1.0.0[][src]Trait std::error::Error

pub trait Error: Debug + Display {
    fn description(&self) -> &str { ... }
fn cause(&self) -> Option<&dyn Error> { ... }
fn source(&self) -> Option<&(dyn Error + 'static)> { ... } }

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, and may provide cause chain information:

The source method 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 access to that error via the source method. This makes it possible for the high-level module to provide its own errors while also revealing some of the implementation for debugging via source chains.

Provided methods

fn description(&self) -> &str

This method is soft-deprecated.

Although using it won’t cause compilation warning, new code should use Display instead and new impls can omit it.

To obtain error description as a string, use to_string().

Examples

match "xc".parse::<u32>() {
    Err(e) => {
        // Print `e` itself, not `e.description()`.
        println!("Error: {}", e);
    }
    _ => println!("No error"),
}Run

fn cause(&self) -> Option<&dyn Error>

Deprecated since 1.33.0:

replaced by Error::source, which can support downcasting

The lower-level cause of this error, if any.

Examples

use std::error::Error;
use std::fmt;

#[derive(Debug)]
struct SuperError {
    side: 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 description(&self) -> &str {
        "I'm the superhero of errors"
    }

    fn cause(&self) -> Option<&Error> {
        Some(&self.side)
    }
}

#[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 description(&self) -> &str {
        "I'm SuperError side kick"
    }
}

fn get_super_error() -> Result<(), SuperError> {
    Err(SuperError { side: SuperErrorSideKick })
}

fn main() {
    match get_super_error() {
        Err(e) => {
            println!("Error: {}", e.description());
            println!("Caused by: {}", e.cause().unwrap());
        }
        _ => println!("No error"),
    }
}Run

fn source(&self) -> Option<&(dyn Error + 'static)>
1.30.0

The lower-level source of this error, if any.

Examples

use std::error::Error;
use std::fmt;

#[derive(Debug)]
struct SuperError {
    side: 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 description(&self) -> &str {
        "I'm the superhero of errors"
    }

    fn source(&self) -> Option<&(dyn Error + 'static)> {
        Some(&self.side)
    }
}

#[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 description(&self) -> &str {
        "I'm SuperError side kick"
    }
}

fn get_super_error() -> Result<(), SuperError> {
    Err(SuperError { side: SuperErrorSideKick })
}

fn main() {
    match get_super_error() {
        Err(e) => {
            println!("Error: {}", e.description());
            println!("Caused by: {}", e.source().unwrap());
        }
        _ => println!("No error"),
    }
}Run
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Methods

impl dyn Error + 'static[src]

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

Returns true if the boxed type is the same as T

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

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

impl dyn Error + Send + 'static[src]

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

Forwards to the method defined on the type Any.

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

Forwards to the method defined on the type Any.

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

Forwards to the method defined on the type Any.

impl dyn Error + Send + Sync + 'static[src]

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

Forwards to the method defined on the type Any.

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

Forwards to the method defined on the type Any.

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

Forwards to the method defined on the type Any.

impl dyn Error[src]

pub fn downcast<T: Error + 'static>(
    self: Box<Self>
) -> Result<Box<T>, Box<dyn Error>>
1.3.0
[src]

Attempt to downcast the box to a concrete type.

impl dyn Error + Send[src]

pub fn downcast<T: Error + 'static>(
    self: Box<Self>
) -> Result<Box<T>, Box<dyn Error + Send>>
1.3.0
[src]

Attempt to downcast the box to a concrete type.

impl dyn Error + Send + Sync[src]

pub fn downcast<T: Error + 'static>(
    self: Box<Self>
) -> Result<Box<T>, Box<Self>>
1.3.0
[src]

Attempt to downcast the box to a concrete type.

