Struct failure::Error

pub struct Error { /* fields omitted */ }

The Error type, which can contain any failure.

Functions which accumulate many kinds of errors should return this type. All failures can be converted into it, so functions which catch those errors can be tried with ? inside of a function that returns this kind of error.

In addition to implementing Debug and Display, this type carries Backtrace information, and can be downcast into the failure that underlies it for more detailed inspection.

Methods

impl Error

pub fn from_boxed_compat(err: Box<StdError + Sync + Send + 'static>) -> Error

Creates an Error from Box<std::error::Error>.

This method is useful for comparability with code, which does not use the Fail trait.

Example

use std::error::Error as StdError;
use failure::Error;

fn app_fn() -> Result<i32, Error> {
    let x = library_fn().map_err(Error::from_boxed_compat)?;
    Ok(x * 2)
}

fn library_fn() -> Result<i32, Box<StdError + Sync + Send + 'static>> {
    Ok(92)
}

pub fn as_fail(&self) -> &Fail

Return a reference to the underlying failure that this Error contains.

pub fn cause(&self) -> &Fail

Deprecated since 0.1.2

: please use 'as_fail()' method instead

Returns a reference to the underlying cause of this Error. Unlike the method on Fail, this does not return an Option. The Error type always has an underlying failure.

This method has been deprecated in favor of the [Error::as_fail] method, which does the same thing.

pub fn backtrace(&self) -> &Backtrace

Gets a reference to the Backtrace for this Error.

If the failure this wrapped carried a backtrace, that backtrace will be returned. Otherwise, the backtrace will have been constructed at the point that failure was cast into the Error type.

pub fn context<D: Display + Send + Sync + 'static>(
    self,
    context: D
) -> Context<D>

Provides context for this Error.

This can provide additional information about this error, appropriate to the semantics of the current layer. That is, if you have a lower-level error, such as an IO error, you can provide additional context about what that error means in the context of your function. This gives users of this function more information about what has gone wrong.

This takes any type that implements Display, as well as Send/Sync/'static. In practice, this means it can take a String or a string literal, or a failure, or some other custom context-carrying type.

pub fn compat(self) -> Compat<Error>

Wraps Error in a compatibility type.

This type implements the Error trait from std::error. If you need to pass failure's Error to an interface that takes any Error, you can use this method to get a compatible type.

pub fn downcast<T: Fail>(self) -> Result<T, Error>

Attempts to downcast this Error to a particular Fail type.

This downcasts by value, returning an owned T if the underlying failure is of the type T. For this reason it returns a Result - in the case that the underlying error is of a different type, the original Error is returned.

pub fn find_root_cause(&self) -> &Fail

Returns the "root cause" of this error - the last value in the cause chain which does not return an underlying cause.

Important traits for Causes<'f>

impl<'f> Iterator for Causes<'f> type Item = &'f Fail;

pub fn iter_causes(&self) -> Causes

Returns a iterator over the causes of this error with the cause of the fail as the first item and the root_cause as the final item.

Use iter_chain to also include the fail of this error itself.

Important traits for Causes<'f>

impl<'f> Iterator for Causes<'f> type Item = &'f Fail;

pub fn iter_chain(&self) -> Causes

Returns a iterator over all fails up the chain from the current as the first item up to the root_cause as the final item.

This means that the chain also includes the fail itself which means that it does not start with cause. To skip the outermost fail use iter_causes instead.

pub fn downcast_ref<T: Fail>(&self) -> Option<&T>

Attempts to downcast this Error to a particular Fail type by reference.

If the underlying error is not of type T, this will return None.

pub fn downcast_mut<T: Fail>(&mut self) -> Option<&mut T>

Attempts to downcast this Error to a particular Fail type by mutable reference.

If the underlying error is not of type T, this will return None.

pub fn root_cause(&self) -> &Fail

Deprecated since 0.1.2

: please use the 'find_root_cause()' method instead

Deprecated alias to find_root_cause.

Important traits for Causes<'f>

impl<'f> Iterator for Causes<'f> type Item = &'f Fail;

pub fn causes(&self) -> Causes

Deprecated since 0.1.2

: please use the 'iter_chain()' method instead

Deprecated alias to iter_causes.

Trait Implementations

impl From<Error> for Box<StdError>

Important traits for Box<R>

impl<R> Read for Box<R> where
    R: Read + ?Sized, impl<W> Write for Box<W> where
    W: Write + ?Sized, impl<I> Iterator for Box<I> where
    I: Iterator + ?Sized,  type Item = <I as Iterator>::Item;

fn from(error: Error) -> Box<StdError>

Performs the conversion.

impl<T> ResultExt<T, Error> for Result<T, Error>

fn compat(self) -> Result<T, Compat<Error>>

Wraps the error in Compat to make it compatible with older error handling APIs that expect std::error::Error.

fn context<D>(self, context: D) -> Result<T, Context<D>> where
    D: Display + Send + Sync + 'static, 

Wraps the error type in a context type.

fn with_context<F, D>(self, f: F) -> Result<T, Context<D>> where
    F: FnOnce(&Error) -> D,
    D: Display + Send + Sync + 'static, 

Wraps the error type in a context type generated by looking at the error value.

impl<F: Fail> From<F> for Error

fn from(failure: F) -> Error

Performs the conversion.

impl Display for Error

fn fmt(&self, f: &mut Formatter) -> Result

Formats the value using the given formatter.

impl Debug for Error

fn fmt(&self, f: &mut Formatter) -> Result

Formats the value using the given formatter.

impl AsRef<Fail> for Error

fn as_ref(&self) -> &Fail

Performs the conversion.