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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"><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="#chainerror" id="chainerror">chainerror</a></h1>
|
|
<p><a href="https://travis-ci.org/haraldh/chainerror"><img src="https://travis-ci.org/haraldh/chainerror.svg?branch=master" alt="Build Status" /></a>
|
|
<a href="https://crates.io/crates/chainerror"><img src="https://img.shields.io/crates/v/chainerror.svg" alt="Crate" /></a>
|
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<a href="https://docs.rs/chainerror/"><img src="https://img.shields.io/badge/api-rustdoc-blue.svg" alt="Rust Documentation" /></a></p>
|
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<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>
|
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<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>
|
|
<h2><a class="header" href="#example" id="example">Example:</a></h2>
|
|
<p>Output:</p>
|
|
<pre><code>$ cargo run -q --example example
|
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Main Error Report: func1 error calling func2
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|
|
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Error reported by Func2Error: func2 error: calling func3
|
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|
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The root cause was: std::io::Error: Kind(
|
|
NotFound
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|
)
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Debug Error:
|
|
examples/example.rs:45: func1 error calling func2
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Caused by:
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|
examples/example.rs:20: Func2Error(func2 error: calling func3)
|
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Caused by:
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examples/example.rs:13: Error reading 'foo.txt'
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|
Caused by:
|
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Kind(NotFound)
|
|
</code></pre>
|
|
<pre><code class="language-rust ignore">use chainerror::*;
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|
use std::error::Error;
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|
use std::io;
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use std::result::Result;
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|
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fn do_some_io() -> Result<(), Box<Error + Send + Sync>> {
|
|
Err(io::Error::from(io::ErrorKind::NotFound))?;
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|
Ok(())
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|
}
|
|
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fn func3() -> Result<(), Box<Error + Send + Sync>> {
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|
let filename = "foo.txt";
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|
do_some_io().map_err(mstrerr!("Error reading '{}'", filename))?;
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Ok(())
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}
|
|
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derive_str_cherr!(Func2Error);
|
|
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fn func2() -> ChainResult<(), Func2Error> {
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|
func3().map_err(mstrerr!(Func2Error, "func2 error: calling func3"))?;
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Ok(())
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|
}
|
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|
enum Func1Error {
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|
Func2,
