882 lines
26 KiB
Rust
882 lines
26 KiB
Rust
//! Traits for working with Errors.
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#![stable(feature = "rust1", since = "1.0.0")]
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// A note about crates and the facade:
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//
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// Originally, the `Error` trait was defined in libcore, and the impls
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// were scattered about. However, coherence objected to this
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// arrangement, because to create the blanket impls for `Box` required
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// knowing that `&str: !Error`, and we have no means to deal with that
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// sort of conflict just now. Therefore, for the time being, we have
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// moved the `Error` trait into libstd. As we evolve a sol'n to the
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// coherence challenge (e.g., specialization, neg impls, etc) we can
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// reconsider what crate these items belong in.
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use core::array;
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use crate::alloc::{AllocErr, LayoutErr, CannotReallocInPlace};
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use crate::any::TypeId;
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use crate::backtrace::Backtrace;
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use crate::borrow::Cow;
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use crate::cell;
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use crate::char;
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use crate::fmt::{self, Debug, Display};
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use crate::mem::transmute;
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use crate::num;
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use crate::str;
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use crate::string;
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/// `Error` is a trait representing the basic expectations for error values,
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/// i.e., values of type `E` in [`Result<T, E>`]. Errors must describe
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/// themselves through the [`Display`] and [`Debug`] traits, and may provide
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/// cause chain information:
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///
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/// The [`source`] method is generally used when errors cross "abstraction
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/// boundaries". If one module must report an error that is caused by an error
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/// from a lower-level module, it can allow access to that error via the
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/// [`source`] method. This makes it possible for the high-level module to
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/// provide its own errors while also revealing some of the implementation for
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/// debugging via [`source`] chains.
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///
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/// [`Result<T, E>`]: ../result/enum.Result.html
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/// [`Display`]: ../fmt/trait.Display.html
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/// [`Debug`]: ../fmt/trait.Debug.html
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/// [`source`]: trait.Error.html#method.source
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#[stable(feature = "rust1", since = "1.0.0")]
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pub trait Error: Debug + Display {
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/// **This method is soft-deprecated.**
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///
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/// Although using it won’t cause compilation warning,
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/// new code should use [`Display`] instead
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/// and new `impl`s can omit it.
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///
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/// To obtain error description as a string, use `to_string()`.
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///
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/// [`Display`]: ../fmt/trait.Display.html
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///
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/// # Examples
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///
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/// ```
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/// match "xc".parse::<u32>() {
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/// Err(e) => {
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/// // Print `e` itself, not `e.description()`.
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/// println!("Error: {}", e);
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/// }
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/// _ => println!("No error"),
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/// }
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/// ```
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#[stable(feature = "rust1", since = "1.0.0")]
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fn description(&self) -> &str {
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"description() is deprecated; use Display"
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}
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/// The lower-level cause of this error, if any.
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///
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/// # Examples
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///
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/// ```
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/// use std::error::Error;
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/// use std::fmt;
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///
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/// #[derive(Debug)]
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/// struct SuperError {
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/// side: SuperErrorSideKick,
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/// }
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///
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/// impl fmt::Display for SuperError {
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/// fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
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/// write!(f, "SuperError is here!")
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/// }
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/// }
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///
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/// impl Error for SuperError {
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/// fn description(&self) -> &str {
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/// "I'm the superhero of errors"
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/// }
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///
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/// fn cause(&self) -> Option<&dyn Error> {
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/// Some(&self.side)
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/// }
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/// }
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///
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/// #[derive(Debug)]
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/// struct SuperErrorSideKick;
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///
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/// impl fmt::Display for SuperErrorSideKick {
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/// fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
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/// write!(f, "SuperErrorSideKick is here!")
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/// }
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/// }
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///
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/// impl Error for SuperErrorSideKick {
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/// fn description(&self) -> &str {
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/// "I'm SuperError side kick"
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/// }
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/// }
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///
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/// fn get_super_error() -> Result<(), SuperError> {
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/// Err(SuperError { side: SuperErrorSideKick })
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/// }
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///
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/// fn main() {
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/// match get_super_error() {
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/// Err(e) => {
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/// println!("Error: {}", e.description());
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/// println!("Caused by: {}", e.cause().unwrap());
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/// }
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/// _ => println!("No error"),
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/// }
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/// }
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/// ```
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#[stable(feature = "rust1", since = "1.0.0")]
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#[rustc_deprecated(since = "1.33.0", reason = "replaced by Error::source, which can support \
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downcasting")]
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fn cause(&self) -> Option<&dyn Error> {
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self.source()
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}
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/// The lower-level source of this error, if any.
