| //! Traits for working with Errors. |
| |
| #![stable(feature = "rust1", since = "1.0.0")] |
| |
| // A note about crates and the facade: |
| // |
| // Originally, the `Error` trait was defined in libcore, and the impls |
| // were scattered about. However, coherence objected to this |
| // arrangement, because to create the blanket impls for `Box` required |
| // knowing that `&str: !Error`, and we have no means to deal with that |
| // sort of conflict just now. Therefore, for the time being, we have |
| // moved the `Error` trait into libstd. As we evolve a sol'n to the |
| // coherence challenge (e.g., specialization, neg impls, etc) we can |
| // reconsider what crate these items belong in. |
| |
| use core::array; |
| |
| use crate::alloc::{AllocErr, LayoutErr, CannotReallocInPlace}; |
| use crate::any::TypeId; |
| use crate::borrow::Cow; |
| use crate::cell; |
| use crate::char; |
| use crate::fmt::{self, Debug, Display}; |
| use crate::mem::transmute; |
| use crate::num; |
| use crate::str; |
| use crate::string; |
| |
| /// `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. |
| /// |
| /// [`Result<T, E>`]: ../result/enum.Result.html |
| /// [`Display`]: ../fmt/trait.Display.html |
| /// [`Debug`]: ../fmt/trait.Debug.html |
| /// [`source`]: trait.Error.html#method.source |
| #[stable(feature = "rust1", since = "1.0.0")] |
| pub trait Error: Debug + Display { |
| /// **This method is soft-deprecated.** |
| /// |
| /// Although using it won’t cause compilation warning, |
| /// new code should use [`Display`] instead |
| /// and new `impl`s can omit it. |
| /// |
| /// To obtain error description as a string, use `to_string()`. |
| /// |
| /// [`Display`]: ../fmt/trait.Display.html |
| /// |
| /// # Examples |
| /// |
| /// ``` |
| /// match "xc".parse::<u32>() { |
| /// Err(e) => { |
| /// // Print `e` itself, not `e.description()`. |
| /// println!("Error: {}", e); |
| /// } |
| /// _ => println!("No error"), |
| /// } |
| /// ``` |
| #[stable(feature = "rust1", since = "1.0.0")] |
| fn description(&self) -> &str { |
| "description() is deprecated; use Display" |
| } |
| |
| /// 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"), |
| /// } |
| /// } |
| /// ``` |
| #[stable(feature = "rust1", since = "1.0.0")] |
| #[rustc_deprecated(since = "1.33.0", reason = "replaced by Error::source, which can support \ |
| downcasting")] |
| fn cause(&self) -> Option<&dyn Error> { |
| self.source() |
| } |
| |
| /// 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"), |
| /// } |
| /// } |
| /// ``` |
| #[stable(feature = "error_source", since = "1.30.0")] |
| fn source(&self) -> Option<&(dyn Error + 'static)> { None } |
| |
| /// Gets the `TypeId` of `self` |
| #[doc(hidden)] |
| #[unstable(feature = "error_type_id", |
| reason = "this is memory unsafe to override in user code", |
| issue = "60784")] |
| fn type_id(&self) -> TypeId where Self: 'static { |
| TypeId::of::<Self>() |
| } |
| } |
| |
| #[stable(feature = "rust1", since = "1.0.0")] |
| impl<'a, E: Error + 'a> From<E> for Box<dyn Error + 'a> { |
| /// Converts a type of [`Error`] into a box of dyn [`Error`]. |
| /// |
| /// # Examples |
| /// |
| /// ``` |
| /// use std::error::Error; |
| /// use std::fmt; |