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|
IO(String),
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|
}
|
|
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impl ::std::fmt::Display for Func1Error {
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|
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);
|
|
}
|
|
|
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eprintln!("\nDebug Error:\n{:?}", e);
|
|
}
|
|
}
|
|
|
|
</code></pre>
|
|
<h2><a class="header" href="#features" id="features">Features</a></h2>
|
|
<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>
|
|
<h1><a class="header" href="#simple-string-errors" id="simple-string-errors">Simple String Errors</a></h1>
|
|
<p>An easy way of doing error handling in rust is by returning <code>String</code> as a <code>Box<std::error::Error></code>.</p>
|
|
<p>If the rust <code>main</code> function returns an <code>Err()</code>, this <code>Err()</code> will be displayed with <code>std::fmt::Debug</code>.</p>
|
|
<p>As you can see by running the example (by pressing the "Play" button in upper right of the code block),
|
|
this only
|
|
prints out the last <code>Error</code>.</p>
|
|
<pre><code>Error: StringError("func1 error")
|
|
</code></pre>
|
|
<p>The next chapters of this tutorial show how <code>chainerror</code> adds more information
|
|
and improves inspecting the sources of an error.</p>
|
|
<p>You can also run the tutorial examples in the checked out
|
|
<a href="https://github.com/haraldh/chainerror">chainerror git repo</a>.</p>
|
|
<pre><code>$ cargo run -q --example tutorial1
|
|
</code></pre>
|
|
<pre><pre class="playpen"><code class="language-rust">use std::error::Error;
|
|
use std::io;
|
|
use std::result::Result;
|
|
|
|
fn do_some_io() -> Result<(), Box<Error + Send + Sync>> {
|
|
Err(io::Error::from(io::ErrorKind::NotFound))?;
|
|
Ok(())
|
|
}
|
|
|
|
fn func2() -> Result<(), Box<Error + Send + Sync>> {
|
|
if let Err(_) = do_some_io() {
|
|
Err("func2 error")?;
|
|
}
|
|
Ok(())
|
|
}
|
|
|
|
fn func1() -> Result<(), Box<Error + Send + Sync>> {
|
|
if let Err(_) = func2() {
|
|
Err("func1 error")?;
|
|
}
|
|
Ok(())
|
|
}
|
|
|
|
fn main() -> Result<(), Box<Error + Send + Sync>> {
|
|
func1()
|
|
}
|
|
</code></pre></pre>
|
|
<h1><a class="header" href="#simple-chained-string-errors" id="simple-chained-string-errors">Simple Chained String Errors</a></h1>
|
|
<p>With relatively small changes and the help of the <code>cherr!</code> macro of the <code>chainerror</code> crate
|
|
the <code>String</code> errors are now chained together.</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 chainerror::*;
|
|
|
|
use std::error::Error;
|
|
use std::io;
|
|
use std::result::Result;
|
|
|
|
fn do_some_io() -> Result<(), Box<Error + Send + Sync>> {
|
|
Err(io::Error::from(io::ErrorKind::NotFound))?;
|
|
Ok(())
|
|
}
|
|
|
|
fn func2() -> Result<(), Box<Error + Send + Sync>> {
|
|
if let Err(e) = do_some_io() {
|
|
Err(cherr!(e, "func2 error"))?;
|
|
}
|
|
Ok(())
|
|
}
|
|
|
|
fn func1() -> Result<(), Box<Error + Send + Sync>> {
|
|
if let Err(e) = func2() {
|
|
Err(cherr!(e, "func1 error"))?;
|
|
}
|
|
Ok(())
|
|
}
|
|
|
|
fn main() -> Result<(), Box<Error + Send + Sync>> {
|
|
func1()
|
|
}
|
|
<span class="boring">#[allow(dead_code)]
|
|
</span><span class="boring">mod chainerror {
|
|
</span>{{#includecomment ../src/lib.rs}}
|
|
<span class="boring">}
|
|
</span></code></pre></pre>
|
|
<h3><a class="header" href="#what-did-we-do-here" id="what-did-we-do-here">What did we do here?</a></h3>
|
|
<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!(olderror, newerror)</code> stores <code>olderror</code> as the source/cause of <code>newerror</code>
|
|
along with the filename (<code>file!()</code>) and line number (<code>line!()</code>)
|
|