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///
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/// # Examples
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///
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/// ```
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/// use std::error::Error;
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/// use std::fmt;
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///
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/// #[derive(Debug)]
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/// struct SuperError {
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/// side: SuperErrorSideKick,
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/// }
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///
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/// impl fmt::Display for SuperError {
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/// fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
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/// write!(f, "SuperError is here!")
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/// }
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/// }
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///
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/// impl Error for SuperError {
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/// fn description(&self) -> &str {
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/// "I'm the superhero of errors"
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/// }
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///
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/// fn source(&self) -> Option<&(dyn Error + 'static)> {
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/// Some(&self.side)
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/// }
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/// }
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///
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/// #[derive(Debug)]
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/// struct SuperErrorSideKick;
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///
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/// impl fmt::Display for SuperErrorSideKick {
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/// fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
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/// write!(f, "SuperErrorSideKick is here!")
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/// }
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/// }
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///
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/// impl Error for SuperErrorSideKick {
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/// fn description(&self) -> &str {
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/// "I'm SuperError side kick"
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/// }
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/// }
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///
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/// fn get_super_error() -> Result<(), SuperError> {
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/// Err(SuperError { side: SuperErrorSideKick })
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/// }
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///
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/// fn main() {
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/// match get_super_error() {
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/// Err(e) => {
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/// println!("Error: {}", e.description());
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/// println!("Caused by: {}", e.source().unwrap());
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/// }
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/// _ => println!("No error"),
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/// }
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/// }
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/// ```
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#[stable(feature = "error_source", since = "1.30.0")]
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fn source(&self) -> Option<&(dyn Error + 'static)> { None }
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/// Gets the `TypeId` of `self`.
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#[doc(hidden)]
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#[unstable(feature = "error_type_id",
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reason = "this is memory-unsafe to override in user code",
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issue = "60784")]
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fn type_id(&self, _: private::Internal) -> TypeId where Self: 'static {
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TypeId::of::<Self>()
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}
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/// Returns a stack backtrace, if available, of where this error occurred.
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///
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/// This function allows inspecting the location, in code, of where an error
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/// happened. The returned `Backtrace` contains information about the stack
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/// trace of the OS thread of execution of where the error originated from.
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///
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/// Note that not all errors contain a `Backtrace`. Also note that a
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/// `Backtrace` may actually be empty. For more information consult the
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/// `Backtrace` type itself.
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#[unstable(feature = "backtrace", issue = "53487")]
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fn backtrace(&self) -> Option<&Backtrace> {
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None
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}
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}
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mod private {
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// This is a hack to prevent `type_id` from being overridden by `Error`
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// implementations, since that can enable unsound downcasting.
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#[unstable(feature = "error_type_id", issue = "60784")]
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#[derive(Debug)]
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pub struct Internal;
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}
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#[stable(feature = "rust1", since = "1.0.0")]
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impl<'a, E: Error + 'a> From<E> for Box<dyn Error + 'a> {
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/// Converts a type of [`Error`] into a box of dyn [`Error`].
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///
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/// [`Error`]: ../error/trait.Error.html
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///
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/// # Examples
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///
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/// ```
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/// use std::error::Error;
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/// use std::fmt;
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/// use std::mem;
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///
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/// #[derive(Debug)]
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/// struct AnError;
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///
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/// impl fmt::Display for AnError {
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/// fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
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/// write!(f , "An error")
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/// }
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/// }
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///
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/// impl Error for AnError {
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/// fn description(&self) -> &str {
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/// "Description of an error"
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/// }
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/// }
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///
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/// let an_error = AnError;
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/// assert!(0 == mem::size_of_val(&an_error));
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/// let a_boxed_error = Box::<dyn Error>::from(an_error);
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/// assert!(mem::size_of::<Box<dyn Error>>() == mem::size_of_val(&a_boxed_error))
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/// ```
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fn from(err: E) -> Box<dyn Error + 'a> {
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Box::new(err)
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}
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}
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#[stable(feature = "rust1", since = "1.0.0")]
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impl<'a, E: Error + Send + Sync + 'a> From<E> for Box<dyn Error + Send + Sync + 'a> {
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/// Converts a type of [`Error`] + [`Send`] + [`Sync`] into a box of
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/// dyn [`Error`] + [`Send`] + [`Sync`].
