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<ol class="chapter"><li><a href="tutorial1.html"><strong aria-hidden="true">1.</strong> Chapter 1</a></li><li><a href="tutorial2.html"><strong aria-hidden="true">2.</strong> Chapter 2</a></li><li><a href="tutorial3.html"><strong aria-hidden="true">3.</strong> Chapter 3</a></li><li><a href="tutorial4.html"><strong aria-hidden="true">4.</strong> Chapter 4</a></li><li><a href="tutorial5.html"><strong aria-hidden="true">5.</strong> Chapter 5</a></li><li><a href="tutorial6.html"><strong aria-hidden="true">6.</strong> Chapter 6</a></li><li><a href="tutorial7.html"><strong aria-hidden="true">7.</strong> Chapter 7</a></li><li><a href="tutorial8.html"><strong aria-hidden="true">8.</strong> Chapter 8</a></li><li><a href="tutorial9.html"><strong aria-hidden="true">9.</strong> Chapter 9</a></li><li><a href="tutorial10.html"><strong aria-hidden="true">10.</strong> Chapter 10</a></li><li><a href="tutorial11.html"><strong aria-hidden="true">11.</strong> Chapter 11</a></li></ol>
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<h1 class="menu-title">chainerror</h1>
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<main>
<a class="header" href="#simple-string-errors" id="simple-string-errors"><h1>Simple String Errors</h1></a>
<p>The most simplest of doing error handling in rust is by returning <code>String</code> as a <code>Box<Error></code>.</p>
<p>As you can see by running the example (the "Play" button in upper right of the code block), this only
prints out the last <code>Error</code>.</p>
<p>If the rust <code>main</code> function returns an Err(), this Err() will be displayed with <code>std::fmt::Debug</code>.</p>
<pre><pre class="playpen"><code class="language-rust">use std::error::Error;
use std::result::Result;
fn do_some_io() -> Result<(), Box<Error>> {
Err("do_some_io error")?;
Ok(())
}
fn func2() -> Result<(), Box<Error>> {
if let Err(_) = do_some_io() {
Err("func2 error")?;
}
Ok(())
}
fn func1() -> Result<(), Box<Error>> {
if let Err(_) = func2() {
Err("func1 error")?;
}
Ok(())
}
fn main() -> Result<(), Box<Error>> {
func1()
}
</code></pre></pre>
<a class="header" href="#simple-chained-string-errors" id="simple-chained-string-errors"><h1>Simple Chained String Errors</h1></a>
<p>Now with the help of the <code>chainerror</code> crate, we can have a nicer output.</p>
<p>Press the play button in the upper right corner and see the nice debug output.</p>
<pre><pre class="playpen"><code class="language-rust">use crate::chainerror::*;
use std::error::Error;
use std::result::Result;
fn do_some_io() -> Result<(), Box<Error>> {
Err("do_some_io error")?;
Ok(())
}
fn func2() -> Result<(), Box<Error>> {
if let Err(e) = do_some_io() {
Err(cherr!(e, "func2 error"))?;
}
Ok(())
}
fn func1() -> Result<(), Box<Error>> {
if let Err(e) = func2() {
Err(cherr!(e, "func1 error"))?;
}
Ok(())
}
fn main() -> Result<(), Box<Error>> {
func1()
}
# #[allow(dead_code)]
# mod chainerror {
# use std::error::Error;
# use std::fmt::{Debug, Display, Formatter, Result};
# use std::result::Result as StdResult;
#
# pub struct ChainError<T> {
# #[cfg(not(feature = "no-fileline"))]
# occurrence: Option<(u32, &'static str)>,
# kind: T,
# error_cause: Option<Box<dyn Error + 'static>>,
# }
#
# pub type ChainResult<O, E> = StdResult<O, ChainError<E>>;
#
# impl<T: 'static + Display + Debug> ChainError<T> {
# #[cfg(not(feature = "no-fileline"))]
# pub fn new(
# kind: T,
# error_cause: Option<Box<dyn Error + 'static>>,
# occurrence: Option<(u32, &'static str)>,
# ) -> Self {
# Self {
# occurrence,
# kind,
# error_cause,
# }
# }
#
# #[cfg(feature = "no-fileline")]
# pub fn new(
# kind: T,
# error_cause: Option<Box<dyn Error + 'static>>,
# _occurrence: Option<(u32, &'static str)>,
# ) -> Self {
# Self { kind, error_cause }
# }
#
# pub fn root_cause(&self) -> Option<&(dyn Error + 'static)> {
# let mut cause = self as &(dyn Error + 'static);
# while let Some(c) = cause.source() {
# cause = c;
# }
# Some(cause)
# }
#
# pub fn find_cause<U: Error + 'static>(&self) -> Option<&U> {
# let mut cause = self as &(dyn Error + 'static);
# loop {
# if cause.is::<U>() {
# return cause.downcast_ref::<U>();
# }
#
# match cause.source() {
# Some(c) => cause = c,
# None => return None,
# }
# }
# }
#
# pub fn find_chain_cause<U: Error + 'static>(&self) -> Option<&ChainError<U>> {
# let mut cause = self as &(dyn Error + 'static);
# loop {
# if cause.is::<ChainError<U>>() {
# return cause.downcast_ref::<ChainError<U>>();
# }
#
# match cause.source() {
# Some(c) => cause = c,
# None => return None,
# }
# }
# }
#
# pub fn kind<'a>(&'a self) -> &'a T {
# &self.kind
# }
# }
#
# pub trait ChainErrorDown {
# fn is_chain<T: 'static + Display + Debug>(&self) -> bool;
# fn downcast_chain_ref<T: 'static + Display + Debug>(&self) -> Option<&ChainError<T>>;
# fn downcast_chain_mut<T: 'static + Display + Debug>(&mut self) -> Option<&mut ChainError<T>>;
# }
#
# use std::any::TypeId;
#
# impl<U: 'static + Display + Debug> ChainErrorDown for ChainError<U> {
# fn is_chain<T: 'static + Display + Debug>(&self) -> bool {
# TypeId::of::<T>() == TypeId::of::<U>()
# }
#
# fn downcast_chain_ref<T: 'static + Display + Debug>(&self) -> Option<&ChainError<T>> {
# if self.is_chain::<T>() {
# unsafe { Some(&*(self as *const dyn Error as *const &ChainError<T>)) }
# } else {
# None
# }
# }
#
# fn downcast_chain_mut<T: 'static + Display + Debug>(&mut self) -> Option<&mut ChainError<T>> {
# if self.is_chain::<T>() {
# unsafe { Some(&mut *(self as *mut dyn Error as *mut &mut ChainError<T>)) }
# } else {
# None
# }
# }
# }
#
# impl ChainErrorDown for dyn Error + 'static {
# fn is_chain<T: 'static + Display + Debug>(&self) -> bool {
# self.is::<ChainError<T>>()
# }
#
# fn downcast_chain_ref<T: 'static + Display + Debug>(&self) -> Option<&ChainError<T>> {
# self.downcast_ref::<ChainError<T>>()
# }
#
# fn downcast_chain_mut<T: 'static + Display + Debug>(&mut self) -> Option<&mut ChainError<T>> {
# self.downcast_mut::<ChainError<T>>()
# }
# }
#
# impl ChainErrorDown for dyn Error + 'static + Send {
# fn is_chain<T: 'static + Display + Debug>(&self) -> bool {
# self.is::<ChainError<T>>()
# }
#
# fn downcast_chain_ref<T: 'static + Display + Debug>(&self) -> Option<&ChainError<T>> {
# self.downcast_ref::<ChainError<T>>()
# }
#
# fn downcast_chain_mut<T: 'static + Display + Debug>(&mut self) -> Option<&mut ChainError<T>> {
# self.downcast_mut::<ChainError<T>>()
# }
# }
#
# impl ChainErrorDown for dyn Error + 'static + Send + Sync {
# fn is_chain<T: 'static + Display + Debug>(&self) -> bool {
# self.is::<ChainError<T>>()
# }
#
# fn downcast_chain_ref<T: 'static + Display + Debug>(&self) -> Option<&ChainError<T>> {
# self.downcast_ref::<ChainError<T>>()
# }
#
# fn downcast_chain_mut<T: 'static + Display + Debug>(&mut self) -> Option<&mut ChainError<T>> {
# self.downcast_mut::<ChainError<T>>()
# }
# }
#
# impl<T: 'static + Display + Debug> Error for ChainError<T> {
# fn source(&self) -> Option<&(dyn Error + 'static)> {
# if let Some(ref e) = self.error_cause {
# Some(e.as_ref())
# } else {
# None
# }
# }
# }
#
# impl<T: 'static + Display + Debug> Error for &ChainError<T> {
# fn source(&self) -> Option<&(dyn Error + 'static)> {
# if let Some(ref e) = self.error_cause {
# Some(e.as_ref())
# } else {
# None
# }
# }
# }
#
# impl<T: 'static + Display + Debug> Error for &mut ChainError<T> {
# fn source(&self) -> Option<&(dyn Error + 'static)> {
# if let Some(ref e) = self.error_cause {
# Some(e.as_ref())
# } else {
# None
# }
# }
# }
#
# impl<T: 'static + Display + Debug> Display for ChainError<T> {
# fn fmt(&self, f: &mut Formatter) -> Result {
# write!(f, "{}", self.kind)?;
#
# #[cfg(feature = "display-cause")]
# {
# if let Some(e) = self.source() {
# writeln!(f, "\nCaused by:")?;
# Display::fmt(&e, f)?;
# }
# }
# Ok(())
# }
# }
#
# impl<T: 'static + Display + Debug> Debug for ChainError<T> {
# fn fmt(&self, f: &mut Formatter) -> Result {
# #[cfg(not(feature = "no-fileline"))]
# {
# if let Some(o) = self.occurrence {
# write!(f, "{}:{}: ", o.1, o.0)?;
# }
# }
#
# Debug::fmt(&self.kind, f)?;
#
# #[cfg(not(feature = "no-debug-cause"))]
# {
# if let Some(e) = self.source() {
# writeln!(f, "\nCaused by:")?;
# Debug::fmt(&e, f)?;
# }
# }
# Ok(())
# }
# }
#
# #[macro_export]
# macro_rules! cherr {
# ( $k:expr ) => {
# ChainError::<_>::new($k, None, Some((line!(), file!())))
# };
# ( $e:expr, $k:expr ) => {
# ChainError::<_>::new($k, Some(Box::from($e)), Some((line!(), file!())))
# };
# }
#
# #[macro_export]
# macro_rules! mstrerr {
# ( $t:ident, $v:expr $(, $more:expr)* ) => {
# |e| cherr!(e, $t (format!($v, $( $more , )* )))
# };
# ( $t:path, $v:expr $(, $more:expr)* ) => {
# |e| cherr!(e, $t (format!($v, $( $more , )* )))
# };
# ( $v:expr $(, $more:expr)* ) => {
# |e| cherr!(e, format!($v, $( $more , )* ))
# };
# }
#
# #[macro_export]
# macro_rules! derive_str_cherr {
# ($e:ident) => {
# struct $e(String);
# impl ::std::fmt::Display for $e {
# fn fmt(&self, f: &mut ::std::fmt::Formatter) -> ::std::fmt::Result {
# write!(f, "{}", self.0)
# }
# }
# impl ::std::fmt::Debug for $e {
# fn fmt(&self, f: &mut ::std::fmt::Formatter) -> ::std::fmt::Result {
# write!(f, "{}({})", stringify!($e), self.0)
# }
# }
# impl ::std::error::Error for $e {}
# };
# }
#
# #[macro_export]
# macro_rules! try_cherr_ref {
# ( $e:expr, $t:ident ) => {
# $e.downcast_ref::<ChainError<$t>>()
# };
# ( $e:expr, $t:path ) => {
# $e.downcast_ref::<ChainError<$t>>()
# };
# }
#
# #[macro_export]
# macro_rules! try_cherr_mut {
# ( $e:expr, $t:ident ) => {
# $e.downcast_mut::<ChainError<$t>>()
# };
# ( $e:expr, $t:path ) => {
# $e.downcast_mut::<ChainError<$t>>()
# };
# }
# }
</code></pre></pre>
