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< title > The root cause of all Errors - chainerror< / title >
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< h1 id = "the-root-cause-of-all-errors" > < a class = "header" href = "#the-root-cause-of-all-errors" > The root cause of all Errors< / a > < / h1 >
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< p > < code > chainerror< / code > also has some helper methods:< / p >
< pre > < code class = "language-rust ignore" > fn is_chain< T: 'static + Display + Debug> (& self) -> bool
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fn downcast_chain_ref< T: 'static + Display + Debug> (& self) -> Option< & chainerror::Error< T> >
fn downcast_chain_mut< T: 'static + Display + Debug> (& mut self) -> Option< & mut chainerror::Error< T> >
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fn root_cause(& self) -> Option< & (dyn Error + 'static)>
fn find_cause< U: Error + 'static> (& self) -> Option< & U>
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fn find_chain_cause< U: Error + 'static> (& self) -> Option< & chainerror::Error< U> >
fn kind< 'a> (& 'a self) -> & 'a T< / code > < / pre >
< p > Using < code > downcast_chain_ref::< String> ()< / code > gives a < code > chainerror::Error< String> < / code > , which can be used
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to call < code > .find_cause::< io::Error> ()< / code > . < / p >
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< pre > < code class = "language-rust ignore" > if let Some(s) = e.downcast_chain_ref::< String> () {
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if let Some(ioerror) = s.find_cause::< io::Error> () {< / code > < / pre >
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< p > or to use < code > .root_cause()< / code > , which of course can be of any type implementing < code > std::error::Error< / code > .< / p >
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< pre > < code class = "language-rust ignore" > if let Some(e) = s.root_cause() {< / code > < / pre >
< pre > < pre class = "playground" > < code class = "language-rust" > #![allow(clippy::single_match)]
#![allow(clippy::redundant_pattern_matching)]
use chainerror::{Context as _, ErrorDown as _};
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use std::error::Error;
use std::io;
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fn do_some_io() -> Result< (), Box< dyn Error + Send + Sync> > {
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Err(io::Error::from(io::ErrorKind::NotFound))?;
Ok(())
}
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fn func2() -> Result< (), Box< dyn Error + Send + Sync> > {
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let filename = " foo.txt" ;
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do_some_io().context(format!(" Error reading '{}'" , filename))?;
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Ok(())
}
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fn func1() -> Result< (), Box< dyn Error + Send + Sync> > {
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func2().context(" func1 error" )?;
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Ok(())
}
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fn main() -> Result< (), Box< dyn Error + Send + Sync> > {
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if let Err(e) = func1() {
eprintln!(" Error: {}" , e);
if let Some(s) = e.downcast_chain_ref::< String> () {
if let Some(ioerror) = s.find_cause::< io::Error> () {
eprintln!(" caused by: std::io::Error: {}" , ioerror);
match ioerror.kind() {
io::ErrorKind::NotFound => eprintln!(" of kind: std::io::ErrorKind::NotFound" ),
_ => {}
}
}
if let Some(e) = s.root_cause() {
let ioerror = e.downcast_ref::< io::Error> ().unwrap();
eprintln!(" The root cause was: std::io::Error: {:#?}" , ioerror);
}
}
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std::process::exit(1);
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}
Ok(())
}
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< span class = "boring" > #[allow(dead_code)]
< / span > < span class = "boring" > mod chainerror {
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< / span > < span class = "boring" > #![doc = include_str!(" ../README.md" )]
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< / span > < span class = "boring" > #![deny(clippy::all)]
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< / span > < span class = "boring" > #![allow(clippy::needless_doctest_main)]
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< / span > < span class = "boring" > #![deny(missing_docs)]
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< / span > < span class = "boring" >
< / span > < span class = "boring" > use std::any::TypeId;
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< / span > < span class = "boring" > use std::error::Error as StdError;
< / span > < span class = "boring" > use std::fmt::{Debug, Display, Formatter};
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< / span > < span class = "boring" > use std::panic::Location;
< / span > < span class = "boring" >
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< / span > < span class = "boring" > /// chains an inner error kind `T` with a causing error
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< / span > < span class = "boring" > pub struct Error< T> {
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< / span > < span class = "boring" > occurrence: Option< String> ,
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< / span > < span class = "boring" > kind: T,
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< / span > < span class = "boring" > error_cause: Option< Box< dyn StdError + 'static + Send + Sync> > ,
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< / span > < span class = "boring" > }
< / span > < span class = "boring" >
< / span > < span class = "boring" > /// convenience type alias
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< / span > < span class = "boring" > pub type Result< O, E> = std::result::Result< O, Error< E> > ;
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< / span > < span class = "boring" >
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< / span > < span class = "boring" > impl< T: 'static + Display + Debug> Error< T> {
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< / span > < span class = "boring" > /// Use the `context()` or `map_context()` Result methods instead of calling this directly
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< / span > < span class = "boring" > #[inline]
< / span > < span class = "boring" > pub fn new(
< / span > < span class = "boring" > kind: T,
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< / span > < span class = "boring" > error_cause: Option< Box< dyn StdError + 'static + Send + Sync> > ,
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< / span > < span class = "boring" > occurrence: Option< String> ,
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< / span > < span class = "boring" > ) -> Self {
< / span > < span class = "boring" > Self {
< / span > < span class = "boring" > occurrence,
< / span > < span class = "boring" > kind,
< / span > < span class = "boring" > error_cause,
< / span > < span class = "boring" > }
< / span > < span class = "boring" > }
< / span > < span class = "boring" >
< / span > < span class = "boring" > /// return the root cause of the error chain, if any exists
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< / span > < span class = "boring" > pub fn root_cause(& self) -> Option< & (dyn StdError + 'static)> {
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< / span > < span class = "boring" > self.iter().last()
< / span > < span class = "boring" > }
< / span > < span class = "boring" >
< / span > < span class = "boring" > /// Find the first error cause of type U, if any exists
< / span > < span class = "boring" > ///
< / span > < span class = "boring" > /// # Examples
< / span > < span class = "boring" > ///
< / span > < span class = "boring" > /// ```rust
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< / span > < span class = "boring" > /// use chainerror::Context as _;
