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<ol class="chapter"><li class="chapter-item expanded affix "><a href="index.html">chainerror</a></li><li class="chapter-item expanded "><a href="tutorial1.html"><strong aria-hidden="true">1.</strong> Simple String Errors</a></li><li class="chapter-item expanded "><a href="tutorial2.html"><strong aria-hidden="true">2.</strong> Simple Chained String Errors</a></li><li class="chapter-item expanded "><a href="tutorial3.html"><strong aria-hidden="true">3.</strong> Mapping Errors</a></li><li class="chapter-item expanded "><a href="tutorial4.html"><strong aria-hidden="true">4.</strong> More Information</a></li><li class="chapter-item expanded "><a href="tutorial5.html"><strong aria-hidden="true">5.</strong> The source() of Errors</a></li><li class="chapter-item expanded "><a href="tutorial6.html"><strong aria-hidden="true">6.</strong> Downcast the Errors</a></li><li class="chapter-item expanded "><a href="tutorial7.html"><strong aria-hidden="true">7.</strong> The root cause of all Errors</a></li><li class="chapter-item expanded "><a href="tutorial8.html"><strong aria-hidden="true">8.</strong> Finding an Error cause</a></li><li class="chapter-item expanded "><a href="tutorial9.html"><strong aria-hidden="true">9.</strong> Selective Error Handling</a></li><li class="chapter-item expanded "><a href="tutorial10.html"><strong aria-hidden="true">10.</strong> ErrorKind to the rescue</a></li><li class="chapter-item expanded "><a href="tutorial11.html"><strong aria-hidden="true">11.</strong> Debug for the ErrorKind</a></li><li class="chapter-item expanded "><a href="tutorial12.html"><strong aria-hidden="true">12.</strong> Deref for the ErrorKind</a></li><li class="chapter-item expanded "><a href="tutorial13.html"><strong aria-hidden="true">13.</strong> Writing a library</a></li><li class="chapter-item expanded "><a href="tutorial14.html" class="active"><strong aria-hidden="true">14.</strong> Going back to std</a></li><li class="chapter-item expanded affix "><a href="end.html">The End</a></li></ol>
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<h1><a class="header" href="#going-back-to-std" id="going-back-to-std">Going back to std</a></h1>
<p>Not using <code>chainerror</code> and going full <code>std</code> would look like this:</p>
<p>Btw, the code size is bigger than using <code>chainerror</code> :-)</p>
<pre><pre class="playground"><code class="language-rust">pub mod mycrate {
use std::error::Error as StdError;
use self::func2mod::{do_some_io, func2};
pub mod func2mod {
use std::error::Error as StdError;
use std::io;
pub enum ErrorKind {
IO(String),
}
impl std::fmt::Display for ErrorKind {
fn fmt(&self, f: &mut ::std::fmt::Formatter) -> std::fmt::Result {
match self {
ErrorKind::IO(s) => std::fmt::Display::fmt(s, f),
}
}
}
impl std::fmt::Debug for ErrorKind {
fn fmt(&self, f: &mut ::std::fmt::Formatter) -> std::fmt::Result {
match self {
ErrorKind::IO(s) => std::fmt::Display::fmt(s, f),
}
}
}
macro_rules! mcontext {
( $k:expr ) => {{
|e| {
Error(
$k,
Some(Box::from(e)),
Some(concat!(file!(), ":", line!(), ": ")),
)
}
}};
}
pub struct Error(
ErrorKind,
Option<Box<dyn std::error::Error + 'static>>,
Option<&'static str>,