<a class="header" href="#what-did-we-do-here" id="what-did-we-do-here"><h3>What did we do here?</h3></a>
<pre><code class="language-rust ignore"> if let Err(e) = do_some_io() {
Err(cherr!(e, "func2 error"))?;
}
</code></pre>
<p>The macro <code>cherr!(cause, newerror)</code> stores <code>cause</code> as the source/cause of <code>newerror</code> and returns
<code>newerror</code>, along with the filename (<code>file!()</code>) and line number (<code>line!()</code>).</p>
<p><code>Err(e)?</code> then returns the error <code>e</code> applying <code>e.into()</code>, so that we
again have a <code>Err(Box<Error>)</code> as a result.</p>
<p>The <code>Debug</code> implementation of <code>ChainError<T></code> (which is returned by <code>cherr!()</code>)
prints the <code>Debug</code> of <code>T</code> prefixed with the stored filename and line number.</p>
<p><code>ChainError<T></code> is in our case <code>ChainError<String></code>.</p>
<a class="header" href="#mapping-errors" id="mapping-errors"><h1>Mapping Errors</h1></a>
<p>Now let's get more rust idiomatic by using <code>.map_err()</code>.</p>
<pre><pre class="playpen"><code class="language-rust">use crate::chainerror::*;
use std::error::Error;
use std::result::Result;
fn do_some_io() -> Result<(), Box<Error>> {
Err("do_some_io error")?;
Ok(())
}
fn func2() -> Result<(), Box<Error>> {
do_some_io().map_err(|e| cherr!(e, "func2 error"))?;
Ok(())
}
fn func1() -> Result<(), Box<Error>> {
func2().map_err(|e| cherr!(e, "func1 error"))?;
Ok(())
}
fn main() -> Result<(), Box<Error>> {
if let Err(e) = func1() {
eprintln!("{:?}", e);
}
Ok(())
}
# #[allow(dead_code)]
# mod chainerror {
# use std::error::Error;
# use std::fmt::{Debug, Display, Formatter, Result};
# use std::result::Result as StdResult;
#
# pub struct ChainError<T> {
# #[cfg(not(feature = "no-fileline"))]
# occurrence: Option<(u32, &'static str)>,
# kind: T,
# error_cause: Option<Box<dyn Error + 'static>>,
# }
#
# pub type ChainResult<O, E> = StdResult<O, ChainError<E>>;
#
# impl<T: 'static + Display + Debug> ChainError<T> {
# #[cfg(not(feature = "no-fileline"))]
# pub fn new(
# kind: T,
# error_cause: Option<Box<dyn Error + 'static>>,
# occurrence: Option<(u32, &'static str)>,
# ) -> Self {
# Self {
# occurrence,
# kind,
# error_cause,
# }
# }
#
# #[cfg(feature = "no-fileline")]
# pub fn new(
# kind: T,
# error_cause: Option<Box<dyn Error + 'static>>,
# _occurrence: Option<(u32, &'static str)>,
# ) -> Self {
# Self { kind, error_cause }
# }
#
# pub fn root_cause(&self) -> Option<&(dyn Error + 'static)> {
# let mut cause = self as &(dyn Error + 'static);
# while let Some(c) = cause.source() {
# cause = c;
# }
# Some(cause)
# }
#
# pub fn find_cause<U: Error + 'static>(&self) -> Option<&U> {
# let mut cause = self as &(dyn Error + 'static);
# loop {
# if cause.is::<U>() {
# return cause.downcast_ref::<U>();
# }
#
# match cause.source() {
# Some(c) => cause = c,
# None => return None,
# }
# }
# }
#
# pub fn find_chain_cause<U: Error + 'static>(&self) -> Option<&ChainError<U>> {
# let mut cause = self as &(dyn Error + 'static);
# loop {
# if cause.is::<ChainError<U>>() {
# return cause.downcast_ref::<ChainError<U>>();
# }
#
# match cause.source() {
# Some(c) => cause = c,
# None => return None,
# }
# }
# }
#
# pub fn kind<'a>(&'a self) -> &'a T {
# &self.kind
# }
# }
#
# pub trait ChainErrorDown {
# fn is_chain<T: 'static + Display + Debug>(&self) -> bool;
# fn downcast_chain_ref<T: 'static + Display + Debug>(&self) -> Option<&ChainError<T>>;
# fn downcast_chain_mut<T: 'static + Display + Debug>(&mut self) -> Option<&mut ChainError<T>>;
# }
#
# use std::any::TypeId;
#
# impl<U: 'static + Display + Debug> ChainErrorDown for ChainError<U> {
# fn is_chain<T: 'static + Display + Debug>(&self) -> bool {
# TypeId::of::<T>() == TypeId::of::<U>()
# }
#
# fn downcast_chain_ref<T: 'static + Display + Debug>(&self) -> Option<&ChainError<T>> {
# if self.is_chain::<T>() {
# unsafe { Some(&*(self as *const dyn Error as *const &ChainError<T>)) }
# } else {
# None
# }
# }
#
# fn downcast_chain_mut<T: 'static + Display + Debug>(&mut self) -> Option<&mut ChainError<T>> {
# if self.is_chain::<T>() {
# unsafe { Some(&mut *(self as *mut dyn Error as *mut &mut ChainError<T>)) }
# } else {
# None
# }
# }
# }
#
# impl ChainErrorDown for dyn Error + 'static {
# fn is_chain<T: 'static + Display + Debug>(&self) -> bool {
# self.is::<ChainError<T>>()
# }
#
# fn downcast_chain_ref<T: 'static + Display + Debug>(&self) -> Option<&ChainError<T>> {
# self.downcast_ref::<ChainError<T>>()
# }
#
# fn downcast_chain_mut<T: 'static + Display + Debug>(&mut self) -> Option<&mut ChainError<T>> {
# self.downcast_mut::<ChainError<T>>()
# }
# }
#
# impl ChainErrorDown for dyn Error + 'static + Send {
# fn is_chain<T: 'static + Display + Debug>(&self) -> bool {
# self.is::<ChainError<T>>()
# }
#
# fn downcast_chain_ref<T: 'static + Display + Debug>(&self) -> Option<&ChainError<T>> {
# self.downcast_ref::<ChainError<T>>()
# }
#
# fn downcast_chain_mut<T: 'static + Display + Debug>(&mut self) -> Option<&mut ChainError<T>> {
# self.downcast_mut::<ChainError<T>>()
# }
# }
#
# impl ChainErrorDown for dyn Error + 'static + Send + Sync {
# fn is_chain<T: 'static + Display + Debug>(&self) -> bool {
# self.is::<ChainError<T>>()
# }
#
# fn downcast_chain_ref<T: 'static + Display + Debug>(&self) -> Option<&ChainError<T>> {
# self.downcast_ref::<ChainError<T>>()
# }
#
# fn downcast_chain_mut<T: 'static + Display + Debug>(&mut self) -> Option<&mut ChainError<T>> {
# self.downcast_mut::<ChainError<T>>()
# }
# }
#
# impl<T: 'static + Display + Debug> Error for ChainError<T> {
# fn source(&self) -> Option<&(dyn Error + 'static)> {
# if let Some(ref e) = self.error_cause {
# Some(e.as_ref())
# } else {
# None
# }
# }
# }
#
# impl<T: 'static + Display + Debug> Error for &ChainError<T> {
# fn source(&self) -> Option<&(dyn Error + 'static)> {
# if let Some(ref e) = self.error_cause {
# Some(e.as_ref())
# } else {
# None
# }
# }
# }
#
# impl<T: 'static + Display + Debug> Error for &mut ChainError<T> {
# fn source(&self) -> Option<&(dyn Error + 'static)> {
# if let Some(ref e) = self.error_cause {
# Some(e.as_ref())
# } else {
# None
# }
# }
# }
#
# impl<T: 'static + Display + Debug> Display for ChainError<T> {
# fn fmt(&self, f: &mut Formatter) -> Result {
# write!(f, "{}", self.kind)?;
#
# #[cfg(feature = "display-cause")]
# {
# if let Some(e) = self.source() {
# writeln!(f, "\nCaused by:")?;
# Display::fmt(&e, f)?;
# }
# }
# Ok(())
# }
# }
#
# impl<T: 'static + Display + Debug> Debug for ChainError<T> {
# fn fmt(&self, f: &mut Formatter) -> Result {
# #[cfg(not(feature = "no-fileline"))]
# {
# if let Some(o) = self.occurrence {
# write!(f, "{}:{}: ", o.1, o.0)?;
# }
# }
#
# Debug::fmt(&self.kind, f)?;
#
# #[cfg(not(feature = "no-debug-cause"))]
# {
# if let Some(e) = self.source() {
# writeln!(f, "\nCaused by:")?;
# Debug::fmt(&e, f)?;
# }
# }
# Ok(())
# }
# }
#
# #[macro_export]
# macro_rules! cherr {
# ( $k:expr ) => {
# ChainError::<_>::new($k, None, Some((line!(), file!())))
# };
# ( $e:expr, $k:expr ) => {
# ChainError::<_>::new($k, Some(Box::from($e)), Some((line!(), file!())))
# };
# }
#
# #[macro_export]
# macro_rules! mstrerr {
# ( $t:ident, $v:expr $(, $more:expr)* ) => {
# |e| cherr!(e, $t (format!($v, $( $more , )* )))
# };
# ( $t:path, $v:expr $(, $more:expr)* ) => {
# |e| cherr!(e, $t (format!($v, $( $more , )* )))
# };
# ( $v:expr $(, $more:expr)* ) => {
# |e| cherr!(e, format!($v, $( $more , )* ))
# };
# }
#
# #[macro_export]
# macro_rules! derive_str_cherr {
# ($e:ident) => {
# struct $e(String);
# impl ::std::fmt::Display for $e {
# fn fmt(&self, f: &mut ::std::fmt::Formatter) -> ::std::fmt::Result {
# write!(f, "{}", self.0)
# }
# }
# impl ::std::fmt::Debug for $e {
# fn fmt(&self, f: &mut ::std::fmt::Formatter) -> ::std::fmt::Result {
# write!(f, "{}({})", stringify!($e), self.0)
# }
# }
# impl ::std::error::Error for $e {}
# };
# }
#
# #[macro_export]
# macro_rules! try_cherr_ref {
# ( $e:expr, $t:ident ) => {
# $e.downcast_ref::<ChainError<$t>>()
# };
# ( $e:expr, $t:path ) => {
# $e.downcast_ref::<ChainError<$t>>()
# };
# }
#
# #[macro_export]
# macro_rules! try_cherr_mut {
# ( $e:expr, $t:ident ) => {
# $e.downcast_mut::<ChainError<$t>>()
# };
# ( $e:expr, $t:path ) => {
# $e.downcast_mut::<ChainError<$t>>()
# };
# }
# }
</code></pre></pre>
<p>If you compare the output to the previous example, you will see,
that:</p>
<pre><code>Error: src/main.rs:19: "func1 error"
</code></pre>
<p>changed to just:</p>
<pre><code>src/main.rs:16: "func1 error"
</code></pre>
<p>This is, because we caught the error of <code>func1()</code> in <code>main()</code> and print it out ourselves.</p>
<p>We can now control, whether to output in <code>Debug</code> or <code>Display</code> mode.