< / span > < span class = "boring" > /// use chainerror::ErrorDown as _;
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< / span > < span class = "boring" > /// use std::error::Error;
< / span > < span class = "boring" > /// use std::io;
< / span > < span class = "boring" > ///
< / span > < span class = "boring" > /// fn do_some_io() -> Result< (), Box< dyn Error + Send + Sync> > {
< / span > < span class = "boring" > /// Err(io::Error::from(io::ErrorKind::NotFound))?;
< / span > < span class = "boring" > /// Ok(())
< / span > < span class = "boring" > /// }
< / span > < span class = "boring" > ///
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< / span > < span class = "boring" > /// chainerror::str_context!(Func2Error);
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< / span > < span class = "boring" > ///
< / span > < span class = "boring" > /// fn func2() -> Result< (), Box< dyn Error + Send + Sync> > {
< / span > < span class = "boring" > /// let filename = " foo.txt" ;
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< / span > < span class = "boring" > /// do_some_io().context(Func2Error(format!(" Error reading '{}'" , filename)))?;
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< / span > < span class = "boring" > /// Ok(())
< / span > < span class = "boring" > /// }
< / span > < span class = "boring" > ///
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< / span > < span class = "boring" > /// chainerror::str_context!(Func1Error);
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< / span > < span class = "boring" > ///
< / span > < span class = "boring" > /// fn func1() -> Result< (), Box< dyn Error + Send + Sync> > {
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< / span > < span class = "boring" > /// func2().context(Func1Error::new(" func1 error" ))?;
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< / span > < span class = "boring" > /// Ok(())
< / span > < span class = "boring" > /// }
< / span > < span class = "boring" > ///
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< / span > < span class = "boring" > /// if let Err(e) = func1() {
< / span > < span class = "boring" > /// if let Some(f1err) = e.downcast_chain_ref::< Func1Error> () {
< / span > < span class = "boring" > /// assert!(f1err.find_cause::< io::Error> ().is_some());
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< / span > < span class = "boring" > ///
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< / span > < span class = "boring" > /// assert!(f1err.find_chain_cause::< Func2Error> ().is_some());
< / span > < span class = "boring" > /// }
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< / span > < span class = "boring" > /// # else {
< / span > < span class = "boring" > /// # panic!();
< / span > < span class = "boring" > /// # }
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< / span > < span class = "boring" > /// }
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< / span > < span class = "boring" > /// # else {
< / span > < span class = "boring" > /// # unreachable!();
< / span > < span class = "boring" > /// # }
< / span > < span class = "boring" > /// ```
< / span > < span class = "boring" > #[inline]
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< / span > < span class = "boring" > pub fn find_cause< U: StdError + 'static> (& self) -> Option< & U> {
< / span > < span class = "boring" > self.iter()
< / span > < span class = "boring" > .filter_map(< dyn StdError> ::downcast_ref::< U> )
< / span > < span class = "boring" > .next()
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< / span > < span class = "boring" > }
< / span > < span class = "boring" >
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< / span > < span class = "boring" > /// Find the first error cause of type [`Error< U> `](Error), if any exists
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< / span > < span class = "boring" > ///
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< / span > < span class = "boring" > /// Same as `find_cause`, but hides the [`Error< U> `](Error) implementation internals
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< / span > < span class = "boring" > ///
< / span > < span class = "boring" > /// # Examples
< / span > < span class = "boring" > ///
< / span > < span class = "boring" > /// ```rust
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< / span > < span class = "boring" > /// # chainerror::str_context!(FooError);
< / span > < span class = "boring" > /// # let err = chainerror::Error::new(String::new(), None, None);
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< / span > < span class = "boring" > /// // Instead of writing
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< / span > < span class = "boring" > /// err.find_cause::< chainerror::Error< FooError> > ();
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< / span > < span class = "boring" > ///
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< / span > < span class = "boring" > /// // leave out the chainerror::Error< FooError> implementation detail
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< / span > < span class = "boring" > /// err.find_chain_cause::< FooError> ();
< / span > < span class = "boring" > /// ```
< / span > < span class = "boring" > #[inline]
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< / span > < span class = "boring" > pub fn find_chain_cause< U: StdError + 'static> (& self) -> Option< & Error< U> > {
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< / span > < span class = "boring" > self.iter()
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< / span > < span class = "boring" > .filter_map(< dyn StdError> ::downcast_ref::< Error< U> > )
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< / span > < span class = "boring" > .next()
< / span > < span class = "boring" > }
< / span > < span class = "boring" >
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< / span > < span class = "boring" > /// Find the first error cause of type [`Error< U> `](Error) or `U`, if any exists and return `U`
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< / span > < span class = "boring" > ///
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< / span > < span class = "boring" > /// Same as `find_cause` and `find_chain_cause`, but hides the [`Error< U> `](Error) implementation internals
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< / span > < span class = "boring" > ///
< / span > < span class = "boring" > /// # Examples
< / span > < span class = "boring" > ///
< / span > < span class = "boring" > /// ```rust
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< / span > < span class = "boring" > /// # chainerror::str_context!(FooErrorKind);
< / span > < span class = "boring" > /// # let err = chainerror::Error::new(String::new(), None, None);
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< / span > < span class = "boring" > /// // Instead of writing
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< / span > < span class = "boring" > /// err.find_cause::< chainerror::Error< FooErrorKind> > ();
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< / span > < span class = "boring" > /// // and/or
< / span > < span class = "boring" > /// err.find_chain_cause::< FooErrorKind> ();
< / span > < span class = "boring" > /// // and/or
< / span > < span class = "boring" > /// err.find_cause::< FooErrorKind> ();
< / span > < span class = "boring" > ///
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< / span > < span class = "boring" > /// // leave out the chainerror::Error< FooErrorKind> implementation detail
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< / span > < span class = "boring" > /// err.find_kind_or_cause::< FooErrorKind> ();
< / span > < span class = "boring" > /// ```
< / span > < span class = "boring" > #[inline]
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< / span > < span class = "boring" > pub fn find_kind_or_cause< U: StdError + 'static> (& self) -> Option< & U> {
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< / span > < span class = "boring" > self.iter()
< / span > < span class = "boring" > .filter_map(|e| {
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< / span > < span class = "boring" > e.downcast_ref::< Error< U> > ()
