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Diffstat (limited to 'src/libstd/error.rs')
| -rw-r--r-- | src/libstd/error.rs | 802 |
1 files changed, 0 insertions, 802 deletions
diff --git a/src/libstd/error.rs b/src/libstd/error.rs deleted file mode 100644 index 3b4cb859dd4..00000000000 --- a/src/libstd/error.rs +++ /dev/null @@ -1,802 +0,0 @@ -//! 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 core::convert::Infallible; - -use crate::alloc::{AllocErr, LayoutErr}; -use crate::any::TypeId; -use crate::backtrace::Backtrace; -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 { - /// 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 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 get_super_error() -> Result<(), SuperError> { - /// Err(SuperError { side: SuperErrorSideKick }) - /// } - /// - /// fn main() { - /// match get_super_error() { - /// Err(e) => { - /// println!("Error: {}", e); - /// 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, _: private::Internal) -> TypeId - where - Self: 'static, - { - TypeId::of::<Self>() - } - - /// Returns a stack backtrace, if available, of where this error occurred. - /// - /// This function allows inspecting the location, in code, of where an error - /// happened. The returned `Backtrace` contains information about the stack - /// trace of the OS thread of execution of where the error originated from. - /// - /// Note that not all errors contain a `Backtrace`. Also note that a - /// `Backtrace` may actually be empty. For more information consult the - /// `Backtrace` type itself. - #[unstable(feature = "backtrace", issue = "53487")] - fn backtrace(&self) -> Option<&Backtrace> { - None - } - - /// ``` - /// if let Err(e) = "xc".parse::<u32>() { - /// // Print `e` itself, no need for description(). - /// eprintln!("Error: {}", e); - /// } - /// ``` - #[stable(feature = "rust1", since = "1.0.0")] - #[rustc_deprecated(since = "1.42.0", reason = "use the Display impl or to_string()")] - fn description(&self) -> &str { - "description() is deprecated; use Display" - } - - #[stable(feature = "rust1", since = "1.0.0")] - #[rustc_deprecated( - since = "1.33.0", - reason = "replaced by Error::source, which can support downcasting" - )] - #[allow(missing_docs)] - fn cause(&self) -> Option<&dyn Error> { - self.source() - } -} - -mod private { - // This is a hack to prevent `type_id` from being overridden by `Error` - // implementations, since that can enable unsound downcasting. - #[unstable(feature = "error_type_id", issue = "60784")] - #[derive(Debug)] - pub struct Internal; -} - -#[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`]. - /// - /// [`Error`]: ../error/trait.Error.html - /// - /// # 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 {} - /// - /// let an_error = AnError; - /// assert!(0 == mem::size_of_val(&an_error)); - /// let a_boxed_error = Box::<dyn 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`]. - /// - /// [`Error`]: ../error/trait.Error.html - /// - /// # 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 {} - /// - /// 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::<dyn 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`]. - /// - /// [`Error`]: ../error/trait.Error.html - /// - /// # Examples - /// - /// ``` - /// use std::error::Error; - /// use std::mem; - /// - /// let a_string_error = "a string error".to_string(); - /// let a_boxed_error = Box::<dyn Error + Send + Sync>::from(a_string_error); - /// assert!( - /// mem::size_of::<Box<dyn Error + Send + Sync>>() == mem::size_of_val(&a_boxed_error)) - /// ``` - #[inline] - fn from(err: String) -> Box<dyn Error + Send + Sync> { - struct StringError(String); - - impl Error for StringError { - #[allow(deprecated)] - fn description(&self) -> &str { - &self.0 - } - } - - impl Display for StringError { - fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result { - Display::fmt(&self.0, f) - } - } - - // Purposefully skip printing "StringError(..)" - impl Debug for StringError { - fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result { - Debug::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`]. - /// - /// [`Error`]: ../error/trait.Error.html - /// - /// # Examples - /// - /// ``` - /// use std::error::Error; - /// use std::mem; - /// - /// let a_string_error = "a string error".to_string(); - /// let a_boxed_error = Box::<dyn 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`]. - /// - /// [`Error`]: ../error/trait.Error.html - /// - /// # Examples - /// - /// ``` - /// use std::error::Error; - /// use std::mem; - /// - /// let a_str_error = "a str error"; - /// let a_boxed_error = Box::<dyn Error + Send + Sync>::from(a_str_error); - /// assert!