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< title > The root cause of all Errors - chainerror< / title >
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< ol class = "chapter" > < li class = "chapter-item expanded affix " > < a href = "index.html" > 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" class = "active" > < 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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< 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 >
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< 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
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to call < code > .find_cause::< io::Error> ()< / code > . < / p >
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< 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 >
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< pre > < pre class = "playground" > < code class = "language-rust" > use chainerror::prelude::v1::*;
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use std::error::Error;
use std::io;
use std::result::Result;
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fn do_some_io() -> Result< (), Box< dyn Error + Send + Sync> > {
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Err(io::Error::from(io::ErrorKind::NotFound))?;
Ok(())
}
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fn func2() -> Result< (), Box< dyn Error + Send + Sync> > {
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let filename = " foo.txt" ;
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do_some_io().context(format!(" Error reading '{}'" , filename))?;
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Ok(())
}
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fn func1() -> Result< (), Box< dyn Error + Send + Sync> > {
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func2().context(format!(" func1 error" ))?;
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Ok(())
}
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fn main() -> Result< (), Box< dyn Error + Send + Sync> > {
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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);
}
}
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std::process::exit(1);
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}
Ok(())
}
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< span class = "boring" > #[allow(dead_code)]
< / span > < span class = "boring" > mod chainerror {
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< / span > < span class = "boring" > //! `chainerror` provides an error backtrace without doing a real backtrace, so even after you `strip` your
< / span > < span class = "boring" > //! binaries, you still have the error backtrace.
< / span > < span class = "boring" > //!
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< / span > < span class = "boring" > //! Having nested function returning errors, the output doesn't tell where the error originates from.
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< / span > < span class = "boring" > //!
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< / span > < span class = "boring" > //! ```rust
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< / span > < span class = "boring" > //! use std::path::PathBuf;
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< / span > < span class = "boring" > //!
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< / span > < span class = "boring" > //! type BoxedError = Box< dyn std::error::Error + Send + Sync> ;
< / span > < span class = "boring" > //! fn read_config_file(path: PathBuf) -> Result< (), BoxedError> {
< / span > < span class = "boring" > //! // do stuff, return other errors
< / span > < span class = "boring" > //! let _buf = std::fs::read_to_string(& path)?;
< / span > < span class = "boring" > //! // do stuff, return other errors
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< / span > < span class = "boring" > //! Ok(())
< / span > < span class = "boring" > //! }
< / span > < span class = "boring" > //!
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< / span > < span class = "boring" > //! fn process_config_file() -> Result< (), BoxedError> {
< / span > < span class = "boring" > //! // do stuff, return other errors
< / span > < span class = "boring" > //! let _buf = read_config_file(" foo.txt" .into())?;
< / span > < span class = "boring" > //! // do stuff, return other errors
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< / span > < span class = "boring" > //! Ok(())
< / span > < span class = "boring" > //! }
< / span > < span class = "boring" > //!
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< / span > < span class = "boring" > //! fn main() {
< / span > < span class = "boring" > //! if let Err(e) = process_config_file() {
< / span > < span class = "boring" > //! eprintln!(" Error:\n{:?}" , e);
< / span > < span class = "boring" > //! }
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< / span > < span class = "boring" > //! }
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< / span > < span class = "boring" > //! ```
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< / span > < span class = "boring" > //!
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< / span > < span class = "boring" > //! This gives the output:
< / span > < span class = "boring" > //! ```console
< / span > < span class = "boring" > //! Error:
< / span > < span class = "boring" > //! Os { code: 2, kind: NotFound, message: " No such file or directory" }
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< / span > < span class = "boring" > //! ```
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< / span > < span class = "boring" > //! and you have no idea where it comes from.
< / span > < span class = "boring" > //!
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< / span > < span class = "boring" > //!
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< / span > < span class = "boring" > //! With `chainerror`, you can supply a context and get a nice error backtrace:
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< / span > < span class = "boring" > //!
< / span > < span class = "boring" > //! ```rust
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< / span > < span class = "boring" > //! use chainerror::prelude::v1::*;
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< / span > < span class = "boring" > //! use std::path::PathBuf;
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< / span > < span class = "boring" > //!
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< / span > < span class = "boring" > //! type BoxedError = Box< dyn std::error::Error + Send + Sync> ;
< / span > < span class = "boring" > //! fn read_config_file(path: PathBuf) -> Result< (), BoxedError> {
< / span > < span class = "boring" > //! // do stuff, return other errors
< / span > < span class = "boring" > //! let _buf = std::fs::read_to_string(& path).context(format!(" Reading file: {:?}" , & path))?;
< / span > < span class = "boring" > //! // do stuff, return other errors
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< / span > < span class = "boring" > //! Ok(())
< / span > < span class = "boring" > //! }
< / span > < span class = "boring" > //!
