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<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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<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<T></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() -> Result<(), Box<Error>> {
Err(io::Error::from(io::ErrorKind::NotFound))?;
Ok(())
}
fn func3() -> Result<(), Box<Error>> {
let filename = "foo.txt";
do_some_io().map_err(mstrerr!("Error reading '{}'", filename))?;
Ok(())
}
derive_str_cherr!(Func2Error);
fn func2() -> ChainResult<(), Func2Error> {
func3().map_err(mstrerr!(Func2Error, "func2 error: calling func3"))?;
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() {
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!("\nError reported by Func2Error: {}", e)
}
if let Some(e) = e.root_cause() {
let ioerror = e.downcast_ref::<io::Error>().unwrap();
eprintln!("\nThe root cause was: std::io::Error: {:#?}", ioerror);
}
eprintln!("\nDebug Error:\n{:?}", e);
}
}
</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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