1.0.0[−][src]Trait std::error::Error
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<&dyn 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
Methods
impl dyn Error + 'static[src]
pub fn is<T: Error + 'static>(&self) -> bool1.3.0[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) -> bool1.3.0[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) -> bool1.3.0[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]
self: Box<Self>
) -> Result<Box<T>, Box<dyn Error>>
Attempt to downcast the box to a concrete type.
ⓘImportant traits for ErrorIter<'a>pub fn iter_chain(&self) -> ErrorIter[src]
ⓘImportant traits for ErrorIter<'a>
Returns an iterator starting with the current error and continuing with
recursively calling source.
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.iter_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());Run
ⓘImportant traits for ErrorIter<'a>pub fn iter_sources(&self) -> ErrorIter[src]
ⓘImportant traits for ErrorIter<'a>
Returns an iterator starting with the source of this error
and continuing with recursively calling source.
Examples
#![feature(error_iter)] use std::error::Error; use std::fmt; #[derive(Debug)] struct A; #[derive(Debug)] struct B(Option<Box<dyn Error + 'static>>); #[derive(Debug)] struct C(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 fmt::Display for C { fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result { write!(f, "C") } } impl Error for A {} impl Error for B { fn source(&self) -> Option<&(dyn Error + 'static)> { self.0.as_ref().map(|e| e.as_ref()) } } impl Error for C { fn source(&self) -> Option<&(dyn Error + 'static)> { self.0.as_ref().map(|e| e.as_ref()) } } let b = B(Some(Box::new(A))); let c = C(Some(Box::new(b))); // let err : Box<Error> = c.into(); // or let err = &c as &(dyn Error); let mut iter = err.iter_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
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]
self: Box<Self>
) -> Result<Box<T>, Box<dyn Error + Send>>
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]
self: Box<Self>
) -> Result<Box<T>, Box<Self>>
Attempt to downcast the box to a concrete type.