and returns <code>newerror</code>.</p>
|
|
<p><code>Err()?</code> then returns the inner error applying <code>.into()</code>, so that we
|
|
again have a <code>Err(Box<Error + Send + Sync>)</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> in our case is <code>ChainError<String></code>.</p>
|
|
<h1><a class="header" href="#mapping-errors" id="mapping-errors">Mapping Errors</a></h1>
|
|
<p>Now let's get more rust idiomatic by using <code>.map_err()</code>.</p>
|
|
<pre><pre class="playpen"><code class="language-rust">use chainerror::*;
|
|
|
|
use std::error::Error;
|
|
use std::io;
|
|
use std::result::Result;
|
|
|
|
fn do_some_io() -> Result<(), Box<Error + Send + Sync>> {
|
|
Err(io::Error::from(io::ErrorKind::NotFound))?;
|
|
Ok(())
|
|
}
|
|
|
|
fn func2() -> Result<(), Box<Error + Send + Sync>> {
|
|
do_some_io().map_err(|e| cherr!(e, "func2 error"))?;
|
|
Ok(())
|
|
}
|
|
|
|
fn func1() -> Result<(), Box<Error + Send + Sync>> {
|
|
func2().map_err(|e| cherr!(e, "func1 error"))?;
|
|
Ok(())
|
|
}
|
|
|
|
fn main() -> Result<(), Box<Error + Send + Sync>> {
|
|
if let Err(e) = func1() {
|
|
eprintln!("{:?}", e);
|
|
}
|
|
Ok(())
|
|
}
|
|
<span class="boring">#[allow(dead_code)]
|
|
</span><span class="boring">mod chainerror {
|
|
</span>{{#includecomment ../src/lib.rs}}
|
|
<span class="boring">}
|
|
</span></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>
|
|
<h1><a class="header" href="#saving-coding-chars" id="saving-coding-chars">Saving coding chars</a></h1>
|
|
<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 chainerror::*;
|
|
use std::error::Error;
|
|
use std::io;
|
|
use std::result::Result;
|
|
|
|
fn do_some_io() -> Result<(), Box<Error + Send + Sync>> {
|
|
Err(io::Error::from(io::ErrorKind::NotFound))?;
|
|
Ok(())
|
|
}
|
|
|
|
fn func2() -> Result<(), Box<Error + Send + Sync>> {
|
|
let filename = "foo.txt";
|
|
do_some_io().map_err(mstrerr!("Error reading '{}'", filename))?;
|
|
Ok(())
|
|
}
|
|
|
|
fn func1() -> Result<(), Box<Error + Send + Sync>> {
|
|
func2().map_err(mstrerr!("func1 error"))?;
|
|
Ok(())
|
|
}
|
|
|
|
fn main() -> Result<(), Box<Error + Send + Sync>> {
|
|
if let Err(e) = func1() {
|
|
eprintln!("{:?}", e);
|
|
}
|
|
Ok(())
|
|
}
|
|
<span class="boring">#[allow(dead_code)]
|
|
</span><span class="boring">mod chainerror {
|
|
</span>{{#includecomment ../src/lib.rs}}
|
|
<span class="boring">}
|
|
</span></code></pre></pre>
|
|
<h1><a class="header" href="#the-source-of-errors" id="the-source-of-errors">The source() of Errors</a></h1>
|
|
<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 chainerror::*;
|
|
use std::error::Error;
|
|
use std::io;
|
|
use std::result::Result;
|
|
|
|
fn do_some_io() -> Result<(), Box<Error + Send + Sync>> {
|
|
Err(io::Error::from(io::ErrorKind::NotFound))?;
|
|
Ok(())
|
|
}
|
|
|
|
fn func2() -> Result<(), Box<Error + Send + Sync>> {
|
|
let filename = "foo.txt";
|
|
do_some_io().map_err(mstrerr!("Error reading '{}'", filename))?;
|
|
Ok(())
|
|
}
|
|
|
|
fn func1() -> Result<(), Box<Error + Send + Sync>> {
|
|
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 + Send + Sync>> {
|
|
if let Err(e) = func1() {
|
|
eprintln!("{}", e);
|
|
}
|
|
Ok(())
|
|
}
|
|
<span class="boring">#[allow(dead_code)]
|
|
</span><span class="boring">mod chainerror {
|
|
</span>{{#includecomment ../src/lib.rs}}
|
|
<span class="boring">}
|
|
</span></code></pre></pre>
|
|
<p>Note, that because we changed the output of the error in <code>main()</code> from
|
|
<code>Debug</code> to <code>Display</code>, 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>
|
|
<h1><a class="header" href="#downcast-the-errors" id="downcast-the-errors">Downcast the Errors</a></h1>
|
|
<p><code>std::error::Error</code> comes with some helper methods to get to the original object of the
