/// }
/// ```
#[stable(feature = "rust1", since = "1.0.0")]
- fn cause(&self) -> Option<&dyn Error> { None }
+ #[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 = "rust1", since = "1.30.0")]
+ fn source(&self) -> Option<&(dyn Error + 'static)> { None }
/// Get the `TypeId` of `self`
#[doc(hidden)]