| /// use std::mem; |
| /// |
| /// #[derive(Debug)] |
| /// struct AnError; |
| /// |
| /// impl fmt::Display for AnError { |
| /// fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result { |
| /// write!(f , "An error") |
| /// } |
| /// } |
| /// |
| /// impl Error for AnError { |
| /// fn description(&self) -> &str { |
| /// "Description of an error" |
| /// } |
| /// } |
| /// |
| /// let an_error = AnError; |
| /// assert!(0 == mem::size_of_val(&an_error)); |
| /// let a_boxed_error = Box::<Error>::from(an_error); |
| /// assert!(mem::size_of::<Box<dyn Error>>() == mem::size_of_val(&a_boxed_error)) |
| /// ``` |
| fn from(err: E) -> Box<dyn Error + 'a> { |
| Box::new(err) |
| } |
| } |
| |
| #[stable(feature = "rust1", since = "1.0.0")] |
| impl<'a, E: Error + Send + Sync + 'a> From<E> for Box<dyn Error + Send + Sync + 'a> { |
| /// Converts a type of [`Error`] + [`Send`] + [`Sync`] into a box of dyn [`Error`] + |
| /// [`Send`] + [`Sync`]. |
| /// |
| /// # Examples |
| /// |
| /// ``` |
| /// use std::error::Error; |
| /// use std::fmt; |
| /// use std::mem; |
| /// |
| /// #[derive(Debug)] |
| /// struct AnError; |
| /// |
| /// impl fmt::Display for AnError { |
| /// fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result { |
| /// write!(f , "An error") |
| /// } |
| /// } |
| /// |
| /// impl Error for AnError { |
| /// fn description(&self) -> &str { |
| /// "Description of an error" |
| /// } |
| /// } |
| /// |
| /// unsafe impl Send for AnError {} |
| /// |
| /// unsafe impl Sync for AnError {} |
| /// |
| /// let an_error = AnError; |
| /// assert!(0 == mem::size_of_val(&an_error)); |
| /// let a_boxed_error = Box::<Error + Send + Sync>::from(an_error); |
| /// assert!( |
| /// mem::size_of::<Box<dyn Error + Send + Sync>>() == mem::size_of_val(&a_boxed_error)) |
| /// ``` |
| fn from(err: E) -> Box<dyn Error + Send + Sync + 'a> { |
| Box::new(err) |
| } |
| } |
| |
| #[stable(feature = "rust1", since = "1.0.0")] |
| impl From<String> for Box<dyn Error + Send + Sync> { |
| /// Converts a [`String`] into a box of dyn [`Error`] + [`Send`] + [`Sync`]. |
| /// |
| /// # Examples |
| /// |
| /// ``` |
| /// use std::error::Error; |
| /// use std::mem; |
| /// |
| /// let a_string_error = "a string error".to_string(); |
| /// let a_boxed_error = Box::<Error + Send + Sync>::from(a_string_error); |
| /// assert!( |
| /// mem::size_of::<Box<dyn Error + Send + Sync>>() == mem::size_of_val(&a_boxed_error)) |
| /// ``` |
| fn from(err: String) -> Box<dyn Error + Send + Sync> { |
| #[derive(Debug)] |
| struct StringError(String); |
| |
| impl Error for StringError { |
| fn description(&self) -> &str { &self.0 } |
| } |
| |
| impl Display for StringError { |
| fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result { |
| Display::fmt(&self.0, f) |
| } |
| } |
| |
| Box::new(StringError(err)) |
| } |
| } |
| |
| #[stable(feature = "string_box_error", since = "1.6.0")] |
| impl From<String> for Box<dyn Error> { |
| /// Converts a [`String`] into a box of dyn [`Error`]. |
| /// |
| /// # Examples |
| /// |
| /// ``` |
| /// use std::error::Error; |
| /// use std::mem; |
| /// |
| /// let a_string_error = "a string error".to_string(); |
| /// let a_boxed_error = Box::<Error>::from(a_string_error); |