|
|
<code>&(dyn Error + 'static)</code> returned by <code>.source()</code>.</p>
|
|
<pre><code class="language-rust ignore">pub fn downcast_ref<T: Error + 'static>(&self) -> Option<&T>
|
|
pub fn downcast_mut<T: Error + 'static>(&mut self) -> Option<&mut T>
|
|
</code></pre>
|
|
<p>This is how it looks like, when using those:</p>
|
|
<pre><pre class="playpen"><code class="language-rust">use chainerror::*;
|
|
use std::error::Error;
|
|
use std::io;
|
|
use std::result::Result;
|
|
|
|
fn do_some_io() -> Result<(), Box<Error + Send + Sync>> {
|
|
Err(io::Error::from(io::ErrorKind::NotFound))?;
|
|
Ok(())
|
|
}
|
|
|
|
fn func2() -> Result<(), Box<Error + Send + Sync>> {
|
|
let filename = "foo.txt";
|
|
do_some_io().map_err(mstrerr!("Error reading '{}'", filename))?;
|
|
Ok(())
|
|
}
|
|
|
|
fn func1() -> Result<(), Box<Error + Send + Sync>> {
|
|
func2().map_err(mstrerr!("func1 error"))?;
|
|
Ok(())
|
|
}
|
|
|
|
fn main() -> Result<(), Box<Error + Send + Sync>> {
|
|
if let Err(e) = func1() {
|
|
eprintln!("Error: {}", e);
|
|
let mut s : &(dyn Error) = 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(())
|
|
}
|
|
<span class="boring">#[allow(dead_code)]
|
|
</span><span class="boring">mod chainerror {
|
|
</span>{{#includecomment ../src/lib.rs}}
|
|
<span class="boring">}
|
|
</span></code></pre></pre>
|
|
<h1><a class="header" href="#the-root-cause-of-all-errors" id="the-root-cause-of-all-errors">The root cause of all Errors</a></h1>
|
|
<p><code>chainerror</code> also has some helper methods:</p>
|
|
<pre><code class="language-rust ignore">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>>
|
|
fn root_cause(&self) -> Option<&(dyn Error + 'static)>
|
|
fn find_cause<U: Error + 'static>(&self) -> Option<&U>
|
|
fn find_chain_cause<U: Error + 'static>(&self) -> Option<&ChainError<U>>
|
|
fn kind<'a>(&'a self) -> &'a T
|
|
</code></pre>
|
|
<p>Using <code>downcast_chain_ref::<String>()</code> gives a <code>ChainError<String></code>, which can be used
|
|
to call <code>.find_cause::<io::Error>()</code>. </p>
|
|
<pre><code class="language-rust ignore"> if let Some(s) = e.downcast_chain_ref::<String>() {
|
|
if let Some(ioerror) = s.find_cause::<io::Error>() {
|
|
</code></pre>
|
|
<p>or to use <code>.root_cause()</code>, which of course can be of any type implementing <code>std::error::Error</code>.</p>
|
|
<pre><code class="language-rust ignore"> if let Some(e) = s.root_cause() {
|
|
</code></pre>
|
|
<pre><pre class="playpen"><code class="language-rust">use chainerror::*;
|
|
use std::error::Error;
|
|
use std::io;
|
|
use std::result::Result;
|
|
|
|
fn do_some_io() -> Result<(), Box<Error + Send + Sync>> {
|
|
Err(io::Error::from(io::ErrorKind::NotFound))?;
|
|
Ok(())
|
|
}
|
|
|
|
fn func2() -> Result<(), Box<Error + Send + Sync>> {
|
|
let filename = "foo.txt";
|
|
do_some_io().map_err(mstrerr!("Error reading '{}'", filename))?;
|
|
Ok(())
|
|
}
|
|
|
|
fn func1() -> Result<(), Box<Error + Send + Sync>> {
|
|
func2().map_err(mstrerr!("func1 error"))?;
|
|
Ok(())
|
|
}
|
|
|
|
fn main() -> Result<(), Box<Error + Send + Sync>> {
|
|
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(())
|
|
}
|
|
<span class="boring">#[allow(dead_code)]
|
|
</span><span class="boring">mod chainerror {
|
|
</span>{{#includecomment ../src/lib.rs}}
|
|
<span class="boring">}
|
|
</span></code></pre></pre>
|
|
<h1><a class="header" href="#finding-an-error-cause" id="finding-an-error-cause">Finding an Error cause</a></h1>
|
|
<p>To distinguish the errors occuring in various places, we can define named string errors with the
|
|
"new type" pattern.</p>
|
|
<pre><code class="language-rust ignore">derive_str_cherr!(Func2Error);
|
|
derive_str_cherr!(Func1Error);
|
|
</code></pre>
|
|