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< / span > < span class = "boring" > .map(|e| e.kind())
< / span > < span class = "boring" > .or_else(|| e.downcast_ref::< U> ())
< / span > < span class = "boring" > })
< / span > < span class = "boring" > .next()
< / span > < span class = "boring" > }
< / span > < span class = "boring" >
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< / span > < span class = "boring" > /// Return a reference to T of [`Error< T> `](Error)
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< / span > < span class = "boring" > ///
< / span > < span class = "boring" > /// # Examples
< / span > < span class = "boring" > ///
< / span > < span class = "boring" > /// ```rust
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< / span > < span class = "boring" > /// use chainerror::Context as _;
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< / span > < span class = "boring" > /// use std::error::Error;
< / span > < span class = "boring" > /// use std::io;
< / span > < span class = "boring" > ///
< / span > < span class = "boring" > /// fn do_some_io() -> Result< (), Box< dyn Error + Send + Sync> > {
< / span > < span class = "boring" > /// Err(io::Error::from(io::ErrorKind::NotFound))?;
< / span > < span class = "boring" > /// Ok(())
< / span > < span class = "boring" > /// }
< / span > < span class = "boring" > ///
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< / span > < span class = "boring" > /// chainerror::str_context!(Func2Error);
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< / span > < span class = "boring" > ///
< / span > < span class = "boring" > /// fn func2() -> Result< (), Box< dyn Error + Send + Sync> > {
< / span > < span class = "boring" > /// let filename = " foo.txt" ;
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< / span > < span class = "boring" > /// do_some_io().context(Func2Error(format!(" Error reading '{}'" , filename)))?;
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< / span > < span class = "boring" > /// Ok(())
< / span > < span class = "boring" > /// }
< / span > < span class = "boring" > ///
< / span > < span class = "boring" > /// #[derive(Debug)]
< / span > < span class = "boring" > /// enum Func1ErrorKind {
< / span > < span class = "boring" > /// Func2,
< / span > < span class = "boring" > /// IO(String),
< / span > < span class = "boring" > /// }
< / span > < span class = "boring" > ///
< / span > < span class = "boring" > /// /// impl ::std::fmt::Display for Func1ErrorKind {…}
< / span > < span class = "boring" > /// # impl ::std::fmt::Display for Func1ErrorKind {
< / span > < span class = "boring" > /// # fn fmt(& self, f: & mut ::std::fmt::Formatter) -> ::std::fmt::Result {
< / span > < span class = "boring" > /// # match self {
< / span > < span class = "boring" > /// # Func1ErrorKind::Func2 => write!(f, " func1 error calling func2" ),
< / span > < span class = "boring" > /// # Func1ErrorKind::IO(filename) => write!(f, " Error reading '{}'" , filename),
< / span > < span class = "boring" > /// # }
< / span > < span class = "boring" > /// # }
< / span > < span class = "boring" > /// # }
< / span > < span class = "boring" > ///
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< / span > < span class = "boring" > /// fn func1() -> chainerror::Result< (), Func1ErrorKind> {
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< / span > < span class = "boring" > /// func2().context(Func1ErrorKind::Func2)?;
< / span > < span class = "boring" > /// do_some_io().context(Func1ErrorKind::IO(" bar.txt" .into()))?;
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< / span > < span class = "boring" > /// Ok(())
< / span > < span class = "boring" > /// }
< / span > < span class = "boring" > ///
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< / span > < span class = "boring" > /// if let Err(e) = func1() {
< / span > < span class = "boring" > /// match e.kind() {
< / span > < span class = "boring" > /// Func1ErrorKind::Func2 => {}
< / span > < span class = "boring" > /// Func1ErrorKind::IO(filename) => panic!(),
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< / span > < span class = "boring" > /// }
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< / span > < span class = "boring" > /// }
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< / span > < span class = "boring" > /// # else {
< / span > < span class = "boring" > /// # unreachable!();
< / span > < span class = "boring" > /// # }
< / span > < span class = "boring" > /// ```
< / span > < span class = "boring" > #[inline]
< / span > < span class = "boring" > pub fn kind(& self) -> & T {
< / span > < span class = "boring" > & self.kind
< / span > < span class = "boring" > }
< / span > < span class = "boring" >
< / span > < span class = "boring" > /// Returns an Iterator over all error causes/sources
< / span > < span class = "boring" > ///
< / span > < span class = "boring" > /// # Example
< / span > < span class = "boring" > #[inline]
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< / span > < span class = "boring" > pub fn iter(& self) -> impl Iterator< Item = & (dyn StdError + 'static)> {
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< / span > < span class = "boring" > ErrorIter {
< / span > < span class = "boring" > current: Some(self),
< / span > < span class = "boring" > }
< / span > < span class = "boring" > }
< / span > < span class = "boring" > }
< / span > < span class = "boring" >
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< / span > < span class = "boring" > /// Convenience methods for `Result< > ` to turn the error into a decorated [`Error`](Error)
< / span > < span class = "boring" > pub trait Context< O, E: Into< Box< dyn StdError + 'static + Send + Sync> > > {
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< / span > < span class = "boring" > /// Decorate the error with a `kind` of type `T` and the source `Location`
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< / span > < span class = "boring" > fn context< T: 'static + Display + Debug> (self, kind: T) -> std::result::Result< O, Error< T> > ;
< / span > < span class = "boring" >
< / span > < span class = "boring" > /// Decorate the error just with the source `Location`
< / span > < span class = "boring" > fn annotate(self) -> std::result::Result< O, Error< AnnotatedError> > ;
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< / span > < span class = "boring" >
< / span > < span class = "boring" > /// Decorate the `error` with a `kind` of type `T` produced with a `FnOnce(& error)` and the source `Location`
< / span > < span class = "boring" > fn map_context< T: 'static + Display + Debug, F: FnOnce(& E) -> T> (
< / span > < span class = "boring" > self,
< / span > < span class = "boring" > op: F,
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< / span > < span class = "boring" > ) -> std::result::Result< O, Error< T> > ;
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< / span > < span class = "boring" > }
< / span > < span class = "boring" >
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< / span > < span class = "boring" > /// Convenience type to just decorate the error with the source `Location`
< / span > < span class = "boring" > pub struct AnnotatedError(());
< / span > < span class = "boring" >
< / span > < span class = "boring" > impl Display for AnnotatedError {
< / span > < span class = "boring" > fn fmt(& self, f: & mut Formatter< '_> ) -> std::fmt::Result {
< / span > < span class = "boring" > write!(f, " (passed error)" )
< / span > < span class = "boring" > }
< / span > < span class = "boring" > }
< / span > < span class = "boring" >
< / span > < span class = "boring" > impl Debug for AnnotatedError {
< / span > < span class = "boring" > fn fmt(& self, f: & mut Formatter< '_> ) -> std::fmt::Result {
< / span > < span class = "boring" > write!(f, " (passed error)" )
< / span > < span class = "boring" > }
< / span > < span class = "boring" > }
< / span > < span class = "boring" >
< / span > < span class = "boring" > impl< O, E: Into< Box< dyn StdError + 'static + Send + Sync> > > Context< O, E>
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< / span > < span class = "boring" > for std::result::Result< O, E>