Maybe depending on <code>--debug</code> as a CLI argument.</p>
<a class="header" href="#saving-coding-chars" id="saving-coding-chars"><h1>Saving coding chars</h1></a>
<p>Because decorating an error with more information should not
let you jump through hoops, <code>chainerror</code> has a quick macro for that.</p>
<p><code>mstrerror!()</code> fits right into <code>.map_err()</code> letting you quickly add
more debug strings.</p>
<p><code>mstrerror!()</code> even understands <code>format!()</code> syntax like <code>println!()</code>.</p>
<pre><pre class="playpen"><code class="language-rust">use crate::chainerror::*;
use std::error::Error;
use std::result::Result;
fn do_some_io() -> Result<(), Box<Error>> {
Err("do_some_io error")?;
Ok(())
}
fn func2() -> Result<(), Box<Error>> {
let filename = "foo.txt";
do_some_io().map_err(mstrerr!("Error reading '{}'", filename))?;
Ok(())
}
fn func1() -> Result<(), Box<Error>> {
func2().map_err(mstrerr!("func1 error"))?;
Ok(())
}
fn main() -> Result<(), Box<Error>> {
if let Err(e) = func1() {
eprintln!("{:?}", e);
}
Ok(())
}
# #[allow(dead_code)]
# mod chainerror {
# use std::error::Error;
# use std::fmt::{Debug, Display, Formatter, Result};
# use std::result::Result as StdResult;
#
# pub struct ChainError<T> {
# #[cfg(not(feature = "no-fileline"))]
# occurrence: Option<(u32, &'static str)>,
# kind: T,
# error_cause: Option<Box<dyn Error + 'static>>,
# }
#
# pub type ChainResult<O, E> = StdResult<O, ChainError<E>>;
#
# impl<T: 'static + Display + Debug> ChainError<T> {
# #[cfg(not(feature = "no-fileline"))]
# pub fn new(
# kind: T,
# error_cause: Option<Box<dyn Error + 'static>>,
# occurrence: Option<(u32, &'static str)>,
# ) -> Self {
# Self {
# occurrence,
# kind,
# error_cause,
# }
# }
#
# #[cfg(feature = "no-fileline")]
# pub fn new(
# kind: T,
# error_cause: Option<Box<dyn Error + 'static>>,
# _occurrence: Option<(u32, &'static str)>,
# ) -> Self {
# Self { kind, error_cause }
# }
#
# pub fn root_cause(&self) -> Option<&(dyn Error + 'static)> {
# let mut cause = self as &(dyn Error + 'static);
# while let Some(c) = cause.source() {
# cause = c;
# }
# Some(cause)
# }
#
# pub fn find_cause<U: Error + 'static>(&self) -> Option<&U> {
# let mut cause = self as &(dyn Error + 'static);
# loop {
# if cause.is::<U>() {
# return cause.downcast_ref::<U>();
# }
#
# match cause.source() {
# Some(c) => cause = c,
# None => return None,
# }
# }
# }
#
# pub fn find_chain_cause<U: Error + 'static>(&self) -> Option<&ChainError<U>> {
# let mut cause = self as &(dyn Error + 'static);
# loop {
# if cause.is::<ChainError<U>>() {
# return cause.downcast_ref::<ChainError<U>>();
# }
#
# match cause.source() {
# Some(c) => cause = c,
# None => return None,
# }
# }
# }
#
# pub fn kind<'a>(&'a self) -> &'a T {
# &self.kind
# }
# }
#
# pub trait ChainErrorDown {
# fn is_chain<T: 'static + Display + Debug>(&self) -> bool;
# fn downcast_chain_ref<T: 'static + Display + Debug>(&self) -> Option<&ChainError<T>>;
# fn downcast_chain_mut<T: 'static + Display + Debug>(&mut self) -> Option<&mut ChainError<T>>;
# }
#
# use std::any::TypeId;
#
# impl<U: 'static + Display + Debug> ChainErrorDown for ChainError<U> {
# fn is_chain<T: 'static + Display + Debug>(&self) -> bool {
# TypeId::of::<T>() == TypeId::of::<U>()
# }
#
# fn downcast_chain_ref<T: 'static + Display + Debug>(&self) -> Option<&ChainError<T>> {
# if self.is_chain::<T>() {
# unsafe { Some(&*(self as *const dyn Error as *const &ChainError<T>)) }
# } else {
# None
# }
# }
#
# fn downcast_chain_mut<T: 'static + Display + Debug>(&mut self) -> Option<&mut ChainError<T>> {
# if self.is_chain::<T>() {
# unsafe { Some(&mut *(self as *mut dyn Error as *mut &mut ChainError<T>)) }
# } else {
# None
# }
# }
# }
#
# impl ChainErrorDown for dyn Error + 'static {
# fn is_chain<T: 'static + Display + Debug>(&self) -> bool {
# self.is::<ChainError<T>>()
# }
#
# fn downcast_chain_ref<T: 'static + Display + Debug>(&self) -> Option<&ChainError<T>> {
# self.downcast_ref::<ChainError<T>>()
# }
#
# fn downcast_chain_mut<T: 'static + Display + Debug>(&mut self) -> Option<&mut ChainError<T>> {
# self.downcast_mut::<ChainError<T>>()
# }
# }
#
# impl ChainErrorDown for dyn Error + 'static + Send {
# fn is_chain<T: 'static + Display + Debug>(&self) -> bool {
# self.is::<ChainError<T>>()
# }
#
# fn downcast_chain_ref<T: 'static + Display + Debug>(&self) -> Option<&ChainError<T>> {
# self.downcast_ref::<ChainError<T>>()
# }
#
# fn downcast_chain_mut<T: 'static + Display + Debug>(&mut self) -> Option<&mut ChainError<T>> {
# self.downcast_mut::<ChainError<T>>()
# }
# }
#
# impl ChainErrorDown for dyn Error + 'static + Send + Sync {
# fn is_chain<T: 'static + Display + Debug>(&self) -> bool {
# self.is::<ChainError<T>>()
# }
#
# fn downcast_chain_ref<T: 'static + Display + Debug>(&self) -> Option<&ChainError<T>> {
# self.downcast_ref::<ChainError<T>>()
# }
#
# fn downcast_chain_mut<T: 'static + Display + Debug>(&mut self) -> Option<&mut ChainError<T>> {
# self.downcast_mut::<ChainError<T>>()
# }
# }
#
# impl<T: 'static + Display + Debug> Error for ChainError<T> {
# fn source(&self) -> Option<&(dyn Error + 'static)> {
# if let Some(ref e) = self.error_cause {
# Some(e.as_ref())
# } else {
# None
# }
# }
# }
#
# impl<T: 'static + Display + Debug> Error for &ChainError<T> {
# fn source(&self) -> Option<&(dyn Error + 'static)> {
# if let Some(ref e) = self.error_cause {
# Some(e.as_ref())
# } else {
# None
# }
# }
# }
#
# impl<T: 'static + Display + Debug> Error for &mut ChainError<T> {
# fn source(&self) -> Option<&(dyn Error + 'static)> {
# if let Some(ref e) = self.error_cause {
# Some(e.as_ref())
# } else {
# None
# }
# }
# }
#
# impl<T: 'static + Display + Debug> Display for ChainError<T> {
# fn fmt(&self, f: &mut Formatter) -> Result {
# write!(f, "{}", self.kind)?;
#
# #[cfg(feature = "display-cause")]
# {
# if let Some(e) = self.source() {
# writeln!(f, "\nCaused by:")?;
# Display::fmt(&e, f)?;
# }
# }
# Ok(())
# }
# }
#
# impl<T: 'static + Display + Debug> Debug for ChainError<T> {
# fn fmt(&self, f: &mut Formatter) -> Result {
# #[cfg(not(feature = "no-fileline"))]
# {
# if let Some(o) = self.occurrence {
# write!(f, "{}:{}: ", o.1, o.0)?;
# }
# }
#
# Debug::fmt(&self.kind, f)?;
#
# #[cfg(not(feature = "no-debug-cause"))]
# {
# if let Some(e) = self.source() {
# writeln!(f, "\nCaused by:")?;
# Debug::fmt(&e, f)?;
# }
# }
# Ok(())
# }
# }
#
# #[macro_export]
# macro_rules! cherr {
# ( $k:expr ) => {
# ChainError::<_>::new($k, None, Some((line!(), file!())))
# };
# ( $e:expr, $k:expr ) => {
# ChainError::<_>::new($k, Some(Box::from($e)), Some((line!(), file!())))
# };
# }
#
# #[macro_export]
# macro_rules! mstrerr {
# ( $t:ident, $v:expr $(, $more:expr)* ) => {
# |e| cherr!(e, $t (format!($v, $( $more , )* )))
# };
# ( $t:path, $v:expr $(, $more:expr)* ) => {
# |e| cherr!(e, $t (format!($v, $( $more , )* )))
# };
# ( $v:expr $(, $more:expr)* ) => {
# |e| cherr!(e, format!($v, $( $more , )* ))
# };
# }
#
# #[macro_export]
# macro_rules! derive_str_cherr {
# ($e:ident) => {
# struct $e(String);
# impl ::std::fmt::Display for $e {
# fn fmt(&self, f: &mut ::std::fmt::Formatter) -> ::std::fmt::Result {
# write!(f, "{}", self.0)
# }
# }
# impl ::std::fmt::Debug for $e {
# fn fmt(&self, f: &mut ::std::fmt::Formatter) -> ::std::fmt::Result {
# write!(f, "{}({})", stringify!($e), self.0)
# }
# }
# impl ::std::error::Error for $e {}
# };
# }
#
# #[macro_export]
# macro_rules! try_cherr_ref {
# ( $e:expr, $t:ident ) => {
# $e.downcast_ref::<ChainError<$t>>()
# };
# ( $e:expr, $t:path ) => {
# $e.downcast_ref::<ChainError<$t>>()
# };
# }
#
# #[macro_export]
# macro_rules! try_cherr_mut {
# ( $e:expr, $t:ident ) => {
# $e.downcast_mut::<ChainError<$t>>()
# };
# ( $e:expr, $t:path ) => {
# $e.downcast_mut::<ChainError<$t>>()
# };
# }
# }
</code></pre></pre>
<a class="header" href="#the-source-of-errors" id="the-source-of-errors"><h1>The source() of Errors</h1></a>
<p>Sometimes you want to inspect the <code>source()</code> of an <code>Error</code>.
<code>chainerror</code> implements <code>std::error::Error::source()</code>, so you can get the cause of an error.</p>
<pre><pre class="playpen"><code class="language-rust">use crate::chainerror::*;
use std::error::Error;
use std::io;
use std::result::Result;
fn do_some_io() -> Result<(), Box<Error>> {
Err(io::Error::from(io::ErrorKind::NotFound))?;
Ok(())
}
fn func2() -> Result<(), Box<Error>> {
let filename = "foo.txt";
do_some_io().map_err(mstrerr!("Error reading '{}'", filename))?;
Ok(())
}
fn func1() -> Result<(), Box<Error>> {
if let Err(e) = func2() {
if let Some(s) = e.source() {
eprintln!("func2 failed because of '{}'", s);
Err(e).map_err(mstrerr!("func1 error"))?;
}
}
Ok(())
}
fn main() -> Result<(), Box<Error>> {
if let Err(e) = func1() {
eprintln!("{}", e);
}
Ok(())
}
# #[allow(dead_code)]
# mod chainerror {
# use std::error::Error;
# use std::fmt::{Debug, Display, Formatter, Result};
# use std::result::Result as StdResult;
#
# pub struct ChainError<T> {
# #[cfg(not(feature = "no-fileline"))]
# occurrence: Option<(u32, &'static str)>,
# kind: T,
# error_cause: Option<Box<dyn Error + 'static>>,
# }
#
# pub type ChainResult<O, E> = StdResult<O, ChainError<E>>;
#
# impl<T: 'static + Display + Debug> ChainError<T> {
# #[cfg(not(feature = "no-fileline"))]
# pub fn new(
# kind: T,
# error_cause: Option<Box<dyn Error + 'static>>,
# occurrence: Option<(u32, &'static str)>,
# ) -> Self {
# Self {
# occurrence,
# kind,
# error_cause,
# }
# }
#
# #[cfg(feature = "no-fileline")]
# pub fn new(
# kind: T,
# error_cause: Option<Box<dyn Error + 'static>>,
# _occurrence: Option<(u32, &'static str)>,
# ) -> Self {
# Self { kind, error_cause }
# }
#
# pub fn root_cause(&self) -> Option<&(dyn Error + 'static)> {
# let mut cause = self as &(dyn Error + 'static);
# while let Some(c) = cause.source() {
# cause = c;
# }
# Some(cause)
# }
#
# pub fn find_cause<U: Error + 'static>(&self) -> Option<&U> {
# let mut cause = self as &(dyn Error + 'static);
# loop {
# if cause.is::<U>() {
# return cause.downcast_ref::<U>();
# }
#
# match cause.source() {
# Some(c) => cause = c,
# None => return None,
# }
# }
# }
#
# pub fn find_chain_cause<U: Error + 'static>(&self) -> Option<&ChainError<U>> {
# let mut cause = self as &(dyn Error + 'static);
# loop {
# if cause.is::<ChainError<U>>() {
# return cause.downcast_ref::<ChainError<U>>();
# }
#
# match cause.source() {
# Some(c) => cause = c,
# None => return None,
# }
# }
# }
#
# pub fn kind<'a>(&'a self) -> &'a T {
# &self.kind
# }
# }
#
# pub trait ChainErrorDown {
# fn is_chain<T: 'static + Display + Debug>(&self) -> bool;
# fn downcast_chain_ref<T: 'static + Display + Debug>(&self) -> Option<&ChainError<T>>;
# fn downcast_chain_mut<T: 'static + Display + Debug>(&mut self) -> Option<&mut ChainError<T>>;
# }
#
# use std::any::TypeId;
#
# impl<U: 'static + Display + Debug> ChainErrorDown for ChainError<U> {
# fn is_chain<T: 'static + Display + Debug>(&self) -> bool {
# TypeId::of::<T>() == TypeId::of::<U>()
# }
#
# fn downcast_chain_ref<T: 'static + Display + Debug>(&self) -> Option<&ChainError<T>> {
# if self.is_chain::<T>() {
# unsafe { Some(&*(self as *const dyn Error as *const &ChainError<T>)) }
# } else {
# None
# }
# }
#
# fn downcast_chain_mut<T: 'static + Display + Debug>(&mut self) -> Option<&mut ChainError<T>> {
# if self.is_chain::<T>() {
# unsafe { Some(&mut *(self as *mut dyn Error as *mut &mut ChainError<T>)) }
# } else {
# None
# }
# }
# }
#
# impl ChainErrorDown for dyn Error + 'static {
# fn is_chain<T: 'static + Display + Debug>(&self) -> bool {
# self.is::<ChainError<T>>()
# }
#
# fn downcast_chain_ref<T: 'static + Display + Debug>(&self) -> Option<&ChainError<T>> {
# self.downcast_ref::<ChainError<T>>()
# }
#
# fn downcast_chain_mut<T: 'static + Display + Debug>(&mut self) -> Option<&mut ChainError<T>> {
# self.downcast_mut::<ChainError<T>>()
# }
# }
#
# impl ChainErrorDown for dyn Error + 'static + Send {
# fn is_chain<T: 'static + Display + Debug>(&self) -> bool {
# self.is::<ChainError<T>>()
# }
#
# fn downcast_chain_ref<T: 'static + Display + Debug>(&self) -> Option<&ChainError<T>> {
# self.downcast_ref::<ChainError<T>>()
# }
#
# fn downcast_chain_mut<T: 'static + Display + Debug>(&mut self) -> Option<&mut ChainError<T>> {
# self.downcast_mut::<ChainError<T>>()
# }
# }
#
# impl ChainErrorDown for dyn Error + 'static + Send + Sync {
# fn is_chain<T: 'static + Display + Debug>(&self) -> bool {
# self.is::<ChainError<T>>()
# }
#
# fn downcast_chain_ref<T: 'static + Display + Debug>(&self) -> Option<&ChainError<T>> {
# self.downcast_ref::<ChainError<T>>()
# }
#
# fn downcast_chain_mut<T: 'static + Display + Debug>(&mut self) -> Option<&mut ChainError<T>> {
# self.downcast_mut::<ChainError<T>>()
# }
# }
#
# impl<T: 'static + Display + Debug> Error for ChainError<T> {
# fn source(&self) -> Option<&(dyn Error + 'static)> {
# if let Some(ref e) = self.error_cause {
# Some(e.as_ref())
# } else {
# None
# }
# }
# }
#
# impl<T: 'static + Display + Debug> Error for &ChainError<T> {
# fn source(&self) -> Option<&(dyn Error + 'static)> {
# if let Some(ref e) = self.error_cause {
# Some(e.as_ref())
# } else {
# None
# }
# }
# }
#
# impl<T: 'static + Display + Debug> Error for &mut ChainError<T> {
# fn source(&self) -> Option<&(dyn Error + 'static)> {
# if let Some(ref e) = self.error_cause {
# Some(e.as_ref())
# } else {
# None
# }
# }
# }
#
# impl<T: 'static + Display + Debug> Display for ChainError<T> {
# fn fmt(&self, f: &mut Formatter) -> Result {
# write!(f, "{}", self.kind)?;
#
# #[cfg(feature = "display-cause")]
# {
# if let Some(e) = self.source() {
# writeln!(f, "\nCaused by:")?;
# Display::fmt(&e, f)?;
# }
# }
# Ok(())
# }
# }
#
# impl<T: 'static + Display + Debug> Debug for ChainError<T> {
# fn fmt(&self, f: &mut Formatter) -> Result {
# #[cfg(not(feature = "no-fileline"))]
# {
# if let Some(o) = self.occurrence {
# write!(f, "{}:{}: ", o.1, o.0)?;
# }
# }
#
# Debug::fmt(&self.kind, f)?;
#
# #[cfg(not(feature = "no-debug-cause"))]
# {
# if let Some(e) = self.source() {
# writeln!(f, "\nCaused by:")?;
# Debug::fmt(&e, f)?;
# }
# }
# Ok(())
# }
# }
#
# #[macro_export]
# macro_rules! cherr {
# ( $k:expr ) => {
# ChainError::<_>::new($k, None, Some((line!(), file!())))
# };
# ( $e:expr, $k:expr ) => {
# ChainError::<_>::new($k, Some(Box::from($e)), Some((line!(), file!())))
# };
# }
#
# #[macro_export]
# macro_rules! mstrerr {
# ( $t:ident, $v:expr $(, $more:expr)* ) => {
# |e| cherr!(e, $t (format!($v, $( $more , )* )))
# };
# ( $t:path, $v:expr $(, $more:expr)* ) => {
# |e| cherr!(e, $t (format!($v, $( $more , )* )))
# };
# ( $v:expr $(, $more:expr)* ) => {
# |e| cherr!(e, format!($v, $( $more , )* ))
# };
# }
#
# #[macro_export]
# macro_rules! derive_str_cherr {
# ($e:ident) => {
# struct $e(String);
# impl ::std::fmt::Display for $e {
# fn fmt(&self, f: &mut ::std::fmt::Formatter) -> ::std::fmt::Result {
# write!(f, "{}", self.0)
# }
# }
# impl ::std::fmt::Debug for $e {
# fn fmt(&self, f: &mut ::std::fmt::Formatter) -> ::std::fmt::Result {
# write!(f, "{}({})", stringify!($e), self.0)
# }
# }
# impl ::std::error::Error for $e {}
# };
# }
#
# #[macro_export]
# macro_rules! try_cherr_ref {
# ( $e:expr, $t:ident ) => {
# $e.downcast_ref::<ChainError<$t>>()
# };
# ( $e:expr, $t:path ) => {
# $e.downcast_ref::<ChainError<$t>>()
# };
# }
#
# #[macro_export]
# macro_rules! try_cherr_mut {
# ( $e:expr, $t:ident ) => {
# $e.downcast_mut::<ChainError<$t>>()
# };
# ( $e:expr, $t:path ) => {
# $e.downcast_mut::<ChainError<$t>>()
# };
# }
# }
</code></pre></pre>
<p>Note, that we changed the output of the error in <code>main()</code> from <code>Debug</code> to <code>Display</code>, so we don't see
the error backtrace with filename and line number.</p>
<p>To enable the <code>Display</code> backtrace, you have to enable the feature <code>display-cause</code> for <code>chainerror</code>.</p>
<a class="header" href="#downcast-the-errors" id="downcast-the-errors"><h1>Downcast the Errors</h1></a>
<p>[TBD]</p>
<pre><pre class="playpen"><code class="language-rust">use crate::chainerror::*;
use std::error::Error;
use std::io;
use std::result::Result;
fn do_some_io() -> Result<(), Box<Error>> {
Err(io::Error::from(io::ErrorKind::NotFound))?;
Ok(())
}
fn func2() -> Result<(), Box<Error>> {
let filename = "foo.txt";
do_some_io().map_err(mstrerr!("Error reading '{}'", filename))?;
Ok(())
}
fn func1() -> Result<(), Box<Error>> {
func2().map_err(mstrerr!("func1 error"))?;
Ok(())
}
fn main() -> Result<(), Box<Error>> {
if let Err(e) = func1() {
eprintln!("Error: {}", e);
let mut s = e.as_ref();
while let Some(c) = s.source() {
if let Some(ioerror) = c.downcast_ref::<io::Error>() {
eprintln!("caused by: std::io::Error: {}", ioerror);
match ioerror.kind() {
io::ErrorKind::NotFound => eprintln!("of kind: std::io::ErrorKind::NotFound"),
_ => {}
}
} else {
eprintln!("caused by: {}", c);
}
s = c;
}
}
Ok(())
}
# #[allow(dead_code)]
# mod chainerror {
# use std::error::Error;
# use std::fmt::{Debug, Display, Formatter, Result};
# use std::result::Result as StdResult;
#
# pub struct ChainError<T> {
# #[cfg(not(feature = "no-fileline"))]
# occurrence: Option<(u32, &'static str)>,
# kind: T,
# error_cause: Option<Box<dyn Error + 'static>>,
# }
#
# pub type ChainResult<O, E> = StdResult<O, ChainError<E>>;
#
# impl<T: 'static + Display + Debug> ChainError<T> {
# #[cfg(not(feature = "no-fileline"))]
# pub fn new(
# kind: T,
# error_cause: Option<Box<dyn Error + 'static>>,
# occurrence: Option<(u32, &'static str)>,
# ) -> Self {
# Self {
# occurrence,
# kind,
# error_cause,
# }
# }
#
# #[cfg(feature = "no-fileline")]
# pub fn new(
# kind: T,
# error_cause: Option<Box<dyn Error + 'static>>,
# _occurrence: Option<(u32, &'static str)>,
# ) -> Self {
# Self { kind, error_cause }
# }
#
# pub fn root_cause(&self) -> Option<&(dyn Error + 'static)> {
# let mut cause = self as &(dyn Error + 'static);
# while let Some(c) = cause.source() {
# cause = c;
# }
# Some(cause)
# }
#
# pub fn find_cause<U: Error + 'static>(&self) -> Option<&U> {
# let mut cause = self as &(dyn Error + 'static);
# loop {
# if cause.is::<U>() {
# return cause.downcast_ref::<U>();
# }
#
# match cause.source() {
# Some(c) => cause = c,
# None => return None,
# }
# }
# }
#
# pub fn find_chain_cause<U: Error + 'static>(&self) -> Option<&ChainError<U>> {
# let mut cause = self as &(dyn Error + 'static);
# loop {
# if cause.is::<ChainError<U>>() {
# return cause.downcast_ref::<ChainError<U>>();
# }
#
# match cause.source() {
# Some(c) => cause = c,
# None => return None,
# }
# }
# }
#
# pub fn kind<'a>(&'a self) -> &'a T {
# &self.kind
# }
# }
#
# pub trait ChainErrorDown {
# fn is_chain<T: 'static + Display + Debug>(&self) -> bool;
# fn downcast_chain_ref<T: 'static + Display + Debug>(&self) -> Option<&ChainError<T>>;
# fn downcast_chain_mut<T: 'static + Display + Debug>(&mut self) -> Option<&mut ChainError<T>>;
# }
#
# use std::any::TypeId;
#
# impl<U: 'static + Display + Debug> ChainErrorDown for ChainError<U> {
# fn is_chain<T: 'static + Display + Debug>(&self) -> bool {
# TypeId::of::<T>() == TypeId::of::<U>()
# }
#
# fn downcast_chain_ref<T: 'static + Display + Debug>(&self) -> Option<&ChainError<T>> {
# if self.is_chain::<T>() {
# unsafe { Some(&*(self as *const dyn Error as *const &ChainError<T>)) }
# } else {
# None
# }
# }
#
# fn downcast_chain_mut<T: 'static + Display + Debug>(&mut self) -> Option<&mut ChainError<T>> {
# if self.is_chain::<T>() {
# unsafe { Some(&mut *(self as *mut dyn Error as *mut &mut ChainError<T>)) }
# } else {
# None
# }
# }
# }
#
# impl ChainErrorDown for dyn Error + 'static {
# fn is_chain<T: 'static + Display + Debug>(&self) -> bool {
# self.is::<ChainError<T>>()
# }
#
# fn downcast_chain_ref<T: 'static + Display + Debug>(&self) -> Option<&ChainError<T>> {
# self.downcast_ref::<ChainError<T>>()
# }
#
# fn downcast_chain_mut<T: 'static + Display + Debug>(&mut self) -> Option<&mut ChainError<T>> {
# self.downcast_mut::<ChainError<T>>()
# }
# }
#
# impl ChainErrorDown for dyn Error + 'static + Send {
# fn is_chain<T: 'static + Display + Debug>(&self) -> bool {
# self.is::<ChainError<T>>()
# }
#
# fn downcast_chain_ref<T: 'static + Display + Debug>(&self) -> Option<&ChainError<T>> {
# self.downcast_ref::<ChainError<T>>()
# }
#
# fn downcast_chain_mut<T: 'static + Display + Debug>(&mut self) -> Option<&mut ChainError<T>> {
# self.downcast_mut::<ChainError<T>>()
# }
# }
#
# impl ChainErrorDown for dyn Error + 'static + Send + Sync {
# fn is_chain<T: 'static + Display + Debug>(&self) -> bool {
# self.is::<ChainError<T>>()
# }
#
# fn downcast_chain_ref<T: 'static + Display + Debug>(&self) -> Option<&ChainError<T>> {
# self.downcast_ref::<ChainError<T>>()
# }
#
# fn downcast_chain_mut<T: 'static + Display + Debug>(&mut self) -> Option<&mut ChainError<T>> {
# self.downcast_mut::<ChainError<T>>()
# }
# }
#
# impl<T: 'static + Display + Debug> Error for ChainError<T> {
# fn source(&self) -> Option<&(dyn Error + 'static)> {
# if let Some(ref e) = self.error_cause {
# Some(e.as_ref())
# } else {
# None
# }
# }
# }
#
# impl<T: 'static + Display + Debug> Error for &ChainError<T> {
# fn source(&self) -> Option<&(dyn Error + 'static)> {
# if let Some(ref e) = self.error_cause {
# Some(e.as_ref())
# } else {
# None
# }
# }
# }
#
# impl<T: 'static + Display + Debug> Error for &mut ChainError<T> {
# fn source(&self) -> Option<&(dyn Error + 'static)> {
# if let Some(ref e) = self.error_cause {
# Some(e.as_ref())
# } else {
# None
# }
# }
# }
#
# impl<T: 'static + Display + Debug> Display for ChainError<T> {
# fn fmt(&self, f: &mut Formatter) -> Result {
# write!