<p>Instead of <code>ChainError<String></code> we now have <code>struct Func1Error(String)</code> and <code>ChainError<Func1Error></code>.</p>
|
|
<p>In the <code>main</code> function you can see, how we can match the different errors.</p>
|
|
<p>Also see:</p>
|
|
<pre><code class="language-rust ignore"> if let Some(f2err) = f1err.find_chain_cause::<Func2Error>() {
|
|
</code></pre>
|
|
<p>as a shortcut to</p>
|
|
<pre><code class="language-rust ignore"> if let Some(f2err) = f1err.find_cause::<ChainError<Func2Error>>() {
|
|
</code></pre>
|
|
<p>hiding the <code>ChainError<T></code> implementation detail.</p>
|
|
<pre><pre class="playpen"><code class="language-rust">use chainerror::*;
|
|
use std::error::Error;
|
|
use std::io;
|
|
use std::result::Result;
|
|
|
|
fn do_some_io() -> Result<(), Box<Error + Send + Sync>> {
|
|
Err(io::Error::from(io::ErrorKind::NotFound))?;
|
|
Ok(())
|
|
}
|
|
|
|
derive_str_cherr!(Func2Error);
|
|
|
|
fn func2() -> Result<(), Box<Error + Send + Sync>> {
|
|
let filename = "foo.txt";
|
|
do_some_io().map_err(mstrerr!(Func2Error, "Error reading '{}'", filename))?;
|
|
Ok(())
|
|
}
|
|
|
|
derive_str_cherr!(Func1Error);
|
|
|
|
fn func1() -> Result<(), Box<Error + Send + Sync>> {
|
|
func2().map_err(mstrerr!(Func1Error, "func1 error"))?;
|
|
Ok(())
|
|
}
|
|
|
|
fn main() -> Result<(), Box<Error + Send + Sync>> {
|
|
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(())
|
|
}
|
|
<span class="boring">#[allow(dead_code)]
|
|
</span><span class="boring">mod chainerror {
|
|
</span>{{#includecomment ../src/lib.rs}}
|
|
<span class="boring">}
|
|
</span></code></pre></pre>
|
|
<h1><a class="header" href="#selective-error-handling" id="selective-error-handling">Selective Error Handling</a></h1>
|
|
<p>What about functions returning different Error types?</p>
|
|
<p>In this example <code>func1()</code> can return either <code>Func1ErrorFunc2</code> or <code>Func1ErrorIO</code>.</p>
|
|
<p>We might want to <code>match</code> on <code>func1()</code> with something like:</p>
|
|
<pre><code class="language-rust ignore">fn main() -> Result<(), Box<Error + Send + Sync>> {
|
|
match func1() {
|
|
Err(e) if let Some(s) = e.downcast_chain_ref::<Func1ErrorIO>() =>
|
|
eprintln!("Func1ErrorIO:\n{:?}", s),
|
|
|
|
Err(e) if let Some(s) = e.downcast_chain_ref::<Func1ErrorFunc2>() =>
|
|
eprintln!("Func1ErrorFunc2:\n{:?}", s),
|
|
|
|
Ok(_) => {},
|
|
}
|
|
Ok(())
|
|
}
|
|
</code></pre>
|
|
<p>but this is not valid rust code, so we end up doing it the hard way.
|
|
In the next chapter, we will see, how to solve this more elegantly.</p>
|
|
<pre><pre class="playpen"><code class="language-rust">use chainerror::*;
|
|
use std::error::Error;
|
|
use std::io;
|
|
use std::result::Result;
|
|
|
|
fn do_some_io() -> Result<(), Box<Error + Send + Sync>> {
|
|
Err(io::Error::from(io::ErrorKind::NotFound))?;
|
|
Ok(())
|
|
}
|
|
|
|
derive_str_cherr!(Func2Error);
|
|
|
|
fn func2() -> Result<(), Box<Error + Send + Sync>> {
|
|
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 + Send + Sync>> {
|
|
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 + Send + Sync>> {
|
|
if let Err(e) = func1() {
|
|
if let Some(s) = e.downcast_ref::<ChainError<Func1ErrorIO>>() {
|
|
eprintln!("Func1ErrorIO:\n{:?}", s);
|
|
}
|
|
|
|
if let Some(s) = e.downcast_chain_ref::<Func1ErrorFunc2>() {
|
|
eprintln!("Func1ErrorFunc2:\n{:?}", s);
|
|
}
|
|
}
|
|
Ok(())
|
|
}
|
|
<span class="boring">#[allow(dead_code)]
|
|
</span><span class="boring">mod chainerror {
|
|
</span>{{#includecomment ../src/lib.rs}}
|
|
<span class="boring">}
|
|
</span></code></pre></pre>
|
|
<h1><a class="header" href="#errorkind-to-the-rescue" id="errorkind-to-the-rescue">ErrorKind to the rescue</a></h1>
|
|
<p>To cope with different kind of errors, we introduce the kind of an error <code>Func1ErrorKind</code> with an enum.</p>
