Struct argmin::core::Error[][src]

#[repr(transparent)]
pub struct Error { /* fields omitted */ }

The Error type, a wrapper around a dynamic error type.

Error works a lot like Box<dyn std::error::Error>, but with these differences:


Display representations

When you print an error object using “{}” or to_string(), only the outermost underlying error or context is printed, not any of the lower level causes. This is exactly as if you had called the Display impl of the error from which you constructed your anyhow::Error.

Failed to read instrs from ./path/to/instrs.json

To print causes as well using anyhow’s default formatting of causes, use the alternate selector “{:#}”.

Failed to read instrs from ./path/to/instrs.json: No such file or directory (os error 2)

The Debug format “{:?}” includes your backtrace if one was captured. Note that this is the representation you get by default if you return an error from fn main instead of printing it explicitly yourself.

Error: Failed to read instrs from ./path/to/instrs.json

Caused by:
    No such file or directory (os error 2)

and if there is a backtrace available:

Error: Failed to read instrs from ./path/to/instrs.json

Caused by:
    No such file or directory (os error 2)

Stack backtrace:
   0: <E as anyhow::context::ext::StdError>::ext_context
             at /git/anyhow/src/backtrace.rs:26
   1: core::result::Result<T,E>::map_err
             at /git/rustc/src/libcore/result.rs:596
   2: anyhow::context::<impl anyhow::Context<T,E> for core::result::Result<T,E>>::with_context
             at /git/anyhow/src/context.rs:58
   3: testing::main
             at src/main.rs:5
   4: std::rt::lang_start
             at /git/rustc/src/libstd/rt.rs:61
   5: main
   6: __libc_start_main
   7: _start

To see a conventional struct-style Debug representation, use “{:#?}”.

Error {
    context: "Failed to read instrs from ./path/to/instrs.json",
    source: Os {
        code: 2,
        kind: NotFound,
        message: "No such file or directory",
    },
}

If none of the built-in representations are appropriate and you would prefer to render the error and its cause chain yourself, it can be done something like this:

use anyhow::{Context, Result};

fn main() {
    if let Err(err) = try_main() {
        eprintln!("ERROR: {}", err);
        err.chain().skip(1).for_each(|cause| eprintln!("because: {}", cause));
        std::process::exit(1);
    }
}

fn try_main() -> Result<()> {
    ...
}

Implementations

impl Error[src]

pub fn new<E>(error: E) -> Error where
    E: Error + Send + Sync + 'static, 
[src]

Create a new error object from any error type.

The error type must be threadsafe and 'static, so that the Error will be as well.

If the error type does not provide a backtrace, a backtrace will be created here to ensure that a backtrace exists.

pub fn msg<M>(message: M) -> Error where
    M: Display + Debug + Send + Sync + 'static, 
[src]

Create a new error object from a printable error message.

If the argument implements std::error::Error, prefer Error::new instead which preserves the underlying error’s cause chain and backtrace. If the argument may or may not implement std::error::Error now or in the future, use anyhow!(err) which handles either way correctly.

Error::msg("...") is equivalent to anyhow!("...") but occasionally convenient in places where a function is preferable over a macro, such as iterator or stream combinators:

use anyhow::{Error, Result};
use futures::stream::{Stream, StreamExt, TryStreamExt};

async fn demo<S>(stream: S) -> Result<Vec<Output>>
where
    S: Stream<Item = Input>,
{
    stream
        .then(ffi::do_some_work) // returns Result<Output, &str>
        .map_err(Error::msg)
        .try_collect()
        .await
}

pub fn context<C>(self, context: C) -> Error where
    C: Display + Send + Sync + 'static, 
[src]

Wrap the error value with additional context.

For attaching context to a Result as it is propagated, the Context extension trait may be more convenient than this function.

The primary reason to use error.context(...) instead of result.context(...) via the Context trait would be if the context needs to depend on some data held by the underlying error:

use anyhow::Result;
use std::fs::File;
use std::path::Path;

struct ParseError {
    line: usize,
    column: usize,
}

fn parse_impl(file: File) -> Result<T, ParseError> {
    ...
}

pub fn parse(path: impl AsRef<Path>) -> Result<T> {
    let file = File::open(&path)?;
    parse_impl(file).map_err(|error| {
        let context = format!(
            "only the first {} lines of {} are valid",
            error.line, path.as_ref().display(),
        );
        anyhow::Error::new(error).context(context)
    })
}

pub fn chain(&self) -> Chain<'_>[src]

An iterator of the chain of source errors contained by this Error.

This iterator will visit every error in the cause chain of this error object, beginning with the error that this error object was created from.

