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< ol class = "chapter" > < li class = "chapter-item expanded affix " > < a href = "index.html" class = "active" > chainerror< / a > < / li > < li class = "chapter-item expanded " > < a href = "tutorial1.html" > < strong aria-hidden = "true" > 1.< / strong > Simple String Errors< / a > < / li > < li class = "chapter-item expanded " > < a href = "tutorial2.html" > < strong aria-hidden = "true" > 2.< / strong > Simple Chained String Errors< / a > < / li > < li class = "chapter-item expanded " > < a href = "tutorial3.html" > < strong aria-hidden = "true" > 3.< / strong > Mapping Errors< / a > < / li > < li class = "chapter-item expanded " > < a href = "tutorial4.html" > < strong aria-hidden = "true" > 4.< / strong > More Information< / a > < / li > < li class = "chapter-item expanded " > < a href = "tutorial5.html" > < strong aria-hidden = "true" > 5.< / strong > The source() of Errors< / a > < / li > < li class = "chapter-item expanded " > < a href = "tutorial6.html" > < strong aria-hidden = "true" > 6.< / strong > Downcast the Errors< / a > < / li > < li class = "chapter-item expanded " > < a href = "tutorial7.html" > < strong aria-hidden = "true" > 7.< / strong > The root cause of all Errors< / a > < / li > < li class = "chapter-item expanded " > < a href = "tutorial8.html" > < strong aria-hidden = "true" > 8.< / strong > Finding an Error cause< / a > < / li > < li class = "chapter-item expanded " > < a href = "tutorial9.html" > < strong aria-hidden = "true" > 9.< / strong > Selective Error Handling< / a > < / li > < li class = "chapter-item expanded " > < a href = "tutorial10.html" > < strong aria-hidden = "true" > 10.< / strong > ErrorKind to the rescue< / a > < / li > < li class = "chapter-item expanded " > < a href = "tutorial11.html" > < strong aria-hidden = "true" > 11.< / strong > Debug for the ErrorKind< / a > < / li > < li class = "chapter-item expanded " > < a href = "tutorial12.html" > < strong aria-hidden = "true" > 12.< / strong > Deref for the ErrorKind< / a > < / li > < li class = "chapter-item expanded " > < a href = "tutorial13.html" > < strong aria-hidden = "true" > 13.< / strong > Writing a library< / a > < / li > < li class = "chapter-item expanded " > < a href = "tutorial14.html" > < strong aria-hidden = "true" > 14.< / strong > Going back to std< / a > < / li > < li class = "chapter-item expanded affix " > < a href = "end.html" > The End< / a > < / li > < / ol >
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< main >
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< p > < a href = "https://crates.io/crates/chainerror" > < img src = "https://img.shields.io/crates/v/chainerror.svg" alt = "Crate" / > < / a >
< a href = "https://docs.rs/chainerror/" > < img src = "https://img.shields.io/badge/api-rustdoc-blue.svg" alt = "Rust Documentation" / > < / a >
< a href = "https://coveralls.io/github/haraldh/chainerror?branch=master" > < img src = "https://coveralls.io/repos/github/haraldh/chainerror/badge.svg?branch=master" alt = "Coverage Status" / > < / a >
< a href = "https://github.com/haraldh/chainerror/actions?query=workflow%3A%22Rust%22" > < img src = "https://github.com/haraldh/chainerror/workflows/Rust/badge.svg" alt = "Workflow Status" / > < / a >
< a href = "https://isitmaintained.com/project/haraldh/chainerror" title = "Average time to resolve an issue" > < img src = "https://isitmaintained.com/badge/resolution/haraldh/chainerror.svg" alt = "Average time to resolve an issue" / > < / a >
< a href = "https://isitmaintained.com/project/haraldh/chainerror" title = "Percentage of issues still open" > < img src = "https://isitmaintained.com/badge/open/haraldh/chainerror.svg" alt = "Percentage of issues still open" / > < / a >
< img src = "https://img.shields.io/badge/maintenance-activly--developed-brightgreen.svg" alt = "Maintenance" / > < / p >
< h1 > < a class = "header" href = "#chainerror" id = "chainerror" > chainerror< / a > < / h1 >
< p > < code > chainerror< / code > provides an error backtrace without doing a real backtrace, so even after you < code > strip< / code > your
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binaries, you still have the error backtrace.< / p >
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< p > Having nested function returning errors, the output doesn't tell where the error originates from.< / p >
< pre > < pre class = "playground" > < code class = "language-rust" > use std::path::PathBuf;