|
|
<p>Because we derive <code>Debug</code> and implement <code>Display</code> our <code>Func1ErrorKind</code> enum, this enum can be used as
|
|
a <code>std::error::Error</code>.</p>
|
|
<p>Not using <code>String</code> errors anymore, the <code>cherr!()</code> macro seen in the beginning of
|
|
the tutorial has to be used again.</p>
|
|
<p>Only returning <code>Func1ErrorKind</code> in <code>func1()</code> now let us get rid of <code>Result<(), Box<Error + Send + Sync>></code> and we can
|
|
use <code>ChainResult<(), Func1ErrorKind></code>.</p>
|
|
<p>In <code>main</code> we can now directly use the methods of <code>ChainError<T></code> without downcasting the error first.</p>
|
|
<p>Also a nice <code>match</code> on <code>ChainError<T>.kind()</code> is now possible, which returns <code>&T</code>, meaning
|
|
<code>&Func1ErrorKind</code> here.</p>
|
|
<pre><pre class="playpen"><code class="language-rust">use chainerror::*;
|
|
use std::error::Error;
|
|
use std::io;
|
|
use std::result::Result;
|
|
|
|
fn do_some_io() -> Result<(), Box<Error + Send + Sync>> {
|
|
Err(io::Error::from(io::ErrorKind::NotFound))?;
|
|
Ok(())
|
|
}
|
|
|
|
derive_str_cherr!(Func2Error);
|
|
|
|
fn func2() -> Result<(), Box<Error + Send + Sync>> {
|
|
let filename = "foo.txt";
|
|
do_some_io().map_err(mstrerr!(Func2Error, "Error reading '{}'", filename))?;
|
|
Ok(())
|
|
}
|
|
|
|
#[derive(Debug)]
|
|
enum Func1ErrorKind {
|
|
Func2,
|
|
IO(String),
|
|
}
|
|
|
|
impl ::std::fmt::Display for Func1ErrorKind {
|
|
fn fmt(&self, f: &mut ::std::fmt::Formatter) -> ::std::fmt::Result {
|
|
match self {
|
|
Func1ErrorKind::Func2 => write!(f, "func1 error calling func2"),
|
|
Func1ErrorKind::IO(filename) => write!(f, "Error reading '{}'", filename),
|
|
}
|
|
}
|
|
}
|
|
impl ::std::error::Error for Func1ErrorKind {}
|
|
|
|
fn func1() -> ChainResult<(), Func1ErrorKind> {
|
|
func2().map_err(|e| cherr!(e, Func1ErrorKind::Func2))?;
|
|
let filename = String::from("bar.txt");
|
|
do_some_io().map_err(|e| cherr!(e, Func1ErrorKind::IO(filename)))?;
|
|
Ok(())
|
|
}
|
|
|
|
fn main() -> Result<(), Box<Error + Send + Sync>> {
|
|
if let Err(e) = func1() {
|
|
match e.kind() {
|
|
Func1ErrorKind::Func2 => eprintln!("Main Error Report: func1 error calling func2"),
|
|
Func1ErrorKind::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)
|
|
}
|
|
|
|
eprintln!("\nDebug Error:\n{:?}", e);
|
|
}
|
|
Ok(())
|
|
}
|
|
<span class="boring">#[allow(dead_code)]
|
|
</span><span class="boring">mod chainerror {
|
|
</span>{{#includecomment ../src/lib.rs}}
|
|
<span class="boring">}
|
|
</span></code></pre></pre>
|
|
<h1><a class="header" href="#debug-for-the-errorkind" id="debug-for-the-errorkind">Debug for the ErrorKind</a></h1>
|
|
<p>One small improvement at the end of the tutorial is to fix the debug output of
|
|
<code>Func1ErrorKind</code>. As you probably noticed, the output doesn't say much of the enum.</p>
|
|
<pre><code>Debug Error:
|
|
src/main.rs:35: Func2
|
|
[…]
|
|
</code></pre>
|
|
<p>As a lazy shortcut, we implement <code>Debug</code> by calling <code>Display</code> and end up with</p>
|
|
<pre><code>Debug Error:
|
|
src/main.rs:40: func1 error calling func2
|
|
[…}
|
|
</code></pre>
|
|
<p>which gives us a lot more detail.</p>
|
|
<p>To create your own Errors, you might find <a href="https://crates.io">crates</a> which create enum <code>Display+Debug</code> via derive macros.</p>
|
|
<p>Also noteworthy is <a href="https://crates.io/crates/custom_error">custom_error</a> to define your custom errors,
|
|
which can then be used with <code>chainerror</code>.</p>
|
|
<pre><pre class="playpen"><code class="language-rust">use chainerror::*;
|
|
use std::error::Error;
|
|
use std::io;
|
|
use std::result::Result;
|
