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<head>
<!-- Book generated using mdBook -->
<meta charset="UTF-8">
<title>Chapter 1 - chainerror</title>
<title>chainerror - chainerror</title>
<meta content="text/html; charset=utf-8" http-equiv="Content-Type">
<meta name="description" content="">
<meta name="description" content="A tutorial for the chainerror rust crate.">
<meta name="viewport" content="width=device-width, initial-scale=1">
<meta name="theme-color" content="#ffffff" />
@ -75,7 +75,7 @@
</script>
<nav id="sidebar" class="sidebar" aria-label="Table of contents">
<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>
<ol class="chapter"><li class="affix"><a href="index.html">chainerror</a></li><li><a href="tutorial1.html"><strong aria-hidden="true">1.</strong> Simple String Errors</a></li><li><a href="tutorial2.html"><strong aria-hidden="true">2.</strong> Simple Chained String Errors</a></li><li><a href="tutorial3.html"><strong aria-hidden="true">3.</strong> Mapping Errors</a></li><li><a href="tutorial4.html"><strong aria-hidden="true">4.</strong> Saving coding chars</a></li><li><a href="tutorial5.html"><strong aria-hidden="true">5.</strong> The source() of Errors</a></li><li><a href="tutorial6.html"><strong aria-hidden="true">6.</strong> Downcast the Errors</a></li><li><a href="tutorial7.html"><strong aria-hidden="true">7.</strong> The root cause of all Errors</a></li><li><a href="tutorial8.html"><strong aria-hidden="true">8.</strong> Finding an Error cause</a></li><li><a href="tutorial9.html"><strong aria-hidden="true">9.</strong> Selective Error Handling</a></li><li><a href="tutorial10.html"><strong aria-hidden="true">10.</strong> ErrorKind to the rescue</a></li><li><a href="tutorial11.html"><strong aria-hidden="true">11.</strong> Debug for the ErrorKind</a></li><li class="affix"><a href="end.html">The End</a></li></ol>
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@ -140,37 +140,116 @@
<div id="content" class="content">
<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&lt;Error&gt;</code>.</p>
<p>As you can see by running the example (the &quot;Play&quot; 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;
<a class="header" href="#chainerror" id="chainerror"><h1>chainerror</h1></a>
<p><code>chainerror</code> provides an error backtrace like <code>failure</code> without doing a real backtrace, so even after you <code>strip</code> your
binaries, you still have the error backtrace.</p>
<p><code>chainerror</code> has no dependencies!</p>
<p><code>chainerror</code> uses <code>.source()</code> of <code>std::error::Error</code> along with <code>line()!</code> and <code>file()!</code> to provide a nice debug error backtrace.
It encapsulates all types, which have <code>Display + Debug</code> and can store the error cause internally.</p>
<p>Along with the <code>ChainError&lt;T&gt;</code> struct, <code>chainerror</code> comes with some useful helper macros to save a lot of typing.</p>
<p>Debug information is worth it!</p>
<p>Now continue reading the
<a href="https://haraldh.github.io/chainerror/tutorial1.html">Tutorial</a></p>
<a class="header" href="#example" id="example"><h2>Example:</h2></a>
<p>Output:</p>
<pre><code>$ cargo run -q --example example
Main Error Report: func1 error calling func2
Error reported by Func2Error: func2 error: calling func3
The root cause was: std::io::Error: Kind(
NotFound
)
Debug Error:
examples/example.rs:45: func1 error calling func2
Caused by:
examples/example.rs:20: Func2Error(func2 error: calling func3)
Caused by:
examples/example.rs:13: Error reading 'foo.txt'
Caused by:
Kind(NotFound)
</code></pre>
<pre><code class="language-rust ignore">use chainerror::*;
use std::error::Error;
use std::io;
use std::result::Result;
fn do_some_io() -&gt; Result&lt;(), Box&lt;Error&gt;&gt; {
Err(&quot;do_some_io error&quot;)?;
Err(io::Error::from(io::ErrorKind::NotFound))?;
Ok(())
}
fn func2() -&gt; Result&lt;(), Box&lt;Error&gt;&gt; {
if let Err(_) = do_some_io() {
Err(&quot;func2 error&quot;)?;
fn func3() -&gt; Result&lt;(), Box&lt;Error&gt;&gt; {
let filename = &quot;foo.txt&quot;;
do_some_io().map_err(mstrerr!(&quot;Error reading '{}'&quot;, filename))?;
Ok(())
}
derive_str_cherr!(Func2Error);
fn func2() -&gt; ChainResult&lt;(), Func2Error&gt; {
func3().map_err(mstrerr!(Func2Error, &quot;func2 error: calling func3&quot;))?;
Ok(())
}
enum Func1Error {
Func2,
IO(String),
}
impl ::std::fmt::Display for Func1Error {
fn fmt(&amp;self, f: &amp;mut ::std::fmt::Formatter) -&gt; ::std::fmt::Result {
match self {
Func1Error::Func2 =&gt; write!(f, &quot;func1 error calling func2&quot;),
Func1Error::IO(filename) =&gt; write!(f, &quot;Error reading '{}'&quot;, filename),
}
}
Ok(())
}
fn func1() -&gt; Result&lt;(), Box&lt;Error&gt;&gt; {
if let Err(_) = func2() {
Err(&quot;func1 error&quot;)?;
impl ::std::fmt::Debug for Func1Error {
fn fmt(&amp;self, f: &amp;mut ::std::fmt::Formatter) -&gt; ::std::fmt::Result {
write!(f, &quot;{}&quot;, self)
}
}
fn func1() -&gt; ChainResult&lt;(), Func1Error&gt; {
func2().map_err(|e| cherr!(e, Func1Error::Func2))?;
let filename = String::from(&quot;bar.txt&quot;);
do_some_io().map_err(|e| cherr!(e, Func1Error::IO(filename)))?;
Ok(())
}
fn main() -&gt; Result&lt;(), Box&lt;Error&gt;&gt; {
func1()
fn main() {
if let Err(e) = func1() {
match e.kind() {
Func1Error::Func2 =&gt; eprintln!(&quot;Main Error Report: func1 error calling func2&quot;),
Func1Error::IO(filename) =&gt; {
eprintln!(&quot;Main Error Report: func1 error reading '{}'&quot;, filename)
}
}
if let Some(e) = e.find_chain_cause::&lt;Func2Error&gt;() {
eprintln!(&quot;\nError reported by Func2Error: {}&quot;, e)
}
if let Some(e) = e.root_cause() {
let ioerror = e.downcast_ref::&lt;io::Error&gt;().unwrap();
eprintln!(&quot;\nThe root cause was: std::io::Error: {:#?}&quot;, ioerror);
}
eprintln!(&quot;\nDebug Error:\n{:?}&quot;, e);
}
}
</code></pre></pre>
</code></pre>
<a class="header" href="#features" id="features"><h2>Features</h2></a>
<p><code>no-fileline</code>
: completely turn off storing filename and line</p>
<p><code>display-cause</code>
: turn on printing a backtrace of the errors in <code>Display</code></p>
<p><code>no-debug-cause</code>
: turn off printing a backtrace of the errors in <code>Debug</code></p>
</main>
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