(f, "{}", self.kind)?;
#
# #[cfg(feature = "display-cause")]
# {
# if let Some(e) = self.source() {
# writeln!(f, "\nCaused by:")?;
# Display::fmt(&e, f)?;
# }
# }
# Ok(())
# }
# }
#
# impl<T: 'static + Display + Debug> Debug for ChainError<T> {
# fn fmt(&self, f: &mut Formatter) -> Result {
# #[cfg(not(feature = "no-fileline"))]
# {
# if let Some(o) = self.occurrence {
# write!(f, "{}:{}: ", o.1, o.0)?;
# }
# }
#
# Debug::fmt(&self.kind, f)?;
#
# #[cfg(not(feature = "no-debug-cause"))]
# {
# if let Some(e) = self.source() {
# writeln!(f, "\nCaused by:")?;
# Debug::fmt(&e, f)?;
# }
# }
# Ok(())
# }
# }
#
# #[macro_export]
# macro_rules! cherr {
# ( $k:expr ) => {
# ChainError::<_>::new($k, None, Some((line!(), file!())))
# };
# ( $e:expr, $k:expr ) => {
# ChainError::<_>::new($k, Some(Box::from($e)), Some((line!(), file!())))
# };
# }
#
# #[macro_export]
# macro_rules! mstrerr {
# ( $t:ident, $v:expr $(, $more:expr)* ) => {
# |e| cherr!(e, $t (format!($v, $( $more , )* )))
# };
# ( $t:path, $v:expr $(, $more:expr)* ) => {
# |e| cherr!(e, $t (format!($v, $( $more , )* )))
# };
# ( $v:expr $(, $more:expr)* ) => {
# |e| cherr!(e, format!($v, $( $more , )* ))
# };
# }
#
# #[macro_export]
# macro_rules! derive_str_cherr {
# ($e:ident) => {
# struct $e(String);
# impl ::std::fmt::Display for $e {
# fn fmt(&self, f: &mut ::std::fmt::Formatter) -> ::std::fmt::Result {
# write!(f, "{}", self.0)
# }
# }
# impl ::std::fmt::Debug for $e {
# fn fmt(&self, f: &mut ::std::fmt::Formatter) -> ::std::fmt::Result {
# write!(f, "{}({})", stringify!($e), self.0)
# }
# }
# impl ::std::error::Error for $e {}
# };
# }
#
# #[macro_export]
# macro_rules! try_cherr_ref {
# ( $e:expr, $t:ident ) => {
# $e.downcast_ref::<ChainError<$t>>()
# };
# ( $e:expr, $t:path ) => {
# $e.downcast_ref::<ChainError<$t>>()
# };
# }
#
# #[macro_export]
# macro_rules! try_cherr_mut {
# ( $e:expr, $t:ident ) => {
# $e.downcast_mut::<ChainError<$t>>()
# };
# ( $e:expr, $t:path ) => {
# $e.downcast_mut::<ChainError<$t>>()
# };
# }
# }
</code></pre></pre>
<a class="header" href="#the-root-cause-of-all-errors" id="the-root-cause-of-all-errors"><h1>The root cause of all Errors</h1></a>
<p>[TBD]</p>
<pre><pre class="playpen"><code class="language-rust">use crate::chainerror::*;
use std::error::Error;
use std::io;
use std::result::Result;
fn do_some_io() -> Result<(), Box<Error>> {
Err(io::Error::from(io::ErrorKind::NotFound))?;
Ok(())
}
fn func2() -> Result<(), Box<Error>> {
let filename = "foo.txt";
do_some_io().map_err(mstrerr!("Error reading '{}'", filename))?;
Ok(())
}
fn func1() -> Result<(), Box<Error>> {
func2().map_err(mstrerr!("func1 error"))?;
Ok(())
}
fn main() -> Result<(), Box<Error>> {
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);
}
}
}
Ok(())
}
# #[allow(dead_code)]
# mod chainerror {
# use std::error::Error;
# use std::fmt::{Debug, Display, Formatter, Result};
# use std::result::Result as StdResult;
#
# pub struct ChainError<T> {
# #[cfg(not(feature = "no-fileline"))]
# occurrence: Option<(u32, &'static str)>,
# kind: T,
# error_cause: Option<Box<dyn Error + 'static>>,
# }
#
# pub type ChainResult<O, E> = StdResult<O, ChainError<E>>;
#
# impl<T: 'static + Display + Debug> ChainError<T> {
# #[cfg(not(feature = "no-fileline"))]
# pub fn new(
# kind: T,
# error_cause: Option<Box<dyn Error + 'static>>,
# occurrence: Option<(u32, &'static str)>,
# ) -> Self {
# Self {
# occurrence,
# kind,
# error_cause,
# }
# }
#
# #[cfg(feature = "no-fileline")]
# pub fn new(
# kind: T,
# error_cause: Option<Box<dyn Error + 'static>>,
# _occurrence: Option<(u32, &'static str)>,
# ) -> Self {
# Self { kind, error_cause }
# }
#
# pub fn root_cause(&self) -> Option<&(dyn Error + 'static)> {
# let mut cause = self as &(dyn Error + 'static);
# while let Some(c) = cause.source() {
# cause = c;
# }
# Some(cause)
# }
#
# pub fn find_cause<U: Error + 'static>(&self) -> Option<&U> {
# let mut cause = self as &(dyn Error + 'static);
# loop {
# if cause.is::<U>() {
# return cause.downcast_ref::<U>();
# }
#
# match cause.source() {
# Some(c) => cause = c,
# None => return None,
# }
# }
# }
#
# pub fn find_chain_cause<U: Error + 'static>(&self) -> Option<&ChainError<U>> {
# let mut cause = self as &(dyn Error + 'static);
# loop {
# if cause.is::<ChainError<U>>() {
# return cause.downcast_ref::<ChainError<U>>();
# }
#
# match cause.source() {
# Some(c) => cause = c,
# None => return None,
# }
# }
# }
#
# pub fn kind<'a>(&'a self) -> &'a T {
# &self.kind
# }
# }
#
# pub trait ChainErrorDown {
# fn is_chain<T: 'static + Display + Debug>(&self) -> bool;
# fn downcast_chain_ref<T: 'static + Display + Debug>(&self) -> Option<&ChainError<T>>;
# fn downcast_chain_mut<T: 'static + Display + Debug>(&mut self) -> Option<&mut ChainError<T>>;
# }
#
# use std::any::TypeId;
#
# impl<U: 'static + Display + Debug> ChainErrorDown for ChainError<U> {
# fn is_chain<T: 'static + Display + Debug>(&self) -> bool {
# TypeId::of::<T>() == TypeId::of::<U>()
# }
#
# fn downcast_chain_ref<T: 'static + Display + Debug>(&self) -> Option<&ChainError<T>> {
# if self.is_chain::<T>() {
# unsafe { Some(&*(self as *const dyn Error as *const &ChainError<T>)) }
# } else {
# None
# }
# }
#
# fn downcast_chain_mut<T: 'static + Display + Debug>(&mut self) -> Option<&mut ChainError<T>> {
# if self.is_chain::<T>() {
# unsafe { Some(&mut *(self as *mut dyn Error as *mut &mut ChainError<T>)) }
# } else {
# None
# }
# }
# }
#
# impl ChainErrorDown for dyn Error + 'static {
# fn is_chain<T: 'static + Display + Debug>(&self) -> bool {
# self.is::<ChainError<T>>()
# }
#
# fn downcast_chain_ref<T: 'static + Display + Debug>(&self) -> Option<&ChainError<T>> {
# self.downcast_ref::<ChainError<T>>()
# }
#
# fn downcast_chain_mut<T: 'static + Display + Debug>(&mut self) -> Option<&mut ChainError<T>> {
# self.downcast_mut::<ChainError<T>>()
# }
# }
#
# impl ChainErrorDown for dyn Error + 'static + Send {
# fn is_chain<T: 'static + Display + Debug>(&self) -> bool {
# self.is::<ChainError<T>>()
# }
#
# fn downcast_chain_ref<T: 'static + Display + Debug>(&self) -> Option<&ChainError<T>> {
# self.downcast_ref::<ChainError<T>>()
# }
#
# fn downcast_chain_mut<T: 'static + Display + Debug>(&mut self) -> Option<&mut ChainError<T>> {
# self.downcast_mut::<ChainError<T>>()
# }
# }
#
# impl ChainErrorDown for dyn Error + 'static + Send + Sync {
# fn is_chain<T: 'static + Display + Debug>(&self) -> bool {
# self.is::<ChainError<T>>()
# }
#
# fn downcast_chain_ref<T: 'static + Display + Debug>(&self) -> Option<&ChainError<T>> {
# self.downcast_ref::<ChainError<T>>()
# }
#
# fn downcast_chain_mut<T: 'static + Display + Debug>(&mut self) -> Option<&mut ChainError<T>> {
# self.downcast_mut::<ChainError<T>>()
# }
# }
#
# impl<T: 'static + Display + Debug> Error for ChainError<T> {
# fn source(&self) -> Option<&(dyn Error + 'static)> {
# if let Some(ref e) = self.error_cause {
# Some(e.as_ref())
# } else {
# None
# }
# }
# }
#
# impl<T: 'static + Display + Debug> Error for &ChainError<T> {
# fn source(&self) -> Option<&(dyn Error + 'static)> {
# if let Some(ref e) = self.error_cause {
# Some(e.as_ref())
# } else {
# None
# }
# }
# }
#
# impl<T: 'static + Display + Debug> Error for &mut ChainError<T> {
# fn source(&self) -> Option<&(dyn Error + 'static)> {
# if let Some(ref e) = self.error_cause {
# Some(e.as_ref())
# } else {
# None
# }
# }
# }
#
# impl<T: 'static + Display + Debug> Display for ChainError<T> {
# fn fmt(&self, f: &mut Formatter) -> Result {
# write!(f, "{}", self.kind)?;
#
# #[cfg(feature = "display-cause")]
# {
# if let Some(e) = self.source() {
# writeln!(f, "\nCaused by:")?;
# Display::fmt(&e, f)?;
# }
# }
# Ok(())
# }
# }
#
# impl<T: 'static + Display + Debug> Debug for ChainError<T> {
# fn fmt(&self, f: &mut Formatter) -> Result {
# #[cfg(not(feature = "no-fileline"))]
# {
# if let Some(o) = self.occurrence {
# write!(f, "{}:{}: ", o.1, o.0)?;
# }
# }
#
# Debug::fmt(&self.kind, f)?;
#
# #[cfg(not(feature = "no-debug-cause"))]
# {
# if let Some(e) = self.source() {
# writeln!(f, "\nCaused by:")?;
# Debug::fmt(&e, f)?;
# }
# }
# Ok(())
# }
# }
#
# #[macro_export]
# macro_rules! cherr {
# ( $k:expr ) => {
# ChainError::<_>::new($k, None, Some((line!(), file!())))
# };
# ( $e:expr, $k:expr ) => {
# ChainError::<_>::new($k, Some(Box::from($e)), Some((line!(), file!())))
# };
# }
#
# #[macro_export]
# macro_rules! mstrerr {
# ( $t:ident, $v:expr $(, $more:expr)* ) => {
# |e| cherr!(e, $t (format!($v, $( $more , )* )))
# };
# ( $t:path, $v:expr $(, $more:expr)* ) => {
# |e| cherr!(e, $t (format!($v, $( $more , )* )))
# };
# ( $v:expr $(, $more:expr)* ) => {
# |e| cherr!(e, format!($v, $( $more , )* ))
# };
# }
#
# #[macro_export]
# macro_rules! derive_str_cherr {
# ($e:ident) => {
# struct $e(String);
# impl ::std::fmt::Display for $e {
# fn fmt(&self, f: &mut ::std::fmt::Formatter) -> ::std::fmt::Result {
# write!(f, "{}", self.0)
# }
# }
# impl ::std::fmt::Debug for $e {
# fn fmt(&self, f: &mut ::std::fmt::Formatter) -> ::std::fmt::Result {
# write!(f, "{}({})", stringify!($e), self.0)
# }
# }
# impl ::std::error::Error for $e {}
# };
# }
#
# #[macro_export]
# macro_rules! try_cherr_ref {
# ( $e:expr, $t:ident ) => {
# $e.downcast_ref::<ChainError<$t>>()
# };
# ( $e:expr, $t:path ) => {
# $e.downcast_ref::<ChainError<$t>>()
# };
# }
#
# #[macro_export]
# macro_rules! try_cherr_mut {
# ( $e:expr, $t:ident ) => {
# $e.downcast_mut::<ChainError<$t>>()
# };
# ( $e:expr, $t:path ) => {
# $e.downcast_mut::<ChainError<$t>>()
# };
# }
# }
</code></pre></pre>
<a class="header" href="#finding-an-error-cause" id="finding-an-error-cause"><h1>Finding an Error cause</h1></a>
<p>[TBD]</p>
<pre><pre class="playpen"><code class="language-rust">use crate::chainerror::*;
use std::error::Error;
use std::io;
use std::result::Result;
fn do_some_io() -> Result<(), Box<Error>> {
Err(io::Error::from(io::ErrorKind::NotFound))?;
Ok(())
}
derive_str_cherr!(Func2Error);
fn func2() -> Result<(), Box<Error>> {
let filename = "foo.txt";
do_some_io().map_err(mstrerr!(Func2Error, "Error reading '{}'", filename))?;
Ok(())
}
derive_str_cherr!(Func1Error);
fn func1() -> Result<(), Box<Error>> {