< / span > < span class = "boring" > {
< / span > < span class = "boring" > #[track_caller]
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< / span > < span class = "boring" > #[inline]
< / span > < span class = "boring" > fn context< T: 'static + Display + Debug> (self, kind: T) -> std::result::Result< O, Error< T> > {
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< / span > < span class = "boring" > match self {
< / span > < span class = "boring" > Ok(t) => Ok(t),
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< / span > < span class = "boring" > Err(error_cause) => Err(Error::new(
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< / span > < span class = "boring" > kind,
< / span > < span class = "boring" > Some(error_cause.into()),
< / span > < span class = "boring" > Some(Location::caller().to_string()),
< / span > < span class = "boring" > )),
< / span > < span class = "boring" > }
< / span > < span class = "boring" > }
< / span > < span class = "boring" >
< / span > < span class = "boring" > #[track_caller]
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< / span > < span class = "boring" > #[inline]
< / span > < span class = "boring" > fn annotate(self) -> std::result::Result< O, Error< AnnotatedError> > {
< / span > < span class = "boring" > match self {
< / span > < span class = "boring" > Ok(t) => Ok(t),
< / span > < span class = "boring" > Err(error_cause) => Err(Error::new(
< / span > < span class = "boring" > AnnotatedError(()),
< / span > < span class = "boring" > Some(error_cause.into()),
< / span > < span class = "boring" > Some(Location::caller().to_string()),
< / span > < span class = "boring" > )),
< / span > < span class = "boring" > }
< / span > < span class = "boring" > }
< / span > < span class = "boring" >
< / span > < span class = "boring" > #[track_caller]
< / span > < span class = "boring" > #[inline]
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< / span > < span class = "boring" > fn map_context< T: 'static + Display + Debug, F: FnOnce(& E) -> T> (
< / span > < span class = "boring" > self,
< / span > < span class = "boring" > op: F,
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< / span > < span class = "boring" > ) -> std::result::Result< O, Error< T> > {
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< / span > < span class = "boring" > match self {
< / span > < span class = "boring" > Ok(t) => Ok(t),
< / span > < span class = "boring" > Err(error_cause) => {
< / span > < span class = "boring" > let kind = op(& error_cause);
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< / span > < span class = "boring" > Err(Error::new(
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< / span > < span class = "boring" > kind,
< / span > < span class = "boring" > Some(error_cause.into()),
< / span > < span class = "boring" > Some(Location::caller().to_string()),
< / span > < span class = "boring" > ))
< / span > < span class = "boring" > }
< / span > < span class = "boring" > }
< / span > < span class = "boring" > }
< / span > < span class = "boring" > }
< / span > < span class = "boring" >
< / span > < span class = "boring" > /// An iterator over all error causes/sources
< / span > < span class = "boring" > pub struct ErrorIter< 'a> {
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< / span > < span class = "boring" > current: Option< & 'a (dyn StdError + 'static)> ,
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< / span > < span class = "boring" > }
< / span > < span class = "boring" >
< / span > < span class = "boring" > impl< 'a> Iterator for ErrorIter< 'a> {
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< / span > < span class = "boring" > type Item = & 'a (dyn StdError + 'static);
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< / span > < span class = "boring" >
< / span > < span class = "boring" > #[inline]
< / span > < span class = "boring" > fn next(& mut self) -> Option< Self::Item> {
< / span > < span class = "boring" > let current = self.current;
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< / span > < span class = "boring" > self.current = self.current.and_then(StdError::source);
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< / span > < span class = "boring" > current
< / span > < span class = "boring" > }
< / span > < span class = "boring" > }
< / span > < span class = "boring" >
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< / span > < span class = "boring" > impl< T: 'static + Display + Debug> std::ops::Deref for Error< T> {
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< / span > < span class = "boring" > type Target = T;
< / span > < span class = "boring" >
< / span > < span class = "boring" > #[inline]
< / span > < span class = "boring" > fn deref(& self) -> & Self::Target {
< / span > < span class = "boring" > & self.kind
< / span > < span class = "boring" > }
< / span > < span class = "boring" > }
< / span > < span class = "boring" >
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< / span > < span class = "boring" > /// Convenience trait to hide the [`Error< T> `](Error) implementation internals
< / span > < span class = "boring" > pub trait ErrorDown {
< / span > < span class = "boring" > /// Test if of type `Error< T> `
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< / span > < span class = "boring" > fn is_chain< T: 'static + Display + Debug> (& self) -> bool;
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< / span > < span class = "boring" > /// Downcast to a reference of `Error< T> `
< / span > < span class = "boring" > fn downcast_chain_ref< T: 'static + Display + Debug> (& self) -> Option< & Error< T> > ;
< / span > < span class = "boring" > /// Downcast to a mutable reference of `Error< T> `
< / span > < span class = "boring" > fn downcast_chain_mut< T: 'static + Display + Debug> (& mut self) -> Option< & mut Error< T> > ;
< / span > < span class = "boring" > /// Downcast to T of `Error< T> `
< / span > < span class = "boring" > fn downcast_inner_ref< T: 'static + StdError> (& self) -> Option< & T> ;
< / span > < span class = "boring" > /// Downcast to T mutable reference of `Error< T> `
< / span > < span class = "boring" > fn downcast_inner_mut< T: 'static + StdError> (& mut self) -> Option< & mut T> ;
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< / span > < span class = "boring" > }
< / span > < span class = "boring" >
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< / span > < span class = "boring" > impl< U: 'static + Display + Debug> ErrorDown for Error< U> {
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< / span > < span class = "boring" > #[inline]
< / span > < span class = "boring" > fn is_chain< T: 'static + Display + Debug> (& self) -> bool {
< / span > < span class = "boring" > TypeId::of::< T> () == TypeId::of::< U> ()
< / span > < span class = "boring" > }
< / span > < span class = "boring" >
< / span > < span class = "boring" > #[inline]
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< / span > < span class = "boring" > fn downcast_chain_ref< T: 'static + Display + Debug> (& self) -> Option< & Error< T> > {
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< / span > < span class = "boring" > if self.is_chain::< T> () {
< / span > < span class = "boring" > #[allow(clippy::cast_ptr_alignment)]
< / span > < span class = "boring" > unsafe {
< / span > < span class = "boring" > #[allow(trivial_casts)]
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< / span > < span class = "boring" > Some(*(self as *const dyn StdError as *const & Error< T> ))
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< / span > < span class = "boring" > }
< / span > < span class = "boring" > } else {
< / span > < span class = "boring" > None
< / span > < span class = "boring" > }
< / span > < span class = "boring" > }
< / span > < span class = "boring" >
< / span > < span class = "boring" > #[inline]
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< / span > < span class = "boring" > fn downcast_chain_mut< T: 'static + Display + Debug> (& mut self) -> Option< & mut Error< T> > {
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< / span > < span class = "boring" > if self.is_chain::< T> () {
< / span > < span class = "boring" > #[allow(clippy::cast_ptr_alignment)]