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///
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/// [`Error`]: ../error/trait.Error.html
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///
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/// # Examples
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///
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/// ```
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/// use std::error::Error;
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/// use std::fmt;
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/// use std::mem;
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///
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/// #[derive(Debug)]
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/// struct AnError;
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///
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/// impl fmt::Display for AnError {
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/// fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
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/// write!(f , "An error")
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/// }
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/// }
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///
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/// impl Error for AnError {
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/// fn description(&self) -> &str {
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/// "Description of an error"
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/// }
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/// }
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///
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/// unsafe impl Send for AnError {}
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///
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/// unsafe impl Sync for AnError {}
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///
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/// let an_error = AnError;
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/// assert!(0 == mem::size_of_val(&an_error));
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/// let a_boxed_error = Box::<dyn Error + Send + Sync>::from(an_error);
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/// assert!(
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/// mem::size_of::<Box<dyn Error + Send + Sync>>() == mem::size_of_val(&a_boxed_error))
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/// ```
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fn from(err: E) -> Box<dyn Error + Send + Sync + 'a> {
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Box::new(err)
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}
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}
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#[stable(feature = "rust1", since = "1.0.0")]
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impl From<String> for Box<dyn Error + Send + Sync> {
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/// Converts a [`String`] into a box of dyn [`Error`] + [`Send`] + [`Sync`].
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///
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/// [`Error`]: ../error/trait.Error.html
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///
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/// # Examples
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///
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/// ```
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/// use std::error::Error;
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/// use std::mem;
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///
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/// let a_string_error = "a string error".to_string();
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/// let a_boxed_error = Box::<dyn Error + Send + Sync>::from(a_string_error);
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/// assert!(
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/// mem::size_of::<Box<dyn Error + Send + Sync>>() == mem::size_of_val(&a_boxed_error))
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/// ```
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fn from(err: String) -> Box<dyn Error + Send + Sync> {
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struct StringError(String);
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impl Error for StringError {
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fn description(&self) -> &str { &self.0 }
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}
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impl Display for StringError {
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fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
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Display::fmt(&self.0, f)
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}
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}
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// Purposefully skip printing "StringError(..)"
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impl Debug for StringError {
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fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
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Debug::fmt(&self.0, f)
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}
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}
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Box::new(StringError(err))
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}
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}
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#[stable(feature = "string_box_error", since = "1.6.0")]
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impl From<String> for Box<dyn Error> {
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/// Converts a [`String`] into a box of dyn [`Error`].
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///
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/// [`Error`]: ../error/trait.Error.html
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///
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/// # Examples
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///
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/// ```
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/// use std::error::Error;
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/// use std::mem;
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///
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/// let a_string_error = "a string error".to_string();
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/// let a_boxed_error = Box::<dyn Error>::from(a_string_error);
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/// assert!(mem::size_of::<Box<dyn Error>>() == mem::size_of_val(&a_boxed_error))
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/// ```
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fn from(str_err: String) -> Box<dyn Error> {
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let err1: Box<dyn Error + Send + Sync> = From::from(str_err);
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let err2: Box<dyn Error> = err1;
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err2
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}
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}
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#[stable(feature = "rust1", since = "1.0.0")]
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impl<'a> From<&str> for Box<dyn Error + Send + Sync + 'a> {
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/// Converts a [`str`] into a box of dyn [`Error`] + [`Send`] + [`Sync`].
