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