< / span > < span class = "boring" > unsafe {
< / span > < span class = "boring" > #[allow(trivial_casts)]
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< / span > < span class = "boring" > Some(& mut *(self as *mut dyn StdError as *mut & mut Error< T> ))
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< / span > < span class = "boring" > }
< / span > < span class = "boring" > } else {
< / span > < span class = "boring" > None
< / span > < span class = "boring" > }
< / span > < span class = "boring" > }
< / span > < span class = "boring" > #[inline]
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< / span > < span class = "boring" > fn downcast_inner_ref< T: 'static + StdError> (& self) -> Option< & T> {
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< / span > < span class = "boring" > if self.is_chain::< T> () {
< / span > < span class = "boring" > #[allow(clippy::cast_ptr_alignment)]
< / span > < span class = "boring" > unsafe {
< / span > < span class = "boring" > #[allow(trivial_casts)]
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< / span > < span class = "boring" > Some(& (*(self as *const dyn StdError as *const & Error< T> )).kind)
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< / span > < span class = "boring" > }
< / span > < span class = "boring" > } else {
< / span > < span class = "boring" > None
< / span > < span class = "boring" > }
< / span > < span class = "boring" > }
< / span > < span class = "boring" >
< / span > < span class = "boring" > #[inline]
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< / span > < span class = "boring" > fn downcast_inner_mut< T: 'static + StdError> (& mut self) -> Option< & mut T> {
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< / span > < span class = "boring" > if self.is_chain::< T> () {
< / span > < span class = "boring" > #[allow(clippy::cast_ptr_alignment)]
< / span > < span class = "boring" > unsafe {
< / span > < span class = "boring" > #[allow(trivial_casts)]
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< / span > < span class = "boring" > Some(& mut (*(self as *mut dyn StdError as *mut & mut Error< T> )).kind)
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< / span > < span class = "boring" > }
< / span > < span class = "boring" > } else {
< / span > < span class = "boring" > None
< / span > < span class = "boring" > }
< / span > < span class = "boring" > }
< / span > < span class = "boring" > }
< / span > < span class = "boring" >
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< / span > < span class = "boring" > impl ErrorDown for dyn StdError + 'static {
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< / span > < span class = "boring" > #[inline]
< / span > < span class = "boring" > fn is_chain< T: 'static + Display + Debug> (& self) -> bool {
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< / span > < span class = "boring" > self.is::< Error< T> > ()
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< / span > < span class = "boring" > }
< / span > < span class = "boring" >
< / span > < span class = "boring" > #[inline]
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< / span > < span class = "boring" > fn downcast_chain_ref< T: 'static + Display + Debug> (& self) -> Option< & Error< T> > {
< / span > < span class = "boring" > self.downcast_ref::< Error< T> > ()
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< / span > < span class = "boring" > }
< / span > < span class = "boring" >
< / span > < span class = "boring" > #[inline]
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< / span > < span class = "boring" > fn downcast_chain_mut< T: 'static + Display + Debug> (& mut self) -> Option< & mut Error< T> > {
< / span > < span class = "boring" > self.downcast_mut::< Error< T> > ()
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< / span > < span class = "boring" > }
< / span > < span class = "boring" >
< / span > < span class = "boring" > #[inline]
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< / span > < span class = "boring" > fn downcast_inner_ref< T: 'static + StdError> (& self) -> Option< & T> {
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< / span > < span class = "boring" > self.downcast_ref::< T> ()
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< / span > < span class = "boring" > .or_else(|| self.downcast_ref::< Error< T> > ().map(|e| e.kind()))
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< / span > < span class = "boring" > }
< / span > < span class = "boring" >
< / span > < span class = "boring" > #[inline]
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< / span > < span class = "boring" > fn downcast_inner_mut< T: 'static + StdError> (& mut self) -> Option< & mut T> {
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< / span > < span class = "boring" > if self.is::< T> () {
< / span > < span class = "boring" > return self.downcast_mut::< T> ();
< / span > < span class = "boring" > }
< / span > < span class = "boring" >
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< / span > < span class = "boring" > self.downcast_mut::< Error< T> > ()
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< / span > < span class = "boring" > .and_then(|e| e.downcast_inner_mut::< T> ())
< / span > < span class = "boring" > }
< / span > < span class = "boring" > }
< / span > < span class = "boring" >
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< / span > < span class = "boring" > impl ErrorDown for dyn StdError + 'static + Send {
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< / span > < span class = "boring" > #[inline]
< / span > < span class = "boring" > fn is_chain< T: 'static + Display + Debug> (& self) -> bool {
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< / span > < span class = "boring" > self.is::< Error< T> > ()
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< / span > < span class = "boring" > }
< / span > < span class = "boring" >
< / span > < span class = "boring" > #[inline]
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< / span > < span class = "boring" > fn downcast_chain_ref< T: 'static + Display + Debug> (& self) -> Option< & Error< T> > {
< / span > < span class = "boring" > self.downcast_ref::< Error< T> > ()
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< / span > < span class = "boring" > }
< / span > < span class = "boring" >
< / span > < span class = "boring" > #[inline]
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< / span > < span class = "boring" > fn downcast_chain_mut< T: 'static + Display + Debug> (& mut self) -> Option< & mut Error< T> > {
< / span > < span class = "boring" > self.downcast_mut::< Error< T> > ()
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< / span > < span class = "boring" > }
< / span > < span class = "boring" >
< / span > < span class = "boring" > #[inline]
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< / span > < span class = "boring" > fn downcast_inner_ref< T: 'static + StdError> (& self) -> Option< & T> {
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< / span > < span class = "boring" > self.downcast_ref::< T> ()
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< / span > < span class = "boring" > .or_else(|| self.downcast_ref::< Error< T> > ().map(|e| e.kind()))
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< / span > < span class = "boring" > }
< / span > < span class = "boring" >
< / span > < span class = "boring" > #[inline]
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< / span > < span class = "boring" > fn downcast_inner_mut< T: 'static + StdError> (& mut self) -> Option< & mut T> {
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< / span > < span class = "boring" > if self.is::< T> () {
< / span > < span class = "boring" > return self.downcast_mut::< T> ();
< / span > < span class = "boring" > }
< / span > < span class = "boring" >
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< / span > < span class = "boring" > self.downcast_mut::< Error< T> > ()
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< / span > < span class = "boring" > .and_then(|e| e.downcast_inner_mut::< T> ())
< / span > < span class = "boring" > }
< / span > < span class = "boring" > }
