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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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< main >
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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;
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use std::result::Result;
fn do_some_io() -> Result< (), Box< Error> > {
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Err(io::Error::from(io::ErrorKind::NotFound))?;
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Ok(())
}
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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" ))?;
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Ok(())
}
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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)
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}
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}
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)))?;
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Ok(())
}
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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);
}
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}
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< / 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 >
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