type BoxedError = Box< dyn std::error::Error + Send + Sync> ;
fn read_config_file(path: PathBuf) -> Result< (), BoxedError> {
// do stuff, return other errors
let _buf = std::fs::read_to_string(& path)?;
// do stuff, return other errors
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Ok(())
}
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fn process_config_file() -> Result< (), BoxedError> {
// do stuff, return other errors
let _buf = read_config_file(" foo.txt" .into())?;
// do stuff, return other errors
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Ok(())
}
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fn main() {
if let Err(e) = process_config_file() {
eprintln!(" Error:\n{:?}" , e);
}
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}
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< / code > < / pre > < / pre >
< p > This gives the output:< / p >
< pre > < code class = "language-console" > Error:
Os { code: 2, kind: NotFound, message: " No such file or directory" }
< / code > < / pre >
< p > and you have no idea where it comes from.< / p >
< p > With < code > chainerror< / code > , you can supply a context and get a nice error backtrace:< / p >
< pre > < pre class = "playground" > < code class = "language-rust" > use chainerror::prelude::v1::*;
use std::path::PathBuf;
type BoxedError = Box< dyn std::error::Error + Send + Sync> ;
fn read_config_file(path: PathBuf) -> Result< (), BoxedError> {
// do stuff, return other errors
let _buf = std::fs::read_to_string(& path).context(format!(" Reading file: {:?}" , & path))?;
// do stuff, return other errors
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Ok(())
}
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fn process_config_file() -> Result< (), BoxedError> {
// do stuff, return other errors
let _buf = read_config_file(" foo.txt" .into()).context(" read the config file" )?;
// do stuff, return other errors
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Ok(())
}
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fn main() {
if let Err(e) = process_config_file() {
eprintln!(" Error:\n{:?}" , e);
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}
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}
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< / code > < / pre > < / pre >
< p > with the output:< / p >
< pre > < code class = "language-console" > Error:
examples/simple.rs:14:51: read the config file
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Caused by:
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examples/simple.rs:7:47: Reading file: " foo.txt"
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Caused by:
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Os { code: 2, kind: NotFound, message: " No such file or directory" }
< / code > < / pre >
< p > < code > chainerror< / code > uses < code > .source()< / code > of < code > std::error::Error< / code > along with < code > #[track_caller]< / code > and < code > Location< / 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 > < code > chainerror< / code > has no dependencies!< / p >
< p > Debug information is worth it!< / p >
< h3 > < a class = "header" href = "#features" id = "features" > Features< / a > < / h3 >
< p > < code > display-cause< / code >
: turn on printing a backtrace of the errors in < code > Display< / code > < / p >
< h2 > < a class = "header" href = "#tutorial" id = "tutorial" > Tutorial< / a > < / h2 >
< p > Read the < a href = "https://haraldh.github.io/chainerror/tutorial1.html" > Tutorial< / a > < / p >
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< h2 > < a class = "header" href = "#license" id = "license" > License< / a > < / h2 >
< p > Licensed under either of< / p >
< ul >
< li > Apache License, Version 2.0, (< a href = "LICENSE-APACHE" > LICENSE-APACHE< / a > or https://www.apache.org/licenses/LICENSE-2.0)< / li >
< li > MIT license (< a href = "LICENSE-MIT" > LICENSE-MIT< / a > or https://opensource.org/licenses/MIT)< / li >
< / ul >
< p > at your option.< / p >
< h3 > < a class = "header" href = "#contribution" id = "contribution" > Contribution< / a > < / h3 >
< p > Unless you explicitly state otherwise, any contribution intentionally
submitted for inclusion in the work by you, as defined in the Apache-2.0
license, shall be dual licensed as above, without any additional terms or
conditions.< / p >
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