< / span > < span class = "boring" >
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< / span > < span class = "boring" > impl ErrorDown for dyn StdError + 'static + Send + Sync {
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< / span > < span class = "boring" > #[inline]
< / span > < span class = "boring" > fn is_chain< T: 'static + Display + Debug> (& self) -> bool {
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< / span > < span class = "boring" > self.is::< Error< T> > ()
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< / span > < span class = "boring" > }
< / span > < span class = "boring" >
< / span > < span class = "boring" > #[inline]
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< / span > < span class = "boring" > fn downcast_chain_ref< T: 'static + Display + Debug> (& self) -> Option< & Error< T> > {
< / span > < span class = "boring" > self.downcast_ref::< Error< T> > ()
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< / span > < span class = "boring" > }
< / span > < span class = "boring" >
< / span > < span class = "boring" > #[inline]
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< / span > < span class = "boring" > fn downcast_chain_mut< T: 'static + Display + Debug> (& mut self) -> Option< & mut Error< T> > {
< / span > < span class = "boring" > self.downcast_mut::< Error< T> > ()
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< / span > < span class = "boring" > }
< / span > < span class = "boring" >
< / span > < span class = "boring" > #[inline]
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< / span > < span class = "boring" > fn downcast_inner_ref< T: 'static + StdError> (& self) -> Option< & T> {
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< / span > < span class = "boring" > self.downcast_ref::< T> ()
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< / span > < span class = "boring" > .or_else(|| self.downcast_ref::< Error< T> > ().map(|e| e.kind()))
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< / span > < span class = "boring" > }
< / span > < span class = "boring" >
< / span > < span class = "boring" > #[inline]
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< / span > < span class = "boring" > fn downcast_inner_mut< T: 'static + StdError> (& mut self) -> Option< & mut T> {
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< / span > < span class = "boring" > if self.is::< T> () {
< / span > < span class = "boring" > return self.downcast_mut::< T> ();
< / span > < span class = "boring" > }
< / span > < span class = "boring" >
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< / span > < span class = "boring" > self.downcast_mut::< Error< T> > ()
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< / span > < span class = "boring" > .and_then(|e| e.downcast_inner_mut::< T> ())
< / span > < span class = "boring" > }
< / span > < span class = "boring" > }
< / span > < span class = "boring" >
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< / span > < span class = "boring" > impl< T: 'static + Display + Debug> StdError for Error< T> {
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< / span > < span class = "boring" > #[inline]
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< / span > < span class = "boring" > fn source(& self) -> Option< & (dyn StdError + 'static)> {
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< / span > < span class = "boring" > self.error_cause
< / span > < span class = "boring" > .as_ref()
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< / span > < span class = "boring" > .map(|e| e.as_ref() as & (dyn StdError + 'static))
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< / span > < span class = "boring" > }
< / span > < span class = "boring" > }
< / span > < span class = "boring" >
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< / span > < span class = "boring" > impl< T: 'static + Display + Debug> StdError for & mut Error< T> {
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< / span > < span class = "boring" > #[inline]
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< / span > < span class = "boring" > fn source(& self) -> Option< & (dyn StdError + 'static)> {
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< / span > < span class = "boring" > self.error_cause
< / span > < span class = "boring" > .as_ref()
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< / span > < span class = "boring" > .map(|e| e.as_ref() as & (dyn StdError + 'static))
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< / span > < span class = "boring" > }
< / span > < span class = "boring" > }
< / span > < span class = "boring" >
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< / span > < span class = "boring" > impl< T: 'static + Display + Debug> Display for Error< T> {
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< / span > < span class = "boring" > #[inline]
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< / span > < span class = "boring" > fn fmt(& self, f: & mut Formatter< '_> ) -> std::fmt::Result {
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< / span > < span class = "boring" > write!(f, " {}" , self.kind)?;
< / span > < span class = "boring" >
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< / span > < span class = "boring" > if f.alternate() {
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< / span > < span class = "boring" > if let Some(e) = self.source() {
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< / span > < span class = "boring" > write!(f, " \nCaused by:\n {:#}" , & e)?;
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< / span > < span class = "boring" > }
< / span > < span class = "boring" > }
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< / span > < span class = "boring" >
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< / span > < span class = "boring" > Ok(())
< / span > < span class = "boring" > }
< / span > < span class = "boring" > }
< / span > < span class = "boring" >
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< / span > < span class = "boring" > impl< T: 'static + Display + Debug> Debug for Error< T> {
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< / span > < span class = "boring" > #[inline]
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< / span > < span class = "boring" > fn fmt(& self, f: & mut Formatter< '_> ) -> std::fmt::Result {
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< / span > < span class = "boring" > if f.alternate() {
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< / span > < span class = "boring" > let mut f = f.debug_struct(& format!(" Error< {}> " , std::any::type_name::< T> ()));
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< / span > < span class = "boring" >
< / span > < span class = "boring" > let f = f
< / span > < span class = "boring" > .field(" occurrence" , & self.occurrence)
< / span > < span class = "boring" > .field(" kind" , & self.kind)
< / span > < span class = "boring" > .field(" source" , & self.source());
< / span > < span class = "boring" >
< / span > < span class = "boring" > f.finish()
< / span > < span class = "boring" > } else {
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< / span > < span class = "boring" > if let Some(ref o) = self.occurrence {
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< / span > < span class = "boring" > write!(f, " {}: " , o)?;
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< / span > < span class = "boring" > }
< / span > < span class = "boring" >
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< / span > < span class = "boring" > if TypeId::of::< String> () == TypeId::of::< T> ()
< / span > < span class = "boring" > || TypeId::of::< & str> () == TypeId::of::< T> ()
< / span > < span class = "boring" > {
< / span > < span class = "boring" > Display::fmt(& self.kind, f)?;
< / span > < span class = "boring" > } else {
< / span > < span class = "boring" > Debug::fmt(& self.kind, f)?;
< / span > < span class = "boring" > }
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< / span > < span class = "boring" >
< / span > < span class = "boring" > if let Some(e) = self.source() {
