impl Error for TryFromSliceError

1.13.0 · source§

impl Error for BorrowError

1.13.0 · source§

impl Error for BorrowMutError

1.34.0 · source§

impl Error for CharTryFromError

1.9.0 · source§

impl Error for DecodeUtf16Error

1.20.0 · source§

impl Error for ParseCharError

1.59.0 · source§

impl Error for TryFromCharError

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impl Error for UnorderedKeyError

1.57.0 · source§

impl Error for TryReserveError

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impl Error for JoinPathsError

1.69.0 · source§

impl Error for FromBytesUntilNulError

1.17.0 · source§

impl Error for FromBytesWithNulError

1.58.0 · source§

impl Error for FromVecWithNulError

1.7.0 · source§

impl Error for IntoStringError

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impl Error for NulError

1.11.0 · source§

impl Error for std::fmt::Error

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impl Error for std::io::Error

1.56.0 · source§

impl Error for WriterPanicked

1.4.0 · source§

impl Error for AddrParseError

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impl Error for ParseFloatError

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impl Error for ParseIntError

1.34.0 · source§

impl Error for TryFromIntError

1.63.0 · source§

impl Error for InvalidHandleError

Available on Windows only.
1.63.0 · source§

impl Error for NullHandleError

Available on Windows only.
1.7.0 · source§

impl Error for StripPrefixError

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impl Error for ExitStatusError

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impl Error for ParseBoolError

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impl Error for Utf8Error

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impl Error for FromUtf8Error

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impl Error for FromUtf16Error

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impl Error for RecvError

1.26.0 · source§

impl Error for AccessError

1.8.0 · source§

impl Error for SystemTimeError

1.66.0 · source§

impl Error for TryFromFloatSecsError

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impl<'a, K, V> Error for std::collections::btree_map::OccupiedError<'a, K, V>
where K: Debug + Ord, V: Debug,

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impl<'a, K: Debug, V: Debug> Error for std::collections::hash_map::OccupiedError<'a, K, V>

1.51.0 · source§

impl<'a, T> Error for &'a T
where T: Error + ?Sized,

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impl<T> Error for TryLockError<T>

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impl<T> Error for TrySendError<T>

1.8.0 · source§

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

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impl<T> Error for ThinBox<T>
where T: Error + ?Sized,

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impl<T> Error for SendError<T>

1.52.0 · source§

impl<T> Error for Arc<T>
where T: Error + ?Sized,

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impl<T> Error for PoisonError<T>

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

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