func2().map_err(mstrerr!(Func1Error, "func1 error"))?;
Ok(())
}
fn main() -> Result<(), Box<Error>> {
if let Err(e) = func1() {
if let Some(f1err) = e.downcast_chain_ref::<Func1Error>() {
eprintln!("Func1Error: {}", f1err);
if let Some(f2err) = f1err.find_cause::<ChainError<Func2Error>>() {
eprintln!("Func2Error: {}", f2err);
}
if let Some(f2err) = f1err.find_chain_cause::<Func2Error>() {
eprintln!("Debug Func2Error:\n{:?}", f2err);
}
}
}
Ok(())
}
# #[allow(dead_code)]
# mod chainerror {
# use std::error::Error;
# use std::fmt::{Debug, Display, Formatter, Result};
# use std::result::Result as StdResult;
#
# pub struct ChainError<T> {
# #[cfg(not(feature = "no-fileline"))]
# occurrence: Option<(u32, &'static str)>,
# kind: T,
# error_cause: Option<Box<dyn Error + 'static>>,
# }
#
# pub type ChainResult<O, E> = StdResult<O, ChainError<E>>;
#
# impl<T: 'static + Display + Debug> ChainError<T> {
# #[cfg(not(feature = "no-fileline"))]
# pub fn new(
# kind: T,
# error_cause: Option<Box<dyn Error + 'static>>,
# occurrence: Option<(u32, &'static str)>,
# ) -> Self {
# Self {
# occurrence,
# kind,
# error_cause,
# }
# }
#
# #[cfg(feature = "no-fileline")]
# pub fn new(
# kind: T,
# error_cause: Option<Box<dyn Error + 'static>>,
# _occurrence: Option<(u32, &'static str)>,
# ) -> Self {
# Self { kind, error_cause }
# }
#
# pub fn root_cause(&self) -> Option<&(dyn Error + 'static)> {
# let mut cause = self as &(dyn Error + 'static);
# while let Some(c) = cause.source() {
# cause = c;
# }
# Some(cause)
# }
#
# pub fn find_cause<U: Error + 'static>(&self) -> Option<&U> {
# let mut cause = self as &(dyn Error + 'static);
# loop {
# if cause.is::<U>() {
# return cause.downcast_ref::<U>();
# }
#
# match cause.source() {
# Some(c) => cause = c,
# None => return None,
# }
# }
# }
#
# pub fn find_chain_cause<U: Error + 'static>(&self) -> Option<&ChainError<U>> {
# let mut cause = self as &(dyn Error + 'static);
# loop {
# if cause.is::<ChainError<U>>() {
# return cause.downcast_ref::<ChainError<U>>();
# }
#
# match cause.source() {
# Some(c) => cause = c,
# None => return None,
# }
# }
# }
#
# pub fn kind<'a>(&'a self) -> &'a T {
# &self.kind
# }
# }
#
# pub trait ChainErrorDown {
# fn is_chain<T: 'static + Display + Debug>(&self) -> bool;
# fn downcast_chain_ref<T: 'static + Display + Debug>(&self) -> Option<&ChainError<T>>;
# fn downcast_chain_mut<T: 'static + Display + Debug>(&mut self) -> Option<&mut ChainError<T>>;
# }
#
# use std::any::TypeId;
#
# impl<U: 'static + Display + Debug> ChainErrorDown for ChainError<U> {
# fn is_chain<T: 'static + Display + Debug>(&self) -> bool {
# TypeId::of::<T>() == TypeId::of::<U>()
# }
#
# fn downcast_chain_ref<T: 'static + Display + Debug>(&self) -> Option<&ChainError<T>> {
# if self.is_chain::<T>() {
# unsafe { Some(&*(self as *const dyn Error as *const &ChainError<T>)) }
# } else {
# None
# }
# }
#
# fn downcast_chain_mut<T: 'static + Display + Debug>(&mut self) -> Option<&mut ChainError<T>> {
# if self.is_chain::<T>() {
# unsafe { Some(&mut *(self as *mut dyn Error as *mut &mut ChainError<T>)) }
# } else {
# None
# }
# }
# }
#
# impl ChainErrorDown for dyn Error + 'static {
# fn is_chain<T: 'static + Display + Debug>(&self) -> bool {
# self.is::<ChainError<T>>()
# }
#
# fn downcast_chain_ref<T: 'static + Display + Debug>(&self) -> Option<&ChainError<T>> {
# self.downcast_ref::<ChainError<T>>()
# }
#
# fn downcast_chain_mut<T: 'static + Display + Debug>(&mut self) -> Option<&mut ChainError<T>> {
# self.downcast_mut::<ChainError<T>>()
# }
# }
#
# impl ChainErrorDown for dyn Error + 'static + Send {
# fn is_chain<T: 'static + Display + Debug>(&self) -> bool {
# self.is::<ChainError<T>>()
# }
#
# fn downcast_chain_ref<T: 'static + Display + Debug>(&self) -> Option<&ChainError<T>> {
# self.downcast_ref::<ChainError<T>>()
# }
#
# fn downcast_chain_mut<T: 'static + Display + Debug>(&mut self) -> Option<&mut ChainError<T>> {
# self.downcast_mut::<ChainError<T>>()
# }
# }
#
# impl ChainErrorDown for dyn Error + 'static + Send + Sync {
# fn is_chain<T: 'static + Display + Debug>(&self) -> bool {
# self.is::<ChainError<T>>()
# }
#
# fn downcast_chain_ref<T: 'static + Display + Debug>(&self) -> Option<&ChainError<T>> {
# self.downcast_ref::<ChainError<T>>()
# }
#
# fn downcast_chain_mut<T: 'static + Display + Debug>(&mut self) -> Option<&mut ChainError<T>> {
# self.downcast_mut::<ChainError<T>>()
# }
# }
#
# impl<T: 'static + Display + Debug> Error for ChainError<T> {
# fn source(&self) -> Option<&(dyn Error + 'static)> {
# if let Some(ref e) = self.error_cause {
# Some(e.as_ref())
# } else {
# None
# }
# }
# }
#
# impl<T: 'static + Display + Debug> Error for &ChainError<T> {
# fn source(&self) -> Option<&(dyn Error + 'static)> {
# if let Some(ref e) = self.error_cause {
# Some(e.as_ref())
# } else {
# None
# }
# }
# }
#
# impl<T: 'static + Display + Debug> Error for &mut ChainError<T> {
# fn source(&self) -> Option<&(dyn Error + 'static)> {
# if let Some(ref e) = self.error_cause {
# Some(e.as_ref())
# } else {
# None
# }
# }
# }
#
# impl<T: 'static + Display + Debug> Display for ChainError<T> {
# fn fmt(&self, f: &mut Formatter) -> Result {
# write!(f, "{}", self.kind)?;
#
# #[cfg(feature = "display-cause")]
# {
# if let Some(e) = self.source() {
# writeln!(f, "\nCaused by:")?;
# Display::fmt(&e, f)?;
# }
# }
# Ok(())
# }
# }
#
# impl<T: 'static + Display + Debug> Debug for ChainError<T> {
# fn fmt(&self, f: &mut Formatter) -> Result {
# #[cfg(not(feature = "no-fileline"))]
# {
# if let Some(o) = self.occurrence {
# write!(f, "{}:{}: ", o.1, o.0)?;
# }
# }
#
# Debug::fmt(&self.kind, f)?;
#
# #[cfg(not(feature = "no-debug-cause"))]
# {
# if let Some(e) = self.source() {
# writeln!(f, "\nCaused by:")?;
# Debug::fmt(&e, f)?;
# }
# }
# Ok(())
# }
# }
#
# #[macro_export]
# macro_rules! cherr {
# ( $k:expr ) => {
# ChainError::<_>::new($k, None, Some((line!(), file!())))
# };
# ( $e:expr, $k:expr ) => {
# ChainError::<_>::new($k, Some(Box::from($e)), Some((line!(), file!())))
# };
# }
#
# #[macro_export]
# macro_rules! mstrerr {
# ( $t:ident, $v:expr $(, $more:expr)* ) => {
# |e| cherr!(e, $t (format!($v, $( $more , )* )))
# };
# ( $t:path, $v:expr $(, $more:expr)* ) => {
# |e| cherr!(e, $t (format!($v, $( $more , )* )))
# };
# ( $v:expr $(, $more:expr)* ) => {
# |e| cherr!(e, format!($v, $( $more , )* ))
# };
# }
#
# #[macro_export]
# macro_rules! derive_str_cherr {
# ($e:ident) => {
# struct $e(String);
# impl ::std::fmt::Display for $e {
# fn fmt(&self, f: &mut ::std::fmt::Formatter) -> ::std::fmt::Result {
# write!(f, "{}", self.0)
# }
# }
# impl ::std::fmt::Debug for $e {
# fn fmt(&self, f: &mut ::std::fmt::Formatter) -> ::std::fmt::Result {
# write!(f, "{}({})", stringify!($e), self.0)
# }
# }
# impl ::std::error::Error for $e {}
# };
# }
#
# #[macro_export]
# macro_rules! try_cherr_ref {
# ( $e:expr, $t:ident ) => {
# $e.downcast_ref::<ChainError<$t>>()
# };
# ( $e:expr, $t:path ) => {
# $e.downcast_ref::<ChainError<$t>>()
# };
# }
#
# #[macro_export]
# macro_rules! try_cherr_mut {
# ( $e:expr, $t:ident ) => {
# $e.downcast_mut::<ChainError<$t>>()
# };
# ( $e:expr, $t:path ) => {
# $e.downcast_mut::<ChainError<$t>>()
# };
# }
# }
</code></pre></pre>
<a class="header" href="#selective-error-handling" id="selective-error-handling"><h1>Selective Error Handling</h1></a>
<p>[TBD]</p>
<pre><pre class="playpen"><code class="language-rust">use crate::chainerror::*;
use std::error::Error;
use std::io;
use std::result::Result;
fn do_some_io() -> Result<(), Box<Error>> {
Err(io::Error::from(io::ErrorKind::NotFound))?;
Ok(())
}
derive_str_cherr!(Func2Error);
fn func2() -> Result<(), Box<Error>> {
let filename = "foo.txt";
do_some_io().map_err(mstrerr!(Func2Error, "Error reading '{}'", filename))?;
Ok(())
}
derive_str_cherr!(Func1ErrorFunc2);
derive_str_cherr!(Func1ErrorIO);
fn func1() -> Result<(), Box<Error>> {
func2().map_err(mstrerr!(Func1ErrorFunc2, "func1 error calling func2"))?;
let filename = "bar.txt";
do_some_io().map_err(mstrerr!(Func1ErrorIO, "Error reading '{}'", filename))?;
Ok(())
}
fn main() -> Result<(), Box<Error>> {
if let Err(e) = func1() {
if let Some(s) = e.downcast_ref::<ChainError<Func1ErrorIO>>() {
eprintln!("Func1ErrorIO:\n{:?}", s);
}
if let Some(s) = try_cherr_ref!(e, Func1ErrorFunc2) {
eprintln!("Func1ErrorFunc2:\n{:?}", s);
}
}
Ok(())
}
# #[allow(dead_code)]
# mod chainerror {
# use std::error::Error;
# use std::fmt::{Debug, Display, Formatter, Result};
# use std::result::Result as StdResult;
#
# pub struct ChainError<T> {
# #[cfg(not(feature = "no-fileline"))]
# occurrence: Option<(u32, &'static str)>,
# kind: T,
# error_cause: Option<Box<dyn Error + 'static>>,
# }
#
# pub type ChainResult<O, E> = StdResult<O, ChainError<E>>;
#
# impl<T: 'static + Display + Debug> ChainError<T> {
# #[cfg(not(feature = "no-fileline"))]
# pub fn new(
# kind: T,
# error_cause: Option<Box<dyn Error + 'static>>,
# occurrence: Option<(u32, &'static str)>,
# ) -> Self {
# Self {
# occurrence,
# kind,
# error_cause,
# }
# }
#
# #[cfg(feature = "no-fileline")]
# pub fn new(
# kind: T,
# error_cause: Option<Box<dyn Error + 'static>>,
# _occurrence: Option<(u32, &'static str)>,
# ) -> Self {
# Self { kind, error_cause }
# }
#
# pub fn root_cause(&self) -> Option<&(dyn Error + 'static)> {
# let mut cause = self as &(dyn Error + 'static);
# while let Some(c) = cause.source() {
# cause = c;
# }
# Some(cause)
# }
#
# pub fn find_cause<U: Error + 'static>(&self) -> Option<&U> {
# let mut cause = self as &(dyn Error + 'static);
# loop {
# if cause.is::<U>() {
# return cause.downcast_ref::<U>();
# }
#
# match cause.source() {
# Some(c) => cause = c,
# None => return None,
# }
# }
# }
#
# pub fn find_chain_cause<U: Error + 'static>(&self) -> Option<&ChainError<U>> {
# let mut cause = self as &(dyn Error + 'static);
# loop {
# if cause.is::<ChainError<U>>() {
# return cause.downcast_ref::<ChainError<U>>();
# }
#
# match cause.source() {
# Some(c) => cause = c,
# None => return None,
# }
# }
# }
#
# pub fn kind<'a>(&'a self) -> &'a T {
# &self.kind
# }
# }
#
# pub trait ChainErrorDown {
# fn is_chain<T: 'static + Display + Debug>(&self) -> bool;
# fn downcast_chain_ref<T: 'static + Display + Debug>(&self) -> Option<&ChainError<T>>;
# fn downcast_chain_mut<T: 'static + Display + Debug>(&mut self) -> Option<&mut ChainError<T>>;
# }
#
# use std::any::TypeId;
#
# impl<U: 'static + Display + Debug> ChainErrorDown for ChainError<U> {
# fn is_chain<T: 'static + Display + Debug>(&self) -> bool {
# TypeId::of::<T>() == TypeId::of::<U>()
# }
#
# fn downcast_chain_ref<T: 'static + Display + Debug>(&self) -> Option<&ChainError<T>> {
# if self.is_chain::<T>() {
# unsafe { Some(&*(self as *const dyn Error as *const &ChainError<T>)) }
# } else {
# None
# }
# }
#
# fn downcast_chain_mut<T: 'static + Display + Debug>(&mut self) -> Option<&mut ChainError<T>> {
# if self.is_chain::<T>() {
# unsafe { Some(&mut *(self as *mut dyn Error as *mut &mut ChainError<T>)) }
# } else {
# None
# }
# }
# }
#
# impl ChainErrorDown for dyn Error + 'static {
# fn is_chain<T: 'static + Display + Debug>(&self) -> bool {
# self.is::<ChainError<T>>()
# }
#
# fn downcast_chain_ref<T: 'static + Display + Debug>(&self) -> Option<&ChainError<T>> {
# self.downcast_ref::<ChainError<T>>()
# }
#
# fn downcast_chain_mut<T: 'static + Display + Debug>(&mut self) -> Option<&mut ChainError<T>> {
# self.downcast_mut::<ChainError<T>>()
# }
# }
#
# impl ChainErrorDown for dyn Error + 'static + Send {
# fn is_chain<T: 'static + Display + Debug>(&self) -> bool {
# self.is::<ChainError<T>>()
# }
#
# fn downcast_chain_ref<T: 'static + Display + Debug>(&self) -> Option<&ChainError<T>> {
# self.downcast_ref::<ChainError<T>>()
# }
#
# fn downcast_chain_mut<T: 'static + Display + Debug>(&mut self) -> Option<&mut ChainError<T>> {
# self.downcast_mut::<ChainError<T>>()
# }
# }
#
# impl ChainErrorDown for dyn Error + 'static + Send + Sync {
# fn is_chain<T: 'static + Display + Debug>(&self) -> bool {
# self.is::<ChainError<T>>()
# }
#
# fn downcast_chain_ref<T: 'static + Display + Debug>(&self) -> Option<&ChainError<T>> {
# self.downcast_ref::<ChainError<T>>()
# }
#
# fn downcast_chain_mut<T: 'static + Display + Debug>(&mut self) -> Option<&mut ChainError<T>> {
# self.downcast_mut::<ChainError<T>>()
# }
# }
#
# impl<T: 'static + Display + Debug> Error for ChainError<T> {
# fn source(&self) -> Option<&(dyn Error + 'static)> {
# if let Some(ref e) = self.error_cause {
# Some(e.as_ref())
# } else {
# None
# }
# }
# }
#
# impl<T: 'static + Display + Debug> Error for &ChainError<T> {
# fn source(&self) -> Option<&(dyn Error + 'static)> {
# if let Some(ref e) = self.error_cause {
# Some(e.as_ref())
# } else {
# None
# }
# }
# }
#
# impl<T: 'static + Display + Debug> Error for &mut ChainError<T> {
# fn source(&self) -> Option<&(dyn Error + 'static)> {
# if let Some(ref e) = self.error_cause {
# Some(e.as_ref())
# } else {
# None
# }
# }
# }
#
# impl<T: 'static + Display + Debug> Display for ChainError<T> {
# fn fmt(&self, f: &mut Formatter) -> Result {
# write!(f, "{}", self.kind)?;
#
# #[cfg(feature = "display-cause")]
# {
# if let Some(e) = self.source() {
# writeln!(f, "\nCaused by:")?;
# Display::fmt(&e, f)?;
# }
# }
# Ok(())
# }
# }
#
# impl<T: 'static + Display + Debug> Debug for ChainError<T> {
# fn fmt(&self, f: &mut Formatter) -> Result {
# #[cfg(not(feature = "no-fileline"))]
# {
# if let Some(o) = self.occurrence {
# write!(f, "{}:{}: ", o.1, o.0)?;
# }
# }
#
# Debug::fmt(&self.kind, f)?;
#
# #[cfg(not(feature = "no-debug-cause"))]
# {
# if let Some(e) = self.source() {
# writeln!(f, "\nCaused by:")?;
# Debug::fmt(&e, f)?;
# }
# }
# Ok(())
# }
# }
#
# #[macro_export]
# macro_rules! cherr {
# ( $k:expr ) => {
# ChainError::<_>::new($k, None, Some((line!(), file!())))
# };
# ( $e:expr, $k:expr ) => {
# ChainError::<_>::new($k, Some(Box::from($e)), Some((line!(), file!())))
# };
# }
#
# #[macro_export]
# macro_rules! mstrerr {
# ( $t:ident, $v:expr $(, $more:expr)* ) => {
# |e| cherr!(e, $t (format!($v, $( $more , )* )))
# };
# ( $t:path, $v:expr $(, $more:expr)* ) => {
# |e| cherr!(e, $t (format!($v, $( $more , )* )))
# };
# ( $v:expr $(, $more:expr)* ) => {
# |e| cherr!(e, format!($v, $( $more , )* ))
# };
# }
#
# #[macro_export]
# macro_rules! derive_str_cherr {
# ($e:ident) => {
# struct $e(String);
# impl ::std::fmt::Display for $e {
# fn fmt(&self, f: &mut ::std::fmt::Formatter) -> ::std::fmt::Result {
# write!(f, "{}", self.0)
# }
# }
# impl ::std::fmt::Debug for $e {
# fn fmt(&self, f: &mut ::std::fmt::Formatter) -> ::std::fmt::Result {
# write!(f, "{}({})", stringify!($e), self.0)
# }
# }
# impl ::std::error::Error for $e {}
# };
# }
#
# #[macro_export]
# macro_rules! try_cherr_ref {
# ( $e:expr, $t:ident ) => {
# $e.downcast_ref::<ChainError<$t>>()
# };
# ( $e:expr, $t:path ) => {
# $e.downcast_ref::<ChainError<$t>>()
# };
# }
#
# #[macro_export]
# macro_rules! try_cherr_mut {
# ( $e:expr, $t:ident ) => {
# $e.downcast_mut::<ChainError<$t>>()
# };
# ( $e:expr, $t:path ) => {
# $e.downcast_mut::<ChainError<$t>>()
# };
# }
# }
</code></pre></pre>
<a class="header" href="#errorkind-to-the-rescue" id="errorkind-to-the-rescue"><h1>ErrorKind to the rescue</h1></a>
<p>[TBD]</p>
<pre><pre class="playpen"><code class="language-rust">use crate::chainerror::*;
use std::error::Error;
use std::io;
use std::result::Result;
fn do_some_io() -> Result<(), Box<Error>> {
Err(io::Error::from(io::ErrorKind::NotFound))?;
Ok(())
}
derive_str_cherr!(Func2Error);
fn func2() -> Result<(), Box<Error>> {
let filename = "foo.txt";
do_some_io().map_err(mstrerr!(Func2Error, "Error reading '{}'", filename))?;
Ok(())
}
#[derive(Debug)]
enum Func1Error {
Func2,
IO(String),
}
impl ::std::fmt::Display for Func1Error {
fn fmt(&self, f: &mut ::std::fmt::Formatter) -> ::std::fmt::Result {
match self {
Func1Error::Func2 => write!(f, "func1 error calling func2"),
Func1Error::IO(filename) => write!(f, "Error reading '{}'", filename),
}
}
}
fn func1() -> ChainResult<(), Func1Error> {
func2().map_err(|e| cherr!(e, Func1Error::Func2))?;
let filename = String::from("bar.txt");
do_some_io().map_err(|e| cherr!(e, Func1Error::IO(filename)))?;
Ok(())
}
fn main() -> Result<(), Box<Error>> {
if let Err(e) = func1() {
match e.kind() {
Func1Error::Func2 => eprintln!("Main Error Report: func1 error calling func2"),
Func1Error::IO(filename) => {
eprintln!("Main Error Report: func1 error reading '{}'", filename)
}
}
if let Some(e) = e.find_chain_cause::<Func2Error>() {
eprintln!("Error reported by Func2Error: {}", e)
}
eprintln!("\nDebug Error:\n{:?}", e);
}
Ok(())
}
# #[allow(dead_code)]
# mod chainerror {
# use std::error::Error;
# use std::fmt::{Debug, Display, Formatter, Result};
# use std::result::Result as StdResult;
#
# pub struct ChainError<T> {
# #[cfg(not(feature = "no-fileline"))]
# occurrence: Option<(u32, &'static str)>,
# kind: T,
# error_cause: Option<Box<dyn Error + 'static>>,
# }
#
# pub type ChainResult<O, E> = StdResult<O, ChainError<E>>;
#
# impl<T: 'static + Display + Debug> ChainError<T> {
# #[cfg(not(feature = "no-fileline"))]
# pub fn new(
# kind: T,
# error_cause: Option<Box<dyn Error + 'static>>,
# occurrence: Option<(u32, &'static str)>,
# ) -> Self {
# Self {
# occurrence,
# kind,
# error_cause,
# }
# }
#
# #[cfg(feature = "no-fileline")]
# pub fn new(
# kind: T,
# error_cause: Option<Box<dyn Error + 'static>>,
# _occurrence: Option<(u32, &'static str)>,
# ) -> Self {
# Self { kind, error_cause }
# }
#
# pub fn root_cause(&self) -> Option<&(dyn Error + 'static)> {
# let mut cause = self as &(dyn Error + 'static);
# while let Some(c) = cause.source() {
# cause = c;
# }
# Some(cause)
# }
#
# pub fn find_cause<U: Error + 'static>(&self) -> Option<&U> {
# let mut cause = self as &(dyn Error + 'static);
# loop {
# if cause.is::<U>() {
# return cause.downcast_ref::<U>();
# }
#
# match cause.source() {
# Some(c) => cause = c,
# None => return None,
# }
# }
# }
#
# pub fn find_chain_cause<U: Error + 'static>(&self) -> Option<&ChainError<U>> {
# let mut cause = self as &(dyn Error + 'static);
# loop {
# if cause.is::<ChainError<U>>() {
# return cause.downcast_ref::<ChainError<U>>();
# }
#
# match cause.source() {
# Some(c) => cause = c,
# None => return None,
# }
# }
# }
#
# pub fn kind<'a>(&'a self) -> &'a T {
# &self.kind
# }
# }
#
# pub trait ChainErrorDown {
# fn is_chain<T: 'static + Display + Debug>(&self) -> bool;
# fn downcast_chain_ref<T: 'static + Display + Debug>(&self) -> Option<&ChainError<T>>;
# fn downcast_chain_mut<T: 'static + Display + Debug>(&mut self) -> Option<&mut ChainError<T>>;
# }
#
# use std::any::TypeId;
#
# impl<U: 'static + Display + Debug> ChainErrorDown for ChainError<U> {
# fn is_chain<T: 'static + Display + Debug>(&self) -> bool {
# TypeId::of::<T>() == TypeId::of::<U>()
# }
#
# fn downcast_chain_ref<T: 'static + Display + Debug>(&self) -> Option<&ChainError<T>> {
# if self.is_chain::<T>() {
# unsafe { Some(&*(self as *const dyn Error as *const &ChainError<T>)) }
# } else {
# None
# }
# }
#
# fn downcast_chain_mut<T: 'static + Display + Debug>(&mut self) -> Option<&mut ChainError<T>> {
# if self.is_chain::<T>() {
# unsafe { Some(&mut *(self as *mut dyn Error as *mut &mut ChainError<T>)) }
# } else {
# None
# }
# }
# }
#
# impl ChainErrorDown for dyn Error + 'static {
# fn is_chain<T: 'static + Display + Debug>(&self) -> bool {
# self.is::<ChainError<T>>()
# }
#
# fn downcast_chain_ref<T: 'static + Display + Debug>(&self) -> Option<&ChainError<T>> {
# self.downcast_ref::<ChainError<T>>()
# }
#
# fn downcast_chain_mut<T: 'static + Display + Debug>(&mut self) -> Option<&mut ChainError<T>> {
# self.downcast_mut::<ChainError<T>>()
# }
# }
#
# impl ChainErrorDown for dyn Error + 'static + Send {
# fn is_chain<T: 'static + Display + Debug>(&self) -> bool {
# self.is::<ChainError<T>>()
# }
#
# fn downcast_chain_ref<T: 'static + Display + Debug>(&self) -> Option<&ChainError<T>> {
# self.downcast_ref::<ChainError<T>>()
# }
#
# fn downcast_chain_mut<T: 'static + Display + Debug>(&mut self) -> Option<&mut ChainError<T>> {
# self.downcast_mut::<ChainError<T>>()
# }
# }
#
# impl ChainErrorDown for dyn Error + 'static + Send + Sync {
# fn is_chain<T: 'static + Display + Debug>(&self) -> bool {
# self.is::<ChainError<T>>()
# }
#
# fn downcast_chain_ref<T: 'static + Display + Debug>(&self) -> Option<&ChainError<T>> {
# self.downcast_ref::<ChainError<T>>()
# }
#
# fn downcast_chain_mut<T: 'static + Display + Debug>(&mut self) -> Option<&mut ChainError<T>> {
# self.downcast_mut::<ChainError<T>>()
# }
# }
#
# impl<T: 'static + Display + Debug> Error for ChainError<T> {
# fn source(&self) -> Option<&(dyn Error + 'static)> {
# if let Some(ref e) = self.error_cause {
# Some(e.as_ref())
# } else {
# None
# }
# }
# }
#
# impl<T: 'static + Display + Debug> Error for &ChainError<T> {
# fn source(&self) -> Option<&(dyn Error + 'static)> {
# if let Some(ref e) = self.error_cause {
# Some(e.as_ref())
# } else {
# None
# }
# }
# }
#
# impl<T: 'static + Display + Debug> Error for &mut ChainError<T> {
# fn source(&self) -> Option<&(dyn Error + 'static)> {
# if let Some(ref e) = self.error_cause {
# Some(e.as_ref())
# } else {
# None
# }
# }
# }
#
# impl<T: 'static + Display + Debug> Display for ChainError<T> {
# fn fmt(&self, f: &mut Formatter) -> Result {
# write!