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< / span > < span class = "boring" > write!(f, " \nCaused by:\n{:?}" , & e)?;
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< / span > < span class = "boring" > }
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< / span > < span class = "boring" > Ok(())
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< / span > < span class = "boring" > }
< / span > < span class = "boring" > }
< / span > < span class = "boring" > }
< / span > < span class = "boring" >
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< / span > < span class = "boring" > impl< T> From< T> for Error< T>
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< / span > < span class = "boring" > where
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< / span > < span class = "boring" > T: 'static + Display + Debug,
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< / span > < span class = "boring" > {
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< / span > < span class = "boring" > #[track_caller]
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< / span > < span class = "boring" > #[inline]
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< / span > < span class = "boring" > fn from(e: T) -> Error< T> {
< / span > < span class = "boring" > Error::new(e, None, Some(Location::caller().to_string()))
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< / span > < span class = "boring" > }
< / span > < span class = "boring" > }
< / span > < span class = "boring" > /// Convenience macro to create a " new type" T(String) and implement Display + Debug for T
< / span > < span class = "boring" > ///
< / span > < span class = "boring" > /// # Examples
< / span > < span class = "boring" > ///
< / span > < span class = "boring" > /// ```rust
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< / span > < span class = "boring" > /// # use chainerror::Context as _;
< / span > < span class = "boring" > /// # use chainerror::ErrorDown as _;
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< / span > < span class = "boring" > /// # use std::error::Error;
< / span > < span class = "boring" > /// # use std::io;
< / span > < span class = "boring" > /// # use std::result::Result;
< / span > < span class = "boring" > /// # fn do_some_io() -> Result< (), Box< dyn Error + Send + Sync> > {
< / span > < span class = "boring" > /// # Err(io::Error::from(io::ErrorKind::NotFound))?;
< / span > < span class = "boring" > /// # Ok(())
< / span > < span class = "boring" > /// # }
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< / span > < span class = "boring" > /// chainerror::str_context!(Func2Error);
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< / span > < span class = "boring" > ///
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< / span > < span class = "boring" > /// fn func2() -> chainerror::Result< (), Func2Error> {
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< / span > < span class = "boring" > /// let filename = " foo.txt" ;
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< / span > < span class = "boring" > /// do_some_io().context(Func2Error(format!(" Error reading '{}'" , filename)))?;
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< / span > < span class = "boring" > /// Ok(())
< / span > < span class = "boring" > /// }
< / span > < span class = "boring" > ///
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< / span > < span class = "boring" > /// chainerror::str_context!(Func1Error);
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< / span > < span class = "boring" > ///
< / span > < span class = "boring" > /// fn func1() -> Result< (), Box< dyn Error> > {
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< / span > < span class = "boring" > /// func2().context(Func1Error::new(" func1 error" ))?;
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< / span > < span class = "boring" > /// Ok(())
< / span > < span class = "boring" > /// }
< / span > < span class = "boring" > /// # if let Err(e) = func1() {
< / span > < span class = "boring" > /// # if let Some(f1err) = e.downcast_chain_ref::< Func1Error> () {
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< / span > < span class = "boring" > /// # assert!(f1err.find_cause::< chainerror::Error< Func2Error> > ().is_some());
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< / span > < span class = "boring" > /// # assert!(f1err.find_chain_cause::< Func2Error> ().is_some());
< / span > < span class = "boring" > /// # } else {
< / span > < span class = "boring" > /// # panic!();
< / span > < span class = "boring" > /// # }
< / span > < span class = "boring" > /// # } else {
< / span > < span class = "boring" > /// # unreachable!();
< / span > < span class = "boring" > /// # }
< / span > < span class = "boring" > /// ```
< / span > < span class = "boring" > #[macro_export]
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< / span > < span class = "boring" > macro_rules! str_context {
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< / span > < span class = "boring" > ($e:ident) => {
< / span > < span class = "boring" > #[derive(Clone)]
< / span > < span class = "boring" > pub struct $e(pub String);
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< / span > < span class = "boring" > impl $e {
< / span > < span class = "boring" > pub fn new< S: Into< String> > (s: S) -> Self {
< / span > < span class = "boring" > $e(s.into())
< / span > < span class = "boring" > }
< / span > < span class = "boring" > }
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< / span > < span class = "boring" > impl ::std::fmt::Display for $e {
< / span > < span class = "boring" > fn fmt(& self, f: & mut ::std::fmt::Formatter) -> ::std::fmt::Result {
< / span > < span class = "boring" > write!(f, " {}" , self.0)
< / span > < span class = "boring" > }
< / span > < span class = "boring" > }
< / span > < span class = "boring" > impl ::std::fmt::Debug for $e {
< / span > < span class = "boring" > fn fmt(& self, f: & mut ::std::fmt::Formatter) -> ::std::fmt::Result {
< / span > < span class = "boring" > write!(f, " {}({})" , stringify!($e), self.0)
< / span > < span class = "boring" > }
< / span > < span class = "boring" > }
< / span > < span class = "boring" > impl ::std::error::Error for $e {}
< / span > < span class = "boring" > };
< / span > < span class = "boring" > }
< / span > < span class = "boring" >
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< / span > < span class = "boring" > /// Derive an Error for an ErrorKind, which wraps a [`Error`](Error) and implements a `kind()` method
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< / span > < span class = "boring" > ///
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< / span > < span class = "boring" > /// It basically hides [`Error`](Error) to the outside and only exposes the [`kind()`](Error::kind)
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< / span > < span class = "boring" > /// method.
< / span > < span class = "boring" > ///
< / span > < span class = "boring" > /// Error::kind() returns the ErrorKind
< / span > < span class = "boring" > /// Error::source() returns the parent error
< / span > < span class = "boring" > ///
< / span > < span class = "boring" > /// # Examples
< / span > < span class = "boring" > ///
< / span > < span class = "boring" > /// ```rust
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< / span > < span class = "boring" > /// use chainerror::Context as _;
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< / span > < span class = "boring" > /// use std::io;
< / span > < span class = "boring" > ///
< / span > < span class = "boring" > /// fn do_some_io(_f: & str) -> std::result::Result< (), io::Error> {
< / span > < span class = "boring" > /// return Err(io::Error::from(io::ErrorKind::NotFound));
< / span > < span class = "boring" > /// }
< / span > < span class = "boring" > ///
< / span > < span class = "boring" > /// #[derive(Debug, Clone)]
< / span > < span class = "boring" > /// pub enum ErrorKind {
< / span > < span class = "boring" > /// IO(String),
< / span > < span class = "boring" > /// FatalError(String),
< / span > < span class = "boring" > /// Unknown,
< / span > < span class = "boring" > /// }
< / span > < span class = "boring" > ///