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< / span > < span class = "boring" > //! fn process_config_file() -> Result< (), BoxedError> {
< / span > < span class = "boring" > //! // do stuff, return other errors
< / span > < span class = "boring" > //! let _buf = read_config_file(" foo.txt" .into()).context(" read the config file" )?;
< / span > < span class = "boring" > //! // do stuff, return other errors
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< / span > < span class = "boring" > //! Ok(())
< / span > < span class = "boring" > //! }
< / span > < span class = "boring" > //!
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< / span > < span class = "boring" > //! fn main() {
< / span > < span class = "boring" > //! if let Err(e) = process_config_file() {
< / span > < span class = "boring" > //! eprintln!(" Error:\n{:?}" , e);
< / span > < span class = "boring" > //! # assert_eq!(
< / span > < span class = "boring" > //! # format!(" {:?}\n" , e),
< / span > < span class = "boring" > //! # " \
< / span > < span class = "boring" > //! # src/lib.rs:16:51: read the config file\n\
< / span > < span class = "boring" > //! # Caused by:\n\
< / span > < span class = "boring" > //! # src/lib.rs:9:47: Reading file: \" foo.txt\" \n\
< / span > < span class = "boring" > //! # Caused by:\n\
< / span > < span class = "boring" > //! # Os { code: 2, kind: NotFound, message: \" No such file or directory\" }\n\
< / span > < span class = "boring" > //! # " ,
< / span > < span class = "boring" > //! # );
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< / span > < span class = "boring" > //! }
< / span > < span class = "boring" > //! }
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< / span > < span class = "boring" > //! ```
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< / span > < span class = "boring" > //!
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< / span > < span class = "boring" > //! with the output:
< / span > < span class = "boring" > //! ```console
< / span > < span class = "boring" > //! Error:
< / span > < span class = "boring" > //! examples/simple.rs:14:51: read the config file
< / span > < span class = "boring" > //! Caused by:
< / span > < span class = "boring" > //! examples/simple.rs:7:47: Reading file: " foo.txt"
< / span > < span class = "boring" > //! Caused by:
< / span > < span class = "boring" > //! Os { code: 2, kind: NotFound, message: " No such file or directory" }
< / span > < span class = "boring" > //! ```
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< / span > < span class = "boring" > //!
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< / span > < span class = "boring" > //! `chainerror` uses `.source()` of `std::error::Error` along with `#[track_caller]` and `Location` to provide a nice debug error backtrace.
< / span > < span class = "boring" > //! It encapsulates all types, which have `Display + Debug` and can store the error cause internally.
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< / span > < span class = "boring" > //!
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< / span > < span class = "boring" > //! Along with the `ChainError< T> ` struct, `chainerror` comes with some useful helper macros to save a lot of typing.
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< / span > < span class = "boring" > //!
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< / span > < span class = "boring" > //! `chainerror` has no dependencies!
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< / span > < span class = "boring" > //!
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< / span > < span class = "boring" > //! Debug information is worth it!
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< / span > < span class = "boring" > //!
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< / span > < span class = "boring" > //! ## Features
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< / span > < span class = "boring" > //!
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< / span > < span class = "boring" > //! `display-cause`
< / span > < span class = "boring" > //! : turn on printing a backtrace of the errors in `Display`
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< / span > < span class = "boring" > //!
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< / span > < span class = "boring" > //! # Tutorial
< / span > < span class = "boring" > //!