Example

use anyhow::Error;
use std::io;

pub fn underlying_io_error_kind(error: &Error) -> Option<io::ErrorKind> {
    for cause in error.chain() {
        if let Some(io_error) = cause.downcast_ref::<io::Error>() {
            return Some(io_error.kind());
        }
    }
    None
}

pub fn root_cause(&self) -> &(dyn Error + 'static)[src]

The lowest level cause of this error — this error’s cause’s cause’s cause etc.

The root cause is the last error in the iterator produced by chain().

pub fn is<E>(&self) -> bool where
    E: Display + Debug + Send + Sync + 'static, 
[src]

Returns true if E is the type held by this error object.

For errors with context, this method returns true if E matches the type of the context C or the type of the error on which the context has been attached. For details about the interaction between context and downcasting, see here.

pub fn downcast<E>(self) -> Result<E, Error> where
    E: Display + Debug + Send + Sync + 'static, 
[src]

Attempt to downcast the error object to a concrete type.

pub fn downcast_ref<E>(&self) -> Option<&E> where
    E: Display + Debug + Send + Sync + 'static, 
[src]

Downcast this error object by reference.

Example

// If the error was caused by redaction, then return a tombstone instead
// of the content.
match root_cause.downcast_ref::<DataStoreError>() {
    Some(DataStoreError::Censored(_)) => Ok(Poll::Ready(REDACTED_CONTENT)),
    None => Err(error),
}

pub fn downcast_mut<E>(&mut self) -> Option<&mut E> where
    E: Display + Debug + Send + Sync + 'static, 
[src]

Downcast this error object by mutable reference.

Methods from Deref<Target = dyn Error + 'static + Send + Sync>

pub fn is<T>(&self) -> bool where
    T: 'static + Error
1.3.0[src]

Returns true if the boxed type is the same as T

pub fn downcast_ref<T>(&self) -> Option<&T> where
    T: 'static + Error
1.3.0[src]

Returns some reference to the boxed 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: 'static + Error
1.3.0[src]

Returns some mutable reference to the boxed value if it is of type T, or None if it isn’t.

pub fn is<T>(&self) -> bool where
    T: 'static + Error
1.3.0[src]

Forwards to the method defined on the type dyn Error.

pub fn downcast_ref<T>(&self) -> Option<&T> where
    T: 'static + Error
1.3.0[src]

Forwards to the method defined on the type dyn Error.

pub fn downcast_mut<T>(&mut self) -> Option<&mut T> where
    T: 'static + Error
1.3.0[src]

Forwards to the method defined on the type dyn Error.

pub fn is<T>(&self) -> bool where
    T: 'static + Error
1.3.0[src]

Forwards to the method defined on the type dyn Error.

pub fn downcast_ref<T>(&self) -> Option<&T> where
    T: 'static + Error
1.3.0[src]

Forwards to the method defined on the type dyn Error.

pub fn downcast_mut<T>(&mut self) -> Option<&mut T> where
    T: 'static + Error
1.3.0[src]

Forwards to the method defined on the type dyn Error.

pub fn chain(&self) -> Chain<'_>[src]

🔬 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.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

impl AsRef<dyn Error + 'static + Send + Sync> for Error[src]

impl AsRef<dyn Error + 'static> for Error[src]

impl Debug for Error[src]

impl Deref for Error[src]

type Target = dyn Error + 'static + Send + Sync

The resulting type after dereferencing.

impl DerefMut for Error[src]

impl Display for Error[src]

impl Drop for Error[src]

impl<E> From<E> for Error where
    E: Error + Send + Sync + 'static, 
[src]

Auto Trait Implementations

impl RefUnwindSafe for Error

impl Send for Error

impl Sync for Error

impl Unpin for Error

impl UnwindSafe for Error

Blanket Implementations

impl<T> Any for T where
    T: 'static + ?Sized
[src]

impl<T> Borrow<T> for T where
    T: ?Sized
[src]

impl<T> BorrowMut<T> for T where
    T: ?Sized
[src]

impl<T> From<!> for T[src]

impl<T> From<T> for T[src]

impl<T, U> Into<U> for T where
    U: From<T>, 
[src]

impl<T> Same<T> for T

type Output = T

Should always be Self

impl<SS, SP> SupersetOf<SS> for SP where
    SS: SubsetOf<SP>, 

impl<T> ToString for T where
    T: Display + ?Sized
[src]

impl<T, U> TryFrom<U> for T where
    U: Into<T>, 
[src]

type Error = Infallible

The type returned in the event of a conversion error.

impl<T, U> TryInto<U> for T where
    U: TryFrom<T>, 
[src]

type Error = <U as TryFrom<T>>::Error

The type returned in the event of a conversion error.

impl<V, T> VZip<V> for T where
    V: MultiLane<T>, 

impl<T> SendSyncUnwindSafe for T where
    T: Send + Sync + UnwindSafe + ?Sized