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< / span > < span class = "boring" > /// chainerror::err_kind!(Error, ErrorKind);
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< / span > < span class = "boring" > ///
< / span > < span class = "boring" > /// impl std::fmt::Display for ErrorKind {
< / span > < span class = "boring" > /// fn fmt(& self, f: & mut ::std::fmt::Formatter) -> std::fmt::Result {
< / span > < span class = "boring" > /// match self {
< / span > < span class = "boring" > /// ErrorKind::FatalError(e) => write!(f, " fatal error {}" , e),
< / span > < span class = "boring" > /// ErrorKind::Unknown => write!(f, " unknown error" ),
< / span > < span class = "boring" > /// ErrorKind::IO(filename) => write!(f, " Error reading '{}'" , filename),
< / span > < span class = "boring" > /// }
< / span > < span class = "boring" > /// }
< / span > < span class = "boring" > /// }
< / span > < span class = "boring" > ///
< / span > < span class = "boring" > /// impl ErrorKind {
< / span > < span class = "boring" > /// fn from_io_error(e: & io::Error, f: String) -> Self {
< / span > < span class = "boring" > /// match e.kind() {
< / span > < span class = "boring" > /// io::ErrorKind::BrokenPipe => panic!(" Should not happen" ),
< / span > < span class = "boring" > /// io::ErrorKind::ConnectionReset => {
< / span > < span class = "boring" > /// ErrorKind::FatalError(format!(" While reading `{}`: {}" , f, e))
< / span > < span class = "boring" > /// }
< / span > < span class = "boring" > /// _ => ErrorKind::IO(f),
< / span > < span class = "boring" > /// }
< / span > < span class = "boring" > /// }
< / span > < span class = "boring" > /// }
< / span > < span class = "boring" > ///
< / span > < span class = "boring" > /// impl From< & io::Error> for ErrorKind {
< / span > < span class = "boring" > /// fn from(e: & io::Error) -> Self {
< / span > < span class = "boring" > /// ErrorKind::IO(format!(" {}" , e))
< / span > < span class = "boring" > /// }
< / span > < span class = "boring" > /// }
< / span > < span class = "boring" > ///
< / span > < span class = "boring" > /// pub fn func1() -> std::result::Result< (), Error> {
< / span > < span class = "boring" > /// let filename = " bar.txt" ;
< / span > < span class = "boring" > ///
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< / span > < span class = "boring" > /// do_some_io(filename).map_context(|e| ErrorKind::from_io_error(e, filename.into()))?;
< / span > < span class = "boring" > /// do_some_io(filename).map_context(|e| ErrorKind::IO(filename.into()))?;
< / span > < span class = "boring" > /// do_some_io(filename).map_context(|e| ErrorKind::from(e))?;
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< / span > < span class = "boring" > /// Ok(())
< / span > < span class = "boring" > /// }
< / span > < span class = "boring" > /// ```
< / span > < span class = "boring" > #[macro_export]
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< / span > < span class = "boring" > macro_rules! err_kind {
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< / span > < span class = "boring" > ($e:ident, $k:ident) => {
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< / span > < span class = "boring" > pub struct $e($crate::Error< $k> );
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< / span > < span class = "boring" >
< / span > < span class = "boring" > impl $e {
< / span > < span class = "boring" > pub fn kind(& self) -> & $k {
< / span > < span class = "boring" > self.0.kind()
< / span > < span class = "boring" > }
< / span > < span class = "boring" > }
< / span > < span class = "boring" >
< / span > < span class = "boring" > impl From< $k> for $e {
< / span > < span class = "boring" > fn from(e: $k) -> Self {
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< / span > < span class = "boring" > $e($crate::Error::new(e, None, None))
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< / span > < span class = "boring" > }
< / span > < span class = "boring" > }
< / span > < span class = "boring" >
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< / span > < span class = "boring" > impl From< $crate::Error< $k> > for $e {
< / span > < span class = "boring" > fn from(e: $crate::Error< $k> ) -> Self {
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< / span > < span class = "boring" > $e(e)
< / span > < span class = "boring" > }
< / span > < span class = "boring" > }
< / span > < span class = "boring" >
< / span > < span class = "boring" > impl From< & $e> for $k
< / span > < span class = "boring" > where
< / span > < span class = "boring" > $k: Clone,
< / span > < span class = "boring" > {
< / span > < span class = "boring" > fn from(e: & $e) -> Self {
< / span > < span class = "boring" > e.kind().clone()
< / span > < span class = "boring" > }
< / span > < span class = "boring" > }
< / span > < span class = "boring" >
< / span > < span class = "boring" > impl std::error::Error for $e {
< / span > < span class = "boring" > fn source(& self) -> Option< & (dyn std::error::Error + 'static)> {
< / span > < span class = "boring" > self.0.source()
< / span > < span class = "boring" > }
< / span > < span class = "boring" > }
< / span > < span class = "boring" >
< / span > < span class = "boring" > impl std::fmt::Display for $e {
< / span > < span class = "boring" > fn fmt(& self, f: & mut std::fmt::Formatter) -> std::fmt::Result {
< / span > < span class = "boring" > std::fmt::Display::fmt(& self.0, f)
< / span > < span class = "boring" > }
< / span > < span class = "boring" > }
< / span > < span class = "boring" >
< / span > < span class = "boring" > impl std::fmt::Debug for $e {
< / span > < span class = "boring" > fn fmt(& self, f: & mut std::fmt::Formatter) -> std::fmt::Result {
< / span > < span class = "boring" > std::fmt::Debug::fmt(& self.0, f)
< / span > < span class = "boring" > }
< / span > < span class = "boring" > }
< / span > < span class = "boring" > };
< / span > < span class = "boring" > }
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< / span > < span class = "boring" > }< / span > < / code > < / pre > < / pre >
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< / main >
< nav class = "nav-wrapper" aria-label = "Page navigation" >
<!-- Mobile navigation buttons -->
< a rel = "prev" href = "tutorial6.html" class = "mobile-nav-chapters previous" title = "Previous chapter" aria-label = "Previous chapter" aria-keyshortcuts = "Left" >
< i class = "fa fa-angle-left" > < / i >
< / a >
< a rel = "next" href = "tutorial8.html" class = "mobile-nav-chapters next" title = "Next chapter" aria-label = "Next chapter" aria-keyshortcuts = "Right" >
< i class = "fa fa-angle-right" > < / i >
< / a >
< div style = "clear: both" > < / div >
< / nav >
< / div >
< / div >
< nav class = "nav-wide-wrapper" aria-label = "Page navigation" >
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< a rel = "prev" href = "tutorial6.html" class = "nav-chapters previous" title = "Previous chapter" aria-label = "Previous chapter" aria-keyshortcuts = "Left" >
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< i class = "fa fa-angle-left" > < / i >
< / a >
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< a rel = "next" href = "tutorial8.html" class = "nav-chapters next" title = "Next chapter" aria-label = "Next chapter" aria-keyshortcuts = "Right" >
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< i class = "fa fa-angle-right" > < / i >
< / a >
< / nav >
< / div >
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< script >
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window.playground_copyable = true;
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< / script >
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< script src = "elasticlunr.min.js" > < / script >
< script src = "mark.min.js" > < / script >
< script src = "searcher.js" > < / script >
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< script src = "clipboard.min.js" > < / script >
< script src = "highlight.js" > < / script >
< script src = "book.js" > < / script >
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<!-- Custom JS scripts -->
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< / div >
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< / body >
< / html >