Implementations on Foreign Types

impl Error for TryFromSliceError[src]

fn cause(&self) -> Option<&dyn Error>
1.0.0
[src]

Deprecated since 1.33.0:

replaced by Error::source, which can support downcasting

fn source(&self) -> Option<&(dyn Error + 'static)>
1.30.0
[src]

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Implementors

impl Error for VarError[src]

fn cause(&self) -> Option<&dyn Error>[src]

Deprecated since 1.33.0:

replaced by Error::source, which can support downcasting

fn source(&self) -> Option<&(dyn Error + 'static)>
1.30.0
[src]

impl Error for ParseError[src]

fn cause(&self) -> Option<&dyn Error>
1.0.0
[src]

Deprecated since 1.33.0:

replaced by Error::source, which can support downcasting

fn source(&self) -> Option<&(dyn Error + 'static)>
1.30.0
[src]

impl Error for RecvTimeoutError[src]

fn source(&self) -> Option<&(dyn Error + 'static)>
1.30.0
[src]

impl Error for TryRecvError[src]

fn source(&self) -> Option<&(dyn Error + 'static)>
1.30.0
[src]

impl Error for ![src]

fn cause(&self) -> Option<&dyn Error>
1.0.0
[src]

Deprecated since 1.33.0:

replaced by Error::source, which can support downcasting

fn source(&self) -> Option<&(dyn Error + 'static)>
1.30.0
[src]

impl Error for AllocErr[src]

fn cause(&self) -> Option<&dyn Error>
1.0.0
[src]

Deprecated since 1.33.0:

replaced by Error::source, which can support downcasting

fn source(&self) -> Option<&(dyn Error + 'static)>
1.30.0
[src]

impl Error for CannotReallocInPlace[src]

fn cause(&self) -> Option<&dyn Error>
1.0.0
[src]

Deprecated since 1.33.0:

replaced by Error::source, which can support downcasting

fn source(&self) -> Option<&(dyn Error + 'static)>
1.30.0
[src]

impl Error for LayoutErr[src]

fn cause(&self) -> Option<&dyn Error>
1.0.0
[src]

Deprecated since 1.33.0:

replaced by Error::source, which can support downcasting

fn source(&self) -> Option<&(dyn Error + 'static)>
1.30.0
[src]

impl Error for BorrowError[src]

fn cause(&self) -> Option<&dyn Error>
1.0.0
[src]

Deprecated since 1.33.0:

replaced by Error::source, which can support downcasting

fn source(&self) -> Option<&(dyn Error + 'static)>
1.30.0
[src]

impl Error for BorrowMutError[src]

fn cause(&self) -> Option<&dyn Error>
1.0.0
[src]

Deprecated since 1.33.0:

replaced by Error::source, which can support downcasting

fn source(&self) -> Option<&(dyn Error + 'static)>
1.30.0
[src]

impl Error for CharTryFromError[src]

fn cause(&self) -> Option<&dyn Error>
1.0.0
[src]

Deprecated since 1.33.0:

replaced by Error::source, which can support downcasting

fn source(&self) -> Option<&(dyn Error + 'static)>
1.30.0
[src]

impl Error for DecodeUtf16Error[src]

fn cause(&self) -> Option<&dyn Error>
1.0.0
[src]

Deprecated since 1.33.0:

replaced by Error::source, which can support downcasting

fn source(&self) -> Option<&(dyn Error + 'static)>
1.30.0
[src]

impl Error for ParseCharError[src]

fn cause(&self) -> Option<&dyn Error>
1.0.0
[src]

Deprecated since 1.33.0:

replaced by Error::source, which can support downcasting

fn source(&self) -> Option<&(dyn Error + 'static)>
1.30.0
[src]

impl Error for JoinPathsError[src]

fn cause(&self) -> Option<&dyn Error>[src]

Deprecated since 1.33.0:

replaced by Error::source, which can support downcasting

fn source(&self) -> Option<&(dyn Error + 'static)>
1.30.0
[src]

impl Error for FromBytesWithNulError[src]

fn cause(&self) -> Option<&dyn Error>
1.0.0
[src]

Deprecated since 1.33.0:

replaced by Error::source, which can support downcasting

fn source(&self) -> Option<&(dyn Error + 'static)>
1.30.0
[src]

impl Error for IntoStringError[src]

fn source(&self) -> Option<&(dyn Error + 'static)>
1.30.0
[src]

impl Error for NulError[src]

fn cause(&self) -> Option<&dyn Error>[src]

Deprecated since 1.33.0:

replaced by Error::source, which can support downcasting

fn source(&self) -> Option<&(dyn Error + 'static)>
1.30.0
[src]

impl Error for std::fmt::Error[src]

fn cause(&self) -> Option<&dyn Error>
1.0.0
[src]