|
|
|
fn do_some_io() -> Result<(), Box<Error + Send + Sync>> {
|
|
Err(io::Error::from(io::ErrorKind::NotFound))?;
|
|
Ok(())
|
|
}
|
|
|
|
derive_str_cherr!(Func2Error);
|
|
|
|
fn func2() -> Result<(), Box<Error + Send + Sync>> {
|
|
let filename = "foo.txt";
|
|
do_some_io().map_err(mstrerr!(Func2Error, "Error reading '{}'", filename))?;
|
|
Ok(())
|
|
}
|
|
|
|
enum Func1ErrorKind {
|
|
Func2,
|
|
IO(String),
|
|
}
|
|
|
|
impl ::std::fmt::Display for Func1ErrorKind {
|
|
fn fmt(&self, f: &mut ::std::fmt::Formatter) -> ::std::fmt::Result {
|
|
match self {
|
|
Func1ErrorKind::Func2 => write!(f, "func1 error calling func2"),
|
|
Func1ErrorKind::IO(filename) => write!(f, "Error reading '{}'", filename),
|
|
}
|
|
}
|
|
}
|
|
|
|
impl ::std::fmt::Debug for Func1ErrorKind {
|
|
fn fmt(&self, f: &mut ::std::fmt::Formatter) -> ::std::fmt::Result {
|
|
write!(f, "{}", self)
|
|
}
|
|
}
|
|
|
|
impl ::std::error::Error for Func1ErrorKind {}
|
|
|
|
fn func1() -> ChainResult<(), Func1ErrorKind> {
|
|
func2().map_err(|e| cherr!(e, Func1ErrorKind::Func2))?;
|
|
let filename = String::from("bar.txt");
|
|
do_some_io().map_err(|e| cherr!(e, Func1ErrorKind::IO(filename)))?;
|
|
Ok(())
|
|
}
|
|
|
|
fn main() -> Result<(), Box<Error + Send + Sync>> {
|
|
if let Err(e) = func1() {
|
|
match e.kind() {
|
|
Func1ErrorKind::Func2 => eprintln!("Main Error Report: func1 error calling func2"),
|
|
Func1ErrorKind::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)
|
|
}
|
|
|
|
eprintln!("\nDebug Error:\n{:?}", e);
|
|
}
|
|
Ok(())
|
|
}
|
|
<span class="boring">#[allow(dead_code)]
|
|
</span><span class="boring">mod chainerror {
|
|
</span>{{#includecomment ../src/lib.rs}}
|
|
<span class="boring">}
|
|
</span></code></pre></pre>
|
|
<h1><a class="header" href="#deref-for-the-errorkind" id="deref-for-the-errorkind">Deref for the ErrorKind</a></h1>
|
|
<p>Because ChainError<T> implements Deref to &T, we can also match on <code>*e</code> instead of <code>e.kind()</code>
|
|
or call a function with <code>&e</code></p>
|
|
<pre><pre class="playpen"><code class="language-rust">use chainerror::*;
|
|
use std::error::Error;
|
|
use std::io;
|
|
use std::result::Result;
|
|
|
|
fn do_some_io() -> Result<(), Box<Error + Send + Sync>> {
|
|
Err(io::Error::from(io::ErrorKind::NotFound))?;
|
|
Ok(())
|
|
}
|
|
|
|
derive_str_cherr!(Func2Error);
|
|
|
|
fn func2() -> Result<(), Box<Error + Send + Sync>> {
|
|
let filename = "foo.txt";
|
|
do_some_io().map_err(mstrerr!(Func2Error, "Error reading '{}'", filename))?;
|
|
Ok(())
|
|
}
|
|
|
|
enum Func1ErrorKind {
|
|
Func2,
|
|
IO(String),
|
|
}
|
|
|
|
impl ::std::fmt::Display for Func1ErrorKind {
|
|
fn fmt(&self, f: &mut ::std::fmt::Formatter) -> ::std::fmt::Result {
|
|
match self {
|
|
Func1ErrorKind::Func2 => write!(f, "func1 error calling func2"),
|
|
Func1ErrorKind::IO(filename) => write!(f, "Error reading '{}'", filename),
|
|
}
|
|
}
|
|
}
|
|
|
|
impl ::std::fmt::Debug for Func1ErrorKind {
|
|
fn fmt(&self, f: &mut ::std::fmt::Formatter) -> ::std::fmt::Result {
|
|
write!(f, "{}", self)
|
|
}
|
|
}
|
|
|
|
impl ::std::error::Error for Func1ErrorKind {}
|
|
|
|
fn func1() -> ChainResult<(), Func1ErrorKind> {
|
|
func2().map_err(|e| cherr!(e, Func1ErrorKind::Func2))?;
|
|
let filename = String::from("bar.txt");
|
|
do_some_io().map_err(|e| cherr!(e, Func1ErrorKind::IO(filename)))?;
|
|
Ok(())
|
|
}
|
|
|
|
fn handle_func1errorkind(e: &Func1ErrorKind) {
|
|
match e {
|
|
Func1ErrorKind::Func2 => eprintln!("Main Error Report: func1 error calling func2"),
|
|
Func1ErrorKind::IO(ref filename) => {
|
|
eprintln!("Main Error Report: func1 error reading '{}'", filename)
|
|
}
|
|
}
|
|
}
|
|
|
|
fn main() -> Result<(), Box<Error + Send + Sync>> {
|
|
if let Err(e) = func1() {
|
|
match *e {
|
|