(f, "{}", self.kind)?;
#
# #[cfg(feature = "display-cause")]
# {
# if let Some(e) = self.source() {
# writeln!(f, "\nCaused by:")?;
# Display::fmt(&e, f)?;
# }
# }
# Ok(())
# }
# }
#
# impl<T: 'static + Display + Debug> Debug for ChainError<T> {
# fn fmt(&self, f: &mut Formatter) -> Result {
# #[cfg(not(feature = "no-fileline"))]
# {
# if let Some(o) = self.occurrence {
# write!(f, "{}:{}: ", o.1, o.0)?;
# }
# }
#
# Debug::fmt(&self.kind, f)?;
#
# #[cfg(not(feature = "no-debug-cause"))]
# {
# if let Some(e) = self.source() {
# writeln!(f, "\nCaused by:")?;
# Debug::fmt(&e, f)?;
# }
# }
# Ok(())
# }
# }
#
# #[macro_export]
# macro_rules! cherr {
# ( $k:expr ) => {
# ChainError::<_>::new($k, None, Some((line!(), file!())))
# };
# ( $e:expr, $k:expr ) => {
# ChainError::<_>::new($k, Some(Box::from($e)), Some((line!(), file!())))
# };
# }
#
# #[macro_export]
# macro_rules! mstrerr {
# ( $t:ident, $v:expr $(, $more:expr)* ) => {
# |e| cherr!(e, $t (format!($v, $( $more , )* )))
# };
# ( $t:path, $v:expr $(, $more:expr)* ) => {
# |e| cherr!(e, $t (format!($v, $( $more , )* )))
# };
# ( $v:expr $(, $more:expr)* ) => {
# |e| cherr!(e, format!($v, $( $more , )* ))
# };
# }
#
# #[macro_export]
# macro_rules! derive_str_cherr {
# ($e:ident) => {
# struct $e(String);
# impl ::std::fmt::Display for $e {
# fn fmt(&self, f: &mut ::std::fmt::Formatter) -> ::std::fmt::Result {
# write!(f, "{}", self.0)
# }
# }
# impl ::std::fmt::Debug for $e {
# fn fmt(&self, f: &mut ::std::fmt::Formatter) -> ::std::fmt::Result {
# write!(f, "{}({})", stringify!($e), self.0)
# }
# }
# impl ::std::error::Error for $e {}
# };
# }
#
# #[macro_export]
# macro_rules! try_cherr_ref {
# ( $e:expr, $t:ident ) => {
# $e.downcast_ref::<ChainError<$t>>()
# };
# ( $e:expr, $t:path ) => {
# $e.downcast_ref::<ChainError<$t>>()
# };
# }
#
# #[macro_export]
# macro_rules! try_cherr_mut {
# ( $e:expr, $t:ident ) => {
# $e.downcast_mut::<ChainError<$t>>()
# };
# ( $e:expr, $t:path ) => {
# $e.downcast_mut::<ChainError<$t>>()
# };
# }
# }
</code></pre></pre>
<a class="header" href="#debug-for-the-errorkind" id="debug-for-the-errorkind"><h1>Debug for the ErrorKind</h1></a>
<p>[TBD]</p>
<pre><pre class="playpen"><code class="language-rust">use crate::chainerror::*;
use std::error::Error;
use std::io;
use std::result::Result;
fn do_some_io() -> Result<(), Box<Error>> {
Err(io::Error::from(io::ErrorKind::NotFound))?;
Ok(())
}
derive_str_cherr!(Func2Error);
fn func2() -> Result<(), Box<Error>> {
let filename = "foo.txt";
do_some_io().map_err(mstrerr!(Func2Error, "Error reading '{}'", filename))?;
Ok(())
}
enum Func1Error {
Func2,
IO(String),
}
impl ::std::fmt::Display for Func1Error {
fn fmt(&self, f: &mut ::std::fmt::Formatter) -> ::std::fmt::Result {
match self {
Func1Error::Func2 => write!(f, "func1 error calling func2"),
Func1Error::IO(filename) => write!(f, "Error reading '{}'", filename),
}
}
}
impl ::std::fmt::Debug for Func1Error {
fn fmt(&self, f: &mut ::std::fmt::Formatter) -> ::std::fmt::Result {
write!(f, "{}", self)
}
}
fn func1() -> ChainResult<(), Func1Error> {
func2().map_err(|e| cherr!(e, Func1Error::Func2))?;
let filename = String::from("bar.txt");
do_some_io().map_err(|e| cherr!(e, Func1Error::IO(filename)))?;
Ok(())
}
fn main() -> Result<(), Box<Error>> {
if let Err(e) = func1() {
match e.kind() {
Func1Error::Func2 => eprintln!("Main Error Report: func1 error calling func2"),
Func1Error::IO(filename) => {
eprintln!("Main Error Report: func1 error reading '{}'", filename)
}
}
if let Some(e) = e.find_chain_cause::<Func2Error>() {
eprintln!("Error reported by Func2Error: {}", e)
}
eprintln!("\nDebug Error:\n{:?}", e);
}
Ok(())
}
# #[allow(dead_code)]
# mod chainerror {
# use std::error::Error;
# use std::fmt::{Debug, Display, Formatter, Result};
# use std::result::Result as StdResult;
#
# pub struct ChainError<T> {
# #[cfg(not(feature = "no-fileline"))]
# occurrence: Option<(u32, &'static str)>,
# kind: T,
# error_cause: Option<Box<dyn Error + 'static>>,
# }
#
# pub type ChainResult<O, E> = StdResult<O, ChainError<E>>;
#
# impl<T: 'static + Display + Debug> ChainError<T> {
# #[cfg(not(feature = "no-fileline"))]
# pub fn new(
# kind: T,
# error_cause: Option<Box<dyn Error + 'static>>,
# occurrence: Option<(u32, &'static str)>,
# ) -> Self {
# Self {
# occurrence,
# kind,
# error_cause,
# }
# }
#
# #[cfg(feature = "no-fileline")]
# pub fn new(
# kind: T,
# error_cause: Option<Box<dyn Error + 'static>>,
# _occurrence: Option<(u32, &'static str)>,
# ) -> Self {
# Self { kind, error_cause }
# }
#
# pub fn root_cause(&self) -> Option<&(dyn Error + 'static)> {
# let mut cause = self as &(dyn Error + 'static);
# while let Some(c) = cause.source() {
# cause = c;
# }
# Some(cause)
# }
#
# pub fn find_cause<U: Error + 'static>(&self) -> Option<&U> {
# let mut cause = self as &(dyn Error + 'static);
# loop {
# if cause.is::<U>() {
# return cause.downcast_ref::<U>();
# }
#
# match cause.source() {
# Some(c) => cause = c,
# None => return None,
# }
# }
# }
#
# pub fn find_chain_cause<U: Error + 'static>(&self) -> Option<&ChainError<U>> {
# let mut cause = self as &(dyn Error + 'static);
# loop {
# if cause.is::<ChainError<U>>() {
# return cause.downcast_ref::<ChainError<U>>();
# }
#
# match cause.source() {
# Some(c) => cause = c,
# None => return None,
# }
# }
# }
#
# pub fn kind<'a>(&'a self) -> &'a T {
# &self.kind
# }
# }
#
# pub trait ChainErrorDown {
# fn is_chain<T: 'static + Display + Debug>(&self) -> bool;
# fn downcast_chain_ref<T: 'static + Display + Debug>(&self) -> Option<&ChainError<T>>;
# fn downcast_chain_mut<T: 'static + Display + Debug>(&mut self) -> Option<&mut ChainError<T>>;
# }
#
# use std::any::TypeId;
#
# impl<U: 'static + Display + Debug> ChainErrorDown for ChainError<U> {
# fn is_chain<T: 'static + Display + Debug>(&self) -> bool {
# TypeId::of::<T>() == TypeId::of::<U>()
# }
#
# fn downcast_chain_ref<T: 'static + Display + Debug>(&self) -> Option<&ChainError<T>> {
# if self.is_chain::<T>() {
# unsafe { Some(&*(self as *const dyn Error as *const &ChainError<T>)) }
# } else {
# None
# }
# }
#
# fn downcast_chain_mut<T: 'static + Display + Debug>(&mut self) -> Option<&mut ChainError<T>> {
# if self.is_chain::<T>() {
# unsafe { Some(&mut *(self as *mut dyn Error as *mut &mut ChainError<T>)) }
# } else {
# None
# }
# }
# }
#
# impl ChainErrorDown for dyn Error + 'static {
# fn is_chain<T: 'static + Display + Debug>(&self) -> bool {
# self.is::<ChainError<T>>()
# }
#
# fn downcast_chain_ref<T: 'static + Display + Debug>(&self) -> Option<&ChainError<T>> {
# self.downcast_ref::<ChainError<T>>()
# }
#
# fn downcast_chain_mut<T: 'static + Display + Debug>(&mut self) -> Option<&mut ChainError<T>> {
# self.downcast_mut::<ChainError<T>>()
# }
# }
#
# impl ChainErrorDown for dyn Error + 'static + Send {
# fn is_chain<T: 'static + Display + Debug>(&self) -> bool {
# self.is::<ChainError<T>>()
# }
#
# fn downcast_chain_ref<T: 'static + Display + Debug>(&self) -> Option<&ChainError<T>> {
# self.downcast_ref::<ChainError<T>>()
# }
#
# fn downcast_chain_mut<T: 'static + Display + Debug>(&mut self) -> Option<&mut ChainError<T>> {
# self.downcast_mut::<ChainError<T>>()
# }
# }
#
# impl ChainErrorDown for dyn Error + 'static + Send + Sync {
# fn is_chain<T: 'static + Display + Debug>(&self) -> bool {
# self.is::<ChainError<T>>()
# }
#
# fn downcast_chain_ref<T: 'static + Display + Debug>(&self) -> Option<&ChainError<T>> {
# self.downcast_ref::<ChainError<T>>()
# }
#
# fn downcast_chain_mut<T: 'static + Display + Debug>(&mut self) -> Option<&mut ChainError<T>> {
# self.downcast_mut::<ChainError<T>>()
# }
# }
#
# impl<T: 'static + Display + Debug> Error for ChainError<T> {
# fn source(&self) -> Option<&(dyn Error + 'static)> {
# if let Some(ref e) = self.error_cause {
# Some(e.as_ref())
# } else {
# None
# }
# }
# }
#
# impl<T: 'static + Display + Debug> Error for &ChainError<T> {
# fn source(&self) -> Option<&(dyn Error + 'static)> {
# if let Some(ref e) = self.error_cause {
# Some(e.as_ref())
# } else {
# None
# }
# }
# }
#
# impl<T: 'static + Display + Debug> Error for &mut ChainError<T> {
# fn source(&self) -> Option<&(dyn Error + 'static)> {
# if let Some(ref e) = self.error_cause {
# Some(e.as_ref())
# } else {
# None
# }
# }
# }
#
# impl<T: 'static + Display + Debug> Display for ChainError<T> {
# fn fmt(&self, f: &mut Formatter) -> Result {
# write!(f, "{}", self.kind)?;
#
# #[cfg(feature = "display-cause")]
# {
# if let Some(e) = self.source() {
# writeln!(f, "\nCaused by:")?;
# Display::fmt(&e, f)?;
# }
# }
# Ok(())
# }
# }
#
# impl<T: 'static + Display + Debug> Debug for ChainError<T> {
# fn fmt(&self, f: &mut Formatter) -> Result {
# #[cfg(not(feature = "no-fileline"))]
# {
# if let Some(o) = self.occurrence {
# write!(f, "{}:{}: ", o.1, o.0)?;
# }
# }
#
# Debug::fmt(&self.kind, f)?;
#
# #[cfg(not(feature = "no-debug-cause"))]
# {
# if let Some(e) = self.source() {
# writeln!(f, "\nCaused by:")?;
# Debug::fmt(&e, f)?;
# }
# }
# Ok(())
# }
# }
#
# #[macro_export]
# macro_rules! cherr {
# ( $k:expr ) => {
# ChainError::<_>::new($k, None, Some((line!(), file!())))
# };
# ( $e:expr, $k:expr ) => {
# ChainError::<_>::new($k, Some(Box::from($e)), Some((line!(), file!())))
# };
# }
#
# #[macro_export]
# macro_rules! mstrerr {
# ( $t:ident, $v:expr $(, $more:expr)* ) => {
# |e| cherr!(e, $t (format!($v, $( $more , )* )))
# };
# ( $t:path, $v:expr $(, $more:expr)* ) => {
# |e| cherr!(e, $t (format!($v, $( $more , )* )))
# };
# ( $v:expr $(, $more:expr)* ) => {
# |e| cherr!(e, format!($v, $( $more , )* ))
# };
# }
#
# #[macro_export]
# macro_rules! derive_str_cherr {
# ($e:ident) => {
# struct $e(String);
# impl ::std::fmt::Display for $e {
# fn fmt(&self, f: &mut ::std::fmt::Formatter) -> ::std::fmt::Result {
# write!(f, "{}", self.0)
# }
# }
# impl ::std::fmt::Debug for $e {
# fn fmt(&self, f: &mut ::std::fmt::Formatter) -> ::std::fmt::Result {
# write!(f, "{}({})", stringify!($e), self.0)
# }
# }
# impl ::std::error::Error for $e {}
# };
# }
#
# #[macro_export]
# macro_rules! try_cherr_ref {
# ( $e:expr, $t:ident ) => {
# $e.downcast_ref::<ChainError<$t>>()
# };
# ( $e:expr, $t:path ) => {
# $e.downcast_ref::<ChainError<$t>>()
# };
# }
#
# #[macro_export]
# macro_rules! try_cherr_mut {
# ( $e:expr, $t:ident ) => {
# $e.downcast_mut::<ChainError<$t>>()
# };
# ( $e:expr, $t:path ) => {
# $e.downcast_mut::<ChainError<$t>>()
# };
# }
# }
</code></pre></pre>
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