Deprecated since 1.33.0:

replaced by Error::source, which can support downcasting

fn source(&self) -> Option<&(dyn Error + 'static)>
1.30.0
[src]

impl Error for std::io::Error[src]

fn source(&self) -> Option<&(dyn Error + 'static)>
1.30.0
[src]

impl Error for AddrParseError[src]

fn cause(&self) -> Option<&dyn Error>
1.0.0
[src]

Deprecated since 1.33.0:

replaced by Error::source, which can support downcasting

fn source(&self) -> Option<&(dyn Error + 'static)>
1.30.0
[src]

impl Error for ParseFloatError[src]

fn cause(&self) -> Option<&dyn Error>[src]

Deprecated since 1.33.0:

replaced by Error::source, which can support downcasting

fn source(&self) -> Option<&(dyn Error + 'static)>
1.30.0
[src]

impl Error for ParseIntError[src]

fn cause(&self) -> Option<&dyn Error>[src]

Deprecated since 1.33.0:

replaced by Error::source, which can support downcasting

fn source(&self) -> Option<&(dyn Error + 'static)>
1.30.0
[src]

impl Error for TryFromIntError[src]

fn cause(&self) -> Option<&dyn Error>
1.0.0
[src]

Deprecated since 1.33.0:

replaced by Error::source, which can support downcasting

fn source(&self) -> Option<&(dyn Error + 'static)>
1.30.0
[src]

impl Error for StripPrefixError[src]

fn cause(&self) -> Option<&dyn Error>
1.0.0
[src]

Deprecated since 1.33.0:

replaced by Error::source, which can support downcasting

fn source(&self) -> Option<&(dyn Error + 'static)>
1.30.0
[src]

impl Error for ParseBoolError[src]

fn cause(&self) -> Option<&dyn Error>[src]

Deprecated since 1.33.0:

replaced by Error::source, which can support downcasting

fn source(&self) -> Option<&(dyn Error + 'static)>
1.30.0
[src]

impl Error for Utf8Error[src]

fn cause(&self) -> Option<&dyn Error>[src]

Deprecated since 1.33.0:

replaced by Error::source, which can support downcasting

fn source(&self) -> Option<&(dyn Error + 'static)>
1.30.0
[src]

impl Error for FromUtf16Error[src]

fn cause(&self) -> Option<&dyn Error>[src]

Deprecated since 1.33.0:

replaced by Error::source, which can support downcasting

fn source(&self) -> Option<&(dyn Error + 'static)>
1.30.0
[src]

impl Error for FromUtf8Error[src]

fn cause(&self) -> Option<&dyn Error>[src]

Deprecated since 1.33.0:

replaced by Error::source, which can support downcasting

fn source(&self) -> Option<&(dyn Error + 'static)>
1.30.0
[src]

impl Error for RecvError[src]

fn source(&self) -> Option<&(dyn Error + 'static)>
1.30.0
[src]

impl Error for SystemTimeError[src]

fn cause(&self) -> Option<&dyn Error>
1.0.0
[src]

Deprecated since 1.33.0:

replaced by Error::source, which can support downcasting

fn source(&self) -> Option<&(dyn Error + 'static)>
1.30.0
[src]

impl<T> Error for TryLockError<T>[src]

fn source(&self) -> Option<&(dyn Error + 'static)>
1.30.0
[src]

impl<T> Error for PoisonError<T>[src]

fn cause(&self) -> Option<&dyn Error>[src]

Deprecated since 1.33.0:

replaced by Error::source, which can support downcasting

fn source(&self) -> Option<&(dyn Error + 'static)>
1.30.0
[src]

impl<T: Error> Error for Box<T>[src]

fn source(&self) -> Option<&(dyn Error + 'static)>
1.30.0
[src]

impl<T: Send> Error for TrySendError<T>[src]

fn source(&self) -> Option<&(dyn Error + 'static)>
1.30.0
[src]

impl<T: Send> Error for SendError<T>[src]

fn source(&self) -> Option<&(dyn Error + 'static)>
1.30.0
[src]

impl<W: Send + Debug> Error for IntoInnerError<W>[src]

fn cause(&self) -> Option<&dyn Error>[src]

Deprecated since 1.33.0:

replaced by Error::source, which can support downcasting

fn source(&self) -> Option<&(dyn Error + 'static)>
1.30.0
[src]

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