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///
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/// [`Error`]: ../error/trait.Error.html
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///
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/// # Examples
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///
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/// ```
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/// use std::error::Error;
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/// use std::mem;
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///
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/// let a_str_error = "a str error";
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/// let a_boxed_error = Box::<dyn Error + Send + Sync>::from(a_str_error);
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/// assert!(
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/// mem::size_of::<Box<dyn Error + Send + Sync>>() == mem::size_of_val(&a_boxed_error))
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/// ```
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fn from(err: &str) -> Box<dyn Error + Send + Sync + 'a> {
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From::from(String::from(err))
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}
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}
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#[stable(feature = "string_box_error", since = "1.6.0")]
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impl From<&str> for Box<dyn Error> {
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/// Converts a [`str`] into a box of dyn [`Error`].
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///
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/// [`Error`]: ../error/trait.Error.html
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///
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/// # Examples
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///
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/// ```
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/// use std::error::Error;
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/// use std::mem;
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///
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/// let a_str_error = "a str error";
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/// let a_boxed_error = Box::<dyn Error>::from(a_str_error);
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/// assert!(mem::size_of::<Box<dyn Error>>() == mem::size_of_val(&a_boxed_error))
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/// ```
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fn from(err: &str) -> Box<dyn Error> {
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From::from(String::from(err))
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}
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}
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#[stable(feature = "cow_box_error", since = "1.22.0")]
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impl<'a, 'b> From<Cow<'b, str>> for Box<dyn Error + Send + Sync + 'a> {
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/// Converts a [`Cow`] into a box of dyn [`Error`] + [`Send`] + [`Sync`].
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///
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/// [`Cow`]: ../borrow/enum.Cow.html
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/// [`Error`]: ../error/trait.Error.html
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///
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/// # Examples
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///
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/// ```
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/// use std::error::Error;
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/// use std::mem;
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/// use std::borrow::Cow;
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///
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/// let a_cow_str_error = Cow::from("a str error");
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/// let a_boxed_error = Box::<dyn Error + Send + Sync>::from(a_cow_str_error);
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/// assert!(
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/// mem::size_of::<Box<dyn Error + Send + Sync>>() == mem::size_of_val(&a_boxed_error))
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/// ```
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fn from(err: Cow<'b, str>) -> Box<dyn Error + Send + Sync + 'a> {
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From::from(String::from(err))
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}
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}
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#[stable(feature = "cow_box_error", since = "1.22.0")]
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impl<'a> From<Cow<'a, str>> for Box<dyn Error> {
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/// Converts a [`Cow`] into a box of dyn [`Error`].
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///
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/// [`Cow`]: ../borrow/enum.Cow.html
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/// [`Error`]: ../error/trait.Error.html
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///
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/// # Examples
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///
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/// ```
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/// use std::error::Error;
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/// use std::mem;
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/// use std::borrow::Cow;
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///
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/// let a_cow_str_error = Cow::from("a str error");
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/// let a_boxed_error = Box::<dyn Error>::from(a_cow_str_error);
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/// assert!(mem::size_of::<Box<dyn Error>>() == mem::size_of_val(&a_boxed_error))
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/// ```
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fn from(err: Cow<'a, str>) -> Box<dyn Error> {
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From::from(String::from(err))
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}
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}
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#[unstable(feature = "never_type", issue = "35121")]
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impl Error for ! {
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fn description(&self) -> &str { *self }
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}
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#[unstable(feature = "allocator_api",
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reason = "the precise API and guarantees it provides may be tweaked.",
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issue = "32838")]
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impl Error for AllocErr {
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fn description(&self) -> &str {
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"memory allocation failed"
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}
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}
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#[unstable(feature = "allocator_api",
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reason = "the precise API and guarantees it provides may be tweaked.",
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issue = "32838")]
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impl Error for LayoutErr {
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fn description(&self) -> &str {
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"invalid parameters to Layout::from_size_align"
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}
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}
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#[unstable(feature = "allocator_api",
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reason = "the precise API and guarantees it provides may be tweaked.",
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issue = "32838")]
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impl Error for CannotReallocInPlace {
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fn description(&self) -> &str {
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CannotReallocInPlace::description(self)
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}
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}
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#[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)
|
||
}
|
||
|
||
fn source(&self) -> Option<&(dyn Error + 'static)> {
|
||
Error::source(&**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(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 {
|
||
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),
|
||
}
|
||
}
|
||
}
|