| /// assert!(mem::size_of::<Box<dyn Error>>() == mem::size_of_val(&a_boxed_error)) |
| /// ``` |
| fn from(str_err: String) -> Box<dyn Error> { |
| let err1: Box<dyn Error + Send + Sync> = From::from(str_err); |
| let err2: Box<dyn Error> = err1; |
| err2 |
| } |
| } |
| |
| #[stable(feature = "rust1", since = "1.0.0")] |
| impl<'a> From<&str> for Box<dyn Error + Send + Sync + 'a> { |
| /// Converts a [`str`] into a box of dyn [`Error`] + [`Send`] + [`Sync`]. |
| /// |
| /// # Examples |
| /// |
| /// ``` |
| /// use std::error::Error; |
| /// use std::mem; |
| /// |
| /// let a_str_error = "a str error"; |
| /// let a_boxed_error = Box::<Error + Send + Sync>::from(a_str_error); |
| /// assert!( |
| /// mem::size_of::<Box<dyn Error + Send + Sync>>() == mem::size_of_val(&a_boxed_error)) |
| /// ``` |
| fn from(err: &str) -> Box<dyn Error + Send + Sync + 'a> { |
| From::from(String::from(err)) |
| } |
| } |
| |
| #[stable(feature = "string_box_error", since = "1.6.0")] |
| impl From<&str> for Box<dyn Error> { |
| /// Converts a [`str`] into a box of dyn [`Error`]. |
| /// |
| /// # Examples |
| /// |
| /// ``` |
| /// use std::error::Error; |
| /// use std::mem; |
| /// |
| /// let a_str_error = "a str error"; |
| /// let a_boxed_error = Box::<Error>::from(a_str_error); |
| /// assert!(mem::size_of::<Box<dyn Error>>() == mem::size_of_val(&a_boxed_error)) |
| /// ``` |
| fn from(err: &str) -> Box<dyn Error> { |
| From::from(String::from(err)) |
| } |
| } |
| |
| #[stable(feature = "cow_box_error", since = "1.22.0")] |
| impl<'a, 'b> From<Cow<'b, str>> for Box<dyn Error + Send + Sync + 'a> { |
| /// Converts a [`Cow`] into a box of dyn [`Error`] + [`Send`] + [`Sync`]. |
| /// |
| /// # Examples |
| /// |
| /// ``` |
| /// use std::error::Error; |
| /// use std::mem; |
| /// use std::borrow::Cow; |
| /// |
| /// let a_cow_str_error = Cow::from("a str error"); |
| /// let a_boxed_error = Box::<Error + Send + Sync>::from(a_cow_str_error); |
| /// assert!( |
| /// mem::size_of::<Box<dyn Error + Send + Sync>>() == mem::size_of_val(&a_boxed_error)) |
| /// ``` |
| fn from(err: Cow<'b, str>) -> Box<dyn Error + Send + Sync + 'a> { |
| From::from(String::from(err)) |
| } |
| } |
| |
| #[stable(feature = "cow_box_error", since = "1.22.0")] |
| impl<'a> From<Cow<'a, str>> for Box<dyn Error> { |
| /// Converts a [`Cow`] into a box of dyn [`Error`]. |
| /// |
| /// # Examples |
| /// |
| /// ``` |
| /// use std::error::Error; |
| /// use std::mem; |
| /// use std::borrow::Cow; |
| /// |
| /// let a_cow_str_error = Cow::from("a str error"); |
| /// let a_boxed_error = Box::<Error>::from(a_cow_str_error); |
| /// assert!(mem::size_of::<Box<dyn Error>>() == mem::size_of_val(&a_boxed_error)) |
| /// ``` |
| fn from(err: Cow<'a, str>) -> Box<dyn Error> { |
| From::from(String::from(err)) |
| } |
| } |
| |
| #[unstable(feature = "never_type", issue = "35121")] |
| impl Error for ! { |
| fn description(&self) -> &str { *self } |
| } |
| |
| #[unstable(feature = "allocator_api", |
| reason = "the precise API and guarantees it provides may be tweaked.", |
| issue = "32838")] |
| impl Error for AllocErr { |
| fn description(&self) -> &str { |
| "memory allocation failed" |
| } |
| } |
| |
| #[unstable(feature = "allocator_api", |
| reason = "the precise API and guarantees it provides may be tweaked.", |
| issue = "32838")] |
| impl Error for LayoutErr { |
| fn description(&self) -> &str { |
| "invalid parameters to Layout::from_size_align" |
| } |
| } |
| |
| #[unstable(feature = "allocator_api", |
| reason = "the precise API and guarantees it provides may be tweaked.", |
| issue = "32838")] |
| impl Error for CannotReallocInPlace { |
| fn description(&self) -> &str { |
| CannotReallocInPlace::description(self) |
| } |
| } |
| |
| #[stable(feature = "rust1", since = "1.0.0")] |
| impl Error for str::ParseBoolError { |
| fn description(&self) -> &str { "failed to parse bool" } |
| } |
| |
| #[stable(feature = "rust1", since = "1.0.0")] |
| impl Error for str::Utf8Error { |
| fn description(&self) -> &str { |
| "invalid utf-8: corrupt contents" |
| } |
| } |
| |
| #[stable(feature = "rust1", since = "1.0.0")] |
| impl Error for num::ParseIntError { |
| fn description(&self) -> &str { |
| self.__description() |
| } |
| } |
| |
| #[stable(feature = "try_from", since = "1.34.0")] |
| impl Error for num::TryFromIntError { |
| fn description(&self) -> &str { |
| self.__description() |
| } |
| } |
| |
| #[stable(feature = "try_from", since = "1.34.0")] |
| impl Error for array::TryFromSliceError { |
| fn description(&self) -> &str { |
| self.__description() |
| } |
| } |
| |
| #[stable(feature = "rust1", since = "1.0.0")] |
| impl Error for num::ParseFloatError { |
| fn description(&self) -> &str { |
| self.__description() |
| } |
| } |
| |
| #[stable(feature = "rust1", since = "1.0.0")] |
| impl Error for string::FromUtf8Error { |
| fn description(&self) -> &str { |
| "invalid utf-8" |
| } |
| } |
| |
| #[stable(feature = "rust1", since = "1.0.0")] |
| impl Error for string::FromUtf16Error { |
| fn description(&self) -> &str { |
| "invalid utf-16" |
| } |
| } |
| |
| #[stable(feature = "str_parse_error2", since = "1.8.0")] |
| impl Error for string::ParseError { |
| fn description(&self) -> &str { |
| match *self {} |
| } |
| } |
| |
| #[stable(feature = "decode_utf16", since = "1.9.0")] |
| impl Error for char::DecodeUtf16Error { |
| fn description(&self) -> &str { |
| "unpaired surrogate found" |
| } |
| } |
| |
| #[stable(feature = "box_error", since = "1.8.0")] |
| impl<T: Error> Error for Box<T> { |
| fn description(&self) -> &str { |
| Error::description(&**self) |
| } |
| |
| #[allow(deprecated)] |
| fn cause(&self) -> Option<&dyn Error> { |
| Error::cause(&**self) |
| } |
| } |
| |
| #[stable(feature = "fmt_error", since = "1.11.0")] |
| impl Error for fmt::Error { |
| fn description(&self) -> &str { |
| "an error occurred when formatting an argument" |
| } |
| } |
| |
| #[stable(feature = "try_borrow", since = "1.13.0")] |
| impl Error for cell::BorrowError { |
| fn description(&self) -> &str { |
| "already mutably borrowed" |
| } |
| } |
| |
| #[stable(feature = "try_borrow", since = "1.13.0")] |
| impl Error for cell::BorrowMutError { |
| fn description(&self) -> &str { |
| "already borrowed" |
| } |
| } |
| |
| #[stable(feature = "try_from", since = "1.34.0")] |
| impl Error for char::CharTryFromError { |
| fn description(&self) -> &str { |
| "converted integer out of range for `char`" |
| } |
| } |
| |
| #[stable(feature = "char_from_str", since = "1.20.0")] |
| impl Error for char::ParseCharError { |
| fn description(&self) -> &str { |
| self.__description() |
| } |
| } |
| |
| // copied from any.rs |
| impl dyn Error + 'static { |
| /// Returns `true` if the boxed type is the same as `T` |
| #[stable(feature = "error_downcast", since = "1.3.0")] |
| #[inline] |
| pub fn is<T: Error + 'static>(&self) -> bool { |
| // Get TypeId of the type this function is instantiated with |
| let t = TypeId::of::<T>(); |
| |
| // Get TypeId of the type in the trait object |
| let boxed = self.type_id(); |
| |
| // Compare both TypeIds on equality |
| t == boxed |
| } |
| |
| /// Returns some reference to the boxed value if it is of type `T`, or |
| /// `None` if it isn't. |
| #[stable(feature = "error_downcast", since = "1.3.0")] |
| #[inline] |
| pub fn downcast_ref<T: Error + 'static>(&self) -> Option<&T> { |
| if self.is::<T>() { |
| unsafe { |
| Some(&*(self as *const dyn Error as *const T)) |
| } |
| } else { |
| None |
| } |
| } |
| |
| /// Returns some mutable reference to the boxed value if it is of type `T`, or |
| /// `None` if it isn't. |
| #[stable(feature = "error_downcast", since = "1.3.0")] |
| #[inline] |
| pub fn downcast_mut<T: Error + 'static>(&mut self) -> Option<&mut T> { |
| if self.is::<T>() { |
| unsafe { |
| Some(&mut *(self as *mut dyn Error as *mut T)) |
| } |
| } else { |
| None |
| } |
| } |
| } |
| |
| impl dyn Error + 'static + Send { |
| /// Forwards to the method defined on the type `Any`. |
| #[stable(feature = "error_downcast", since = "1.3.0")] |
| #[inline] |
| pub fn is<T: Error + 'static>(&self) -> bool { |
| <dyn Error + 'static>::is::<T>(self) |
| } |
| |
| /// Forwards to the method defined on the type `Any`. |
| #[stable(feature = "error_downcast", since = "1.3.0")] |
| #[inline] |
| pub fn downcast_ref<T: Error + 'static>(&self) -> Option<&T> { |
| <dyn Error + 'static>::downcast_ref::<T>(self) |
| } |
| |
| /// Forwards to the method defined on the type `Any`. |
| #[stable(feature = "error_downcast", since = "1.3.0")] |
| #[inline] |
| pub fn downcast_mut<T: Error + 'static>(&mut self) -> Option<&mut T> { |
| <dyn Error + 'static>::downcast_mut::<T>(self) |
| } |
| } |
| |
| impl dyn Error + 'static + Send + Sync { |
| /// Forwards to the method defined on the type `Any`. |
| #[stable(feature = "error_downcast", since = "1.3.0")] |
| #[inline] |
| pub fn is<T: Error + 'static>(&self) -> bool { |
| <dyn Error + 'static>::is::<T>(self) |
| } |
| |
| /// Forwards to the method defined on the type `Any`. |
| #[stable(feature = "error_downcast", since = "1.3.0")] |
| #[inline] |
| pub fn downcast_ref<T: Error + 'static>(&self) -> Option<&T> { |
| <dyn Error + 'static>::downcast_ref::<T>(self) |
| } |
| |
| /// Forwards to the method defined on the type `Any`. |
| #[stable(feature = "error_downcast", since = "1.3.0")] |
| #[inline] |
| pub fn downcast_mut<T: Error + 'static>(&mut self) -> Option<&mut T> { |
| <dyn Error + 'static>::downcast_mut::<T>(self) |
| } |
| } |
| |
| impl dyn Error { |
| #[inline] |
| #[stable(feature = "error_downcast", since = "1.3.0")] |
| /// Attempt to downcast the box to a concrete type. |
| pub fn downcast<T: Error + 'static>(self: Box<Self>) -> Result<Box<T>, Box<dyn Error>> { |
| if self.is::<T>() { |
| unsafe { |
| let raw: *mut dyn Error = Box::into_raw(self); |
| Ok(Box::from_raw(raw as *mut T)) |
| } |
| } else { |
| Err(self) |
| } |
| } |
| |
| /// 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()); |
| /// ``` |
| /// |
| /// [`source`]: trait.Error.html#method.source |
| #[unstable(feature = "error_iter", issue = "58520")] |
| #[inline] |
| pub fn iter_chain(&self) -> ErrorIter<'_> { |
| ErrorIter { |
| current: Some(self), |
| } |
| } |
| |
| /// 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()); |
| /// ``` |
| /// |
| /// [`source`]: trait.Error.html#method.source |
| #[inline] |
| #[unstable(feature = "error_iter", issue = "58520")] |
| pub fn iter_sources(&self) -> ErrorIter<'_> { |
| ErrorIter { |
| current: self.source(), |
| } |
| } |
| } |
| |
| /// An iterator over [`Error`] |
| /// |
| /// [`Error`]: trait.Error.html |
| #[unstable(feature = "error_iter", issue = "58520")] |
| #[derive(Copy, Clone, Debug)] |
| pub struct ErrorIter<'a> { |
| current: Option<&'a (dyn Error + 'static)>, |
| } |
| |
| #[unstable(feature = "error_iter", issue = "58520")] |
| impl<'a> Iterator for ErrorIter<'a> { |
| type Item = &'a (dyn Error + 'static); |
| |
| fn next(&mut self) -> Option<Self::Item> { |
| let current = self.current; |
| self.current = self.current.and_then(Error::source); |
| current |
| } |
| } |
| |
| impl dyn Error + Send { |
| #[inline] |
| #[stable(feature = "error_downcast", since = "1.3.0")] |
| /// Attempt to downcast the box to a concrete type. |
| pub fn downcast<T: Error + 'static>(self: Box<Self>) |
| -> Result<Box<T>, Box<dyn Error + Send>> { |
| let err: Box<dyn Error> = self; |
| <dyn Error>::downcast(err).map_err(|s| unsafe { |
| // reapply the Send marker |
| transmute::<Box<dyn Error>, Box<dyn Error + Send>>(s) |
| }) |
| } |
| } |
| |
| impl dyn Error + Send + Sync { |
| #[inline] |
| #[stable(feature = "error_downcast", since = "1.3.0")] |
| /// Attempt to downcast the box to a concrete type. |
| pub fn downcast<T: Error + 'static>(self: Box<Self>) |
| -> Result<Box<T>, Box<Self>> { |
| let err: Box<dyn Error> = self; |
| <dyn Error>::downcast(err).map_err(|s| unsafe { |
| // reapply the Send+Sync marker |
| transmute::<Box<dyn Error>, Box<dyn Error + Send + Sync>>(s) |
| }) |
| } |
| } |
| |
| #[cfg(test)] |
| mod tests { |
| use super::Error; |
| use crate::fmt; |
| |
| #[derive(Debug, PartialEq)] |
| struct A; |
| #[derive(Debug, PartialEq)] |
| struct B; |
| |
| 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 { |
| fn description(&self) -> &str { "A-desc" } |
| } |
| impl Error for B { |
| fn description(&self) -> &str { "A-desc" } |
| } |
| |
| #[test] |
| fn downcasting() { |
| let mut a = A; |
| let a = &mut a as &mut (dyn Error + 'static); |
| assert_eq!(a.downcast_ref::<A>(), Some(&A)); |
| assert_eq!(a.downcast_ref::<B>(), None); |
| assert_eq!(a.downcast_mut::<A>(), Some(&mut A)); |
| assert_eq!(a.downcast_mut::<B>(), None); |
| |
| let a: Box<dyn Error> = Box::new(A); |
| match a.downcast::<B>() { |
| Ok(..) => panic!("expected error"), |
| Err(e) => assert_eq!(*e.downcast::<A>().unwrap(), A), |
| } |
| } |
| } |