Func1ErrorKind::Func2 => eprintln!("Main Error Report: func1 error calling func2"),
|
|
Func1ErrorKind::IO(ref filename) => {
|
|
eprintln!("Main Error Report: func1 error reading '{}'", filename)
|
|
}
|
|
}
|
|
|
|
handle_func1errorkind(&e);
|
|
|
|
if let Some(e) = e.find_chain_cause::<Func2Error>() {
|
|
eprintln!("\nError reported by Func2Error: {}", e)
|
|
}
|
|
|
|
eprintln!("\nDebug Error:\n{:?}", e);
|
|
}
|
|
Ok(())
|
|
}
|
|
<span class="boring">#[allow(dead_code)]
|
|
</span><span class="boring">mod chainerror {
|
|
</span>{{#includecomment ../src/lib.rs}}
|
|
<span class="boring">}
|
|
</span></code></pre></pre>
|
|
<h1><a class="header" href="#writing-a-library" id="writing-a-library">Writing a library</a></h1>
|
|
<p>I would advise to only expose an <code>mycrate::ErrorKind</code> and type alias <code>mycrate::Error</code> to <code>ChainError<mycrate::ErrorKind></code>
|
|
so you can tell your library users to use the <code>.kind()</code> method as <code>std::io::Error</code> does.</p>
|
|
<p>If you later decide to make your own <code>Error</code> implementation, your library users don't
|
|
have to change much or anything.</p>
|
|
<pre><pre class="playpen"><code class="language-rust"><span class="boring">#[allow(dead_code)]
|
|
</span><span class="boring">#[macro_use]
|
|
</span><span class="boring">pub mod chainerror {
|
|
</span>{{#includecomment ../src/lib.rs}}
|
|
<span class="boring">}
|
|
</span>pub mod mycrate {
|
|
use crate::chainerror::*; // omit the `crate::` part
|
|
use std::io;
|
|
|
|
fn do_some_io() -> std::result::Result<(), Box<std::error::Error + Send + Sync>> {
|
|
Err(io::Error::from(io::ErrorKind::NotFound))?;
|
|
Ok(())
|
|
}
|
|
|
|
derive_str_cherr!(Func2Error);
|
|
|
|
fn func2() -> std::result::Result<(), Box<std::error::Error + Send + Sync>> {
|
|
let filename = "foo.txt";
|
|
do_some_io().map_err(mstrerr!(Func2Error, "Error reading '{}'", filename))?;
|
|
Ok(())
|
|
}
|
|
|
|
#[derive(Debug, Clone)]
|
|
pub enum ErrorKind {
|
|
Func2,
|
|
IO(String),
|
|
}
|
|
|
|
derive_err_kind!(Error, ErrorKind);
|
|
|
|
pub type Result<T> = std::result::Result<T, Error>;
|
|
|
|
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),
|
|
}
|
|
}
|
|
}
|
|
|
|
pub fn func1() -> Result<()> {
|
|
func2().map_err(|e| cherr!(e, ErrorKind::Func2))?;
|
|
let filename = String::from("bar.txt");
|
|
do_some_io().map_err(|e| cherr!(e, ErrorKind::IO(filename)))?;
|
|
Ok(())
|
|
}
|
|
}
|
|
|
|
fn main() -> Result<(), Box<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: &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);
|
|
}
|
|
Ok(())
|
|
}
|
|
</code></pre></pre>
|
|
<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="playpen"><code class="language-rust">pub mod mycrate {
|
|
use std::error::Error as StdError;
|
|
|
|
use 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! mcherr {
|
|
( $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(mcherr!(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! mcherr {
|
|
( $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(mcherr!(ErrorKind::Func2))?;
|
|
let filename = String::from("bar.txt");
|
|
do_some_io().map_err(mcherr!(ErrorKind::IO(filename)))?;
|
|
Ok(())
|
|
}
|
|
}
|
|
|
|
fn main() -> Result<(), Box<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: &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);
|
|
}
|
|
Ok(())
|
|
}
|
|
</code></pre></pre>
|
|
<h1><a class="header" href="#the-end" id="the-end">The End</a></h1>
|
|
<p>That's it for now…</p>
|
|
<p>Happy error handling!</p>
|
|
<p>To report issues, submit pull request or for the source code, examples and the book source, visit
|
|
the <a href="https://github.com/haraldh/chainerror">Git Repo</a>.</p>
|
|
|
|
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