1.0.0[−][src]Trait std::error::Error

pub trait Error: Debug + Display {
    fn description(&self) -> &str { ... }
    fn cause(&self) -> Option<&Error> { ... }
    fn source(&self) -> Option<&(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 cause method is generally used when errors cross "abstraction boundaries", i.e. when a one module must report an error that is "caused" by an error from a lower-level module. This setup makes it possible for the high-level module to provide its own errors that do not commit to any particular implementation, but also reveal some of its implementation for debugging via cause 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<&Error>`

Deprecating in 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<&(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

Methods

`impl 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.