< / span > < span class = "boring" > //! Read the [Tutorial](https://haraldh.github.io/chainerror/tutorial1.html)
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< / span > < span class = "boring" >
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< / span > < span class = "boring" > #![deny(clippy::all)]
< / span > < span class = "boring" > #![deny(clippy::integer_arithmetic)]
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< / span > < span class = "boring" > #![allow(clippy::needless_doctest_main)]
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< / span > < span class = "boring" > #![deny(missing_docs)]
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< / span > < span class = "boring" >
< / span > < span class = "boring" > use std::any::TypeId;
< / span > < span class = "boring" > use std::error::Error;
< / span > < span class = "boring" > use std::fmt::{Debug, Display, Formatter, Result};
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< / span > < span class = "boring" > use std::panic::Location;
< / span > < span class = "boring" >
< / span > < span class = "boring" > pub mod prelude {
< / span > < span class = "boring" > //! convenience prelude
< / span > < span class = "boring" > pub mod v1 {
< / span > < span class = "boring" > //! convenience prelude
< / span > < span class = "boring" > pub use super::super::ChainErrorDown as _;
< / span > < span class = "boring" > pub use super::super::ResultTrait as _;
< / span > < span class = "boring" > pub use super::super::{ChainError, ChainResult};
< / span > < span class = "boring" > pub use crate::{derive_err_kind, derive_str_context};
< / span > < span class = "boring" > }
< / span > < span class = "boring" > }
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< / span > < span class = "boring" >
< / span > < span class = "boring" > /// chains an inner error kind `T` with a causing error
< / span > < span class = "boring" > pub struct ChainError< T> {
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< / span > < span class = "boring" > occurrence: Option< String> ,
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< / span > < span class = "boring" > kind: T,
< / span > < span class = "boring" > error_cause: Option< Box< dyn Error + 'static + Send + Sync> > ,
< / span > < span class = "boring" > }
< / span > < span class = "boring" >
< / span > < span class = "boring" > /// convenience type alias
< / span > < span class = "boring" > pub type ChainResult< O, E> = std::result::Result< O, ChainError< E> > ;
< / span > < span class = "boring" >
< / span > < span class = "boring" > impl< T: 'static + Display + Debug> ChainError< T> {
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< / span > < span class = "boring" > /// Use the `context()` or `map_context()` Result methods instead of calling this directly
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< / span > < span class = "boring" > #[inline]
< / span > < span class = "boring" > pub fn new(
< / span > < span class = "boring" > kind: T,
< / span > < span class = "boring" > error_cause: Option< Box< dyn Error + 'static + Send + Sync> > ,
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< / span > < span class = "boring" > occurrence: Option< String> ,
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< / span > < span class = "boring" > ) -> Self {
< / span > < span class = "boring" > Self {
< / span > < span class = "boring" > occurrence,
< / span > < span class = "boring" > kind,
< / span > < span class = "boring" > error_cause,
< / span > < span class = "boring" > }
< / span > < span class = "boring" > }
< / span > < span class = "boring" >
< / span > < span class = "boring" > /// return the root cause of the error chain, if any exists
< / span > < span class = "boring" > pub fn root_cause(& self) -> Option< & (dyn Error + 'static)> {
< / span > < span class = "boring" > self.iter().last()
< / span > < span class = "boring" > }
< / span > < span class = "boring" >
< / span > < span class = "boring" > /// Find the first error cause of type U, if any exists
< / span > < span class = "boring" > ///
< / span > < span class = "boring" > /// # Examples
< / span > < span class = "boring" > ///
< / span > < span class = "boring" > /// ```rust
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< / span > < span class = "boring" > /// use chainerror::prelude::v1::*;
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< / span > < span class = "boring" > /// use std::error::Error;
< / span > < span class = "boring" > /// use std::io;
< / span > < span class = "boring" > ///
< / span > < span class = "boring" > /// fn do_some_io() -> Result< (), Box< dyn Error + Send + Sync> > {
< / span > < span class = "boring" > /// Err(io::Error::from(io::ErrorKind::NotFound))?;
< / span > < span class = "boring" > /// Ok(())
< / span > < span class = "boring" > /// }
< / span > < span class = "boring" > ///
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< / span > < span class = "boring" > /// derive_str_context!(Func2Error);
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< / span > < span class = "boring" > ///
< / span > < span class = "boring" > /// fn func2() -> Result< (), Box< dyn Error + Send + Sync> > {
< / span > < span class = "boring" > /// let filename = " foo.txt" ;
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< / span > < span class = "boring" > /// do_some_io().context(Func2Error(format!(" Error reading '{}'" , filename)))?;