);
impl Error {
pub fn kind(&self) -> &ErrorKind {
&self.0
}
}
impl From<ErrorKind> for Error {
fn from(e: ErrorKind) -> Self {
Error(e, None, None)
}
}
impl std::error::Error for Error {
fn source(&self) -> Option<&(dyn std::error::Error + 'static)> {
self.1.as_ref().map(|e| e.as_ref())
}
}
impl std::fmt::Display for Error {
fn fmt(&self, f: &mut std::fmt::Formatter) -> std::fmt::Result {
std::fmt::Display::fmt(&self.0, f)
}
}
impl std::fmt::Debug for Error {
fn fmt(&self, f: &mut std::fmt::Formatter) -> std::fmt::Result {
if let Some(ref o) = self.2 {
std::fmt::Display::fmt(o, f)?;
}
std::fmt::Debug::fmt(&self.0, f)?;
if let Some(e) = self.source() {
std::fmt::Display::fmt("\nCaused by:\n", f)?;
std::fmt::Debug::fmt(&e, f)?;
}
Ok(())
}
}
pub fn do_some_io() -> std::result::Result<(), Box<dyn std::error::Error>> {
Err(io::Error::from(io::ErrorKind::NotFound))?;
Ok(())
}
pub fn func2() -> std::result::Result<(), Error> {
let filename = "foo.txt";
do_some_io().map_err(mcontext!(ErrorKind::IO(format!(
"Error reading '{}'",
filename
))))?;
Ok(())
}
}
#[derive(Debug)]
pub enum ErrorKind {
Func2,
IO(String),
}
impl std::fmt::Display for ErrorKind {
fn fmt(&self, f: &mut ::std::fmt::Formatter) -> std::fmt::Result {
match self {
ErrorKind::Func2 => write!(f, "func1 error calling func2"),
ErrorKind::IO(filename) => write!(f, "Error reading '{}'", filename),
}
}
}
macro_rules! mcontext {
( $k:expr ) => {{
|e| {
Error(
$k,
Some(Box::from(e)),
Some(concat!(file!(), ":", line!(), ": ")),
)
}
}};
}
pub struct Error(
ErrorKind,
Option<Box<dyn std::error::Error + 'static>>,
Option<&'static str>,
);
impl Error {
pub fn kind(&self) -> &ErrorKind {
&self.0
}
}
impl From<ErrorKind> for Error {
fn from(e: ErrorKind) -> Self {
Error(e, None, None)
}
}
impl std::error::Error for Error {
fn source(&self) -> Option<&(dyn std::error::Error + 'static)> {
self.1.as_ref().map(|e| e.as_ref())
}
}
impl std::fmt::Display for Error {
fn fmt(&self, f: &mut std::fmt::Formatter) -> std::fmt::Result {
std::fmt::Display::fmt(&self.0, f)
}
}
impl std::fmt::Debug for Error {
fn fmt(&self, f: &mut std::fmt::Formatter) -> std::fmt::Result {
if let Some(ref o) = self.2 {
std::fmt::Display::fmt(o, f)?;
}
std::fmt::Debug::fmt(&self.0, f)?;
if let Some(e) = self.source() {
std::fmt::Display::fmt("\nCaused by:\n", f)?;
std::fmt::Debug::fmt(&e, f)?;
}
Ok(())
}
}
pub type Result<T> = std::result::Result<T, Error>;
pub fn func1() -> Result<()> {
func2().map_err(mcontext!(ErrorKind::Func2))?;
let filename = String::from("bar.txt");
do_some_io().map_err(mcontext!(ErrorKind::IO(filename)))?;
Ok(())
}
}
fn main() -> Result<(), Box<dyn std::error::Error + Send + Sync>> {
use mycrate::func1;
use mycrate::ErrorKind;
use std::error::Error;
use std::io;
if let Err(e) = func1() {
match e.kind() {
ErrorKind::Func2 => eprintln!("Main Error Report: func1 error calling func2"),
ErrorKind::IO(ref filename) => {
eprintln!("Main Error Report: func1 error reading '{}'", filename)
}
}
eprintln!();
let mut s: &dyn Error = &e;
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;
}
eprintln!("\nDebug Error:\n{:?}", e);
std::process::exit(1);
}
Ok(())
}
</code></pre></pre>
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