( - /// mem::size_of::<Box<dyn Error + Send + Sync>>() == mem::size_of_val(&a_boxed_error)) - /// ``` - #[inline] - 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`]. - /// - /// [`Error`]: ../error/trait.Error.html - /// - /// # Examples - /// - /// ``` - /// use std::error::Error; - /// use std::mem; - /// - /// let a_str_error = "a str error"; - /// let a_boxed_error = Box::<dyn 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`]. - /// - /// [`Cow`]: ../borrow/enum.Cow.html - /// [`Error`]: ../error/trait.Error.html - /// - /// # 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::<dyn 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`]. - /// - /// [`Cow`]: ../borrow/enum.Cow.html - /// [`Error`]: ../error/trait.Error.html - /// - /// # 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::<dyn 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 ! {} - -#[unstable( - feature = "allocator_api", - reason = "the precise API and guarantees it provides may be tweaked.", - issue = "32838" -)] -impl Error for AllocErr {} - -#[unstable( - feature = "allocator_api", - reason = "the precise API and guarantees it provides may be tweaked.", - issue = "32838" -)] -impl Error for LayoutErr {} - -#[stable(feature = "rust1", since = "1.0.0")] -impl Error for str::ParseBoolError { - #[allow(deprecated)] - fn description(&self) -> &str { - "failed to parse bool" - } -} - -#[stable(feature = "rust1", since = "1.0.0")] -impl Error for str::Utf8Error { - #[allow(deprecated)] - fn description(&self) -> &str { - "invalid utf-8: corrupt contents" - } -} - -#[stable(feature = "rust1", since = "1.0.0")] -impl Error for num::ParseIntError { - #[allow(deprecated)] - fn description(&self) -> &str { - self.__description() - } -} - -#[stable(feature = "try_from", since = "1.34.0")] -impl Error for num::TryFromIntError { - #[allow(deprecated)] - fn description(&self) -> &str { - self.__description() - } -} - -#[stable(feature = "try_from", since = "1.34.0")] -impl Error for array::TryFromSliceError { - #[allow(deprecated)] - fn description(&self) -> &str { - self.__description() - } -} - -#[stable(feature = "rust1", since = "1.0.0")] -impl Error for num::ParseFloatError { - #[allow(deprecated)] - fn description(&self) -> &str { - self.__description() - } -} - -#[stable(feature = "rust1", since = "1.0.0")] -impl Error for string::FromUtf8Error { - #[allow(deprecated)] - fn description(&self) -> &str { - "invalid utf-8" - } -} - -#[stable(feature = "rust1", since = "1.0.0")] -impl Error for string::FromUtf16Error { - #[allow(deprecated)] - fn description(&self) -> &str { - "invalid utf-16" - } -} - -#[stable(feature = "str_parse_error2", since = "1.8.0")] -impl Error for Infallible { - fn description(&self) -> &str { - match *self {} - } -} - -#[stable(feature = "decode_utf16", since = "1.9.0")] -impl Error for char::DecodeUtf16Error { - #[allow(deprecated)] - fn description(&self) -> &str { - "unpaired surrogate found" - } -} - -#[stable(feature = "box_error", since = "1.8.0")] -impl<T: Error> Error for Box<T> { - #[allow(deprecated, deprecated_in_future)] - fn description(&self) -> &str { - Error::description(&**self) - } - - #[allow(deprecated)] - fn cause(&self) -> Option<&dyn Error> { - Error::cause(&**self) - } - - fn source(&self) -> Option<&(dyn Error + 'static)> { - Error::source(&**self) - } -} - -#[stable(feature = "fmt_error", since = "1.11.0")] -impl Error for fmt::Error { - #[allow(deprecated)] - fn description(&self) -> &str { - "an error occurred when formatting an argument" - } -} - -#[stable(feature = "try_borrow", since = "1.13.0")] -impl Error for cell::BorrowError { - #[allow(deprecated)] - fn description(&self) -> &str { - "already mutably borrowed" - } -} - -#[stable(feature = "try_borrow", since = "1.13.0")] -impl Error for cell::BorrowMutError { - #[allow(deprecated)] - fn description(&self) -> &str { - "already borrowed" - } -} - -#[stable(feature = "try_from", since = "1.34.0")] -impl Error for char::CharTryFromError { - #[allow(deprecated)] - 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 { - #[allow(deprecated)] - fn description(&self) -> &str { - self.__description() - } -} - -#[unstable(feature = "try_reserve", reason = "new API", issue = "48043")] -impl Error for alloc::collections::TryReserveError {} - -// 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(private::Internal); - - // Compare both `TypeId`s 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 `dyn Error`. - #[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 `dyn Error`. - #[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 `dyn Error`. - #[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 `dyn Error`. - #[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 `dyn Error`. - #[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 `dyn Error`. - #[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")] - /// Attempts 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`]. - /// - /// If you want to omit the current error and only use its sources, - /// use `skip(1)`. - /// - /// # 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.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 chain(&self) -> Chain<'_> { - Chain { current: Some(self) } - } -} - -/// An iterator over an [`Error`] and its sources. -/// -/// If you want to omit the initial error and only process -/// its sources, use `skip(1)`. -/// -/// [`Error`]: trait.Error.html -#[unstable(feature = "error_iter", issue = "58520")] -#[derive(Clone, Debug)] -pub struct Chain<'a> { - current: Option<&'a (dyn Error + 'static)>, -} - -#[unstable(feature = "error_iter", issue = "58520")] -impl<'a> Iterator for Chain<'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")] - /// Attempts 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")] - /// Attempts 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 {} - impl Error for B {} - - #[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), - } - } -} |