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< / span > < span class = "boring" > /// Ok(())
< / span > < span class = "boring" > /// }
< / span > < span class = "boring" > ///
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< / span > < span class = "boring" > /// derive_str_context!(Func1Error);
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< / span > < span class = "boring" > ///
< / span > < span class = "boring" > /// fn func1() -> Result< (), Box< dyn Error + Send + Sync> > {
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< / span > < span class = "boring" > /// func2().context(Func1Error(" func1 error" .into()))?;
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< / span > < span class = "boring" > /// Ok(())
< / span > < span class = "boring" > /// }
< / span > < span class = "boring" > ///
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< / span > < span class = "boring" > /// if let Err(e) = func1() {
< / span > < span class = "boring" > /// if let Some(f1err) = e.downcast_chain_ref::< Func1Error> () {
< / span > < span class = "boring" > /// assert!(f1err.find_cause::< io::Error> ().is_some());
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< / span > < span class = "boring" > ///
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< / span > < span class = "boring" > /// assert!(f1err.find_chain_cause::< Func2Error> ().is_some());
< / span > < span class = "boring" > /// }
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< / span > < span class = "boring" > /// # else {
< / span > < span class = "boring" > /// # panic!();
< / span > < span class = "boring" > /// # }
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< / span > < span class = "boring" > /// }
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< / span > < span class = "boring" > /// # else {
< / span > < span class = "boring" > /// # unreachable!();
< / span > < span class = "boring" > /// # }
< / span > < span class = "boring" > /// ```
< / span > < span class = "boring" > #[inline]
< / span > < span class = "boring" > pub fn find_cause< U: Error + 'static> (& self) -> Option< & U> {
< / span > < span class = "boring" > self.iter().filter_map(Error::downcast_ref::< U> ).next()
< / span > < span class = "boring" > }
< / span > < span class = "boring" >
< / span > < span class = "boring" > /// Find the first error cause of type `ChainError< U> `, if any exists
< / span > < span class = "boring" > ///
< / span > < span class = "boring" > /// Same as `find_cause`, but hides the `ChainError< U> ` implementation internals
< / span > < span class = "boring" > ///
< / span > < span class = "boring" > /// # Examples
< / span > < span class = "boring" > ///
< / span > < span class = "boring" > /// ```rust
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< / span > < span class = "boring" > /// # use chainerror::prelude::v1::*;
< / span > < span class = "boring" > /// # derive_str_context!(FooError);
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< / span > < span class = "boring" > /// # let err = ChainError::new(String::new(), None, None);
< / span > < span class = "boring" > /// // Instead of writing
< / span > < span class = "boring" > /// err.find_cause::< ChainError< FooError> > ();
< / span > < span class = "boring" > ///
< / span > < span class = "boring" > /// // leave out the ChainError< FooError> implementation detail
< / span > < span class = "boring" > /// err.find_chain_cause::< FooError> ();
< / span > < span class = "boring" > /// ```
< / span > < span class = "boring" > #[inline]
< / span > < span class = "boring" > pub fn find_chain_cause< U: Error + 'static> (& self) -> Option< & ChainError< U> > {
< / span > < span class = "boring" > self.iter()
< / span > < span class = "boring" > .filter_map(Error::downcast_ref::< ChainError< U> > )
< / span > < span class = "boring" > .next()
< / span > < span class = "boring" > }
< / span > < span class = "boring" >
< / span > < span class = "boring" > /// Find the first error cause of type `ChainError< U> ` or `U`, if any exists and return `U`
< / span > < span class = "boring" > ///
< / span > < span class = "boring" > /// Same as `find_cause` and `find_chain_cause`, but hides the `ChainError< U> ` implementation internals
< / span > < span class = "boring" > ///
< / span > < span class = "boring" > /// # Examples
< / span > < span class = "boring" > ///
< / span > < span class = "boring" > /// ```rust
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< / span > < span class = "boring" > /// # use chainerror::prelude::v1::*;
< / span > < span class = "boring" > /// # derive_str_context!(FooErrorKind);
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< / span > < span class = "boring" > /// # let err = ChainError::new(String::new(), None, None);
< / span > < span class = "boring" > /// // Instead of writing
< / span > < span class = "boring" > /// err.find_cause::< ChainError< FooErrorKind> > ();
< / span > < span class = "boring" > /// // and/or
< / span > < span class = "boring" > /// err.find_chain_cause::< FooErrorKind> ();
< / span > < span class = "boring" > /// // and/or
< / span > < span class = "boring" > /// err.find_cause::< FooErrorKind> ();
< / span > < span class = "boring" > ///
< / span > < span class = "boring" > /// // leave out the ChainError< FooErrorKind> implementation detail
< / span > < span class = "boring" > /// err.find_kind_or_cause::< FooErrorKind> ();
< / span > < span class = "boring" > /// ```
< / span > < span class = "boring" > #[inline]
< / span > < span class = "boring" > pub fn find_kind_or_cause< U: Error + 'static> (& self) -> Option< & U> {
< / span > < span class = "boring" > self.iter()
< / span > < span class = "boring" > .filter_map(|e| {
< / span > < span class = "boring" > e.downcast_ref::< ChainError< U> > ()
< / span > < span class = "boring" > .map(|e| e.kind())
< / span > < span class = "boring" > .or_else(|| e.downcast_ref::< U> ())
< / span > < span class = "boring" > })
< / span > < span class = "boring" > .next()
< / span > < span class = "boring" > }
< / span > < span class = "boring" >
< / span > < span class = "boring" > /// Return a reference to T of `ChainError< T> `
< / span > < span class = "boring" > ///
< / span > < span class = "boring" > /// # Examples
< / span > < span class = "boring" > ///
< / span > < span class = "boring" > /// ```rust
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< / span > < span class = "boring" > /// use chainerror::prelude::v1::*;
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< / span > < span class = "boring" > /// use std::error::Error;
< / span > < span class = "boring" > /// use std::io;
< / span > < span class = "boring" > ///
< / span > < span class = "boring" > /// fn do_some_io() -> Result< (), Box< dyn Error + Send + Sync> > {
< / span > < span class = "boring" > /// Err(io::Error::from(io::ErrorKind::NotFound))?;
< / span > < span class = "boring" > /// Ok(())
< / span > < span class = "boring" > /// }
< / span > < span class = "boring" > ///
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< / span > < span class = "boring" > /// derive_str_context!(Func2Error);
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< / span > < span class = "boring" > ///
< / span > < span class = "boring" > /// fn func2() -> Result< (), Box< dyn Error + Send + Sync> > {
< / span > < span class = "boring" > /// let filename = " foo.txt" ;
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< / span > < span class = "boring" > /// do_some_io().context(Func2Error(format!(" Error reading '{}'" , filename)))?;
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< / span > < span class = "boring" > /// Ok(())
< / span > < span class = "boring" > /// }
< / span > < span class = "boring" > ///
< / span > < span class = "boring" > /// #[derive(Debug)]
< / span > < span class = "boring" > /// enum Func1ErrorKind {
< / span > < span class = "boring" > /// Func2,
< / span > < span class = "boring" > /// IO(String),
< / span > < span class = "boring" > /// }
< / span > < span class = "boring" > ///
< / span > < span class = "boring" > /// /// impl ::std::fmt::Display for Func1ErrorKind {…}
< / span > < span class = "boring" > /// # impl ::std::fmt::Display for Func1ErrorKind {
< / span > < span class = "boring" > /// # fn fmt(& self, f: & mut ::std::fmt::Formatter) -> ::std::fmt::Result {
< / span > < span class = "boring" > /// # match self {
< / span > < span class = "boring" > /// # Func1ErrorKind::Func2 => write!(f, " func1 error calling func2" ),
< / span > < span class = "boring" > /// # Func1ErrorKind::IO(filename) => write!(f, " Error reading '{}'" , filename),
< / span > < span class = "boring" > /// # }
< / span > < span class = "boring" > /// # }
< / span > < span class = "boring" > /// # }
< / span > < span class = "boring" > ///
< / span > < span class = "boring" > /// fn func1() -> ChainResult< (), Func1ErrorKind> {
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< / span > < span class = "boring" > /// func2().context(Func1ErrorKind::Func2)?;
< / span > < span class = "boring" > /// do_some_io().context(Func1ErrorKind::IO(" bar.txt" .into()))?;
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< / span > < span class = "boring" > /// Ok(())
< / span > < span class = "boring" > /// }
< / span > < span class = "boring" > ///
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< / span > < span class = "boring" > /// if let Err(e) = func1() {
< / span > < span class = "boring" > /// match e.kind() {
< / span > < span class = "boring" > /// Func1ErrorKind::Func2 => {}
< / span > < span class = "boring" > /// Func1ErrorKind::IO(filename) => panic!(),
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< / span > < span class = "boring" > /// }
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< / span > < span class = "boring" > /// }
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< / span > < span class = "boring" > /// # else {
< / span > < span class = "boring" > /// # unreachable!();
< / span > < span class = "boring" > /// # }
< / span > < span class = "boring" > /// ```
< / span > < span class = "boring" > #[inline]
< / span > < span class = "boring" > pub fn kind(& self) -> & T {
< / span > < span class = "boring" > & self.kind
< / span > < span class = "boring" > }
< / span > < span class = "boring" >
< / span > < span class = "boring" > /// Returns an Iterator over all error causes/sources
< / span > < span class = "boring" > ///
< / span > < span class = "boring" > /// # Example
< / span > < span class = "boring" > #[inline]
< / span > < span class = "boring" > pub fn iter(& self) -> impl Iterator< Item = & (dyn Error + 'static)> {
< / span > < span class = "boring" > ErrorIter {
< / span > < span class = "boring" > current: Some(self),
< / span > < span class = "boring" > }
< / span > < span class = "boring" > }
< / span > < span class = "boring" > }
< / span > < span class = "boring" >
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< / span > < span class = "boring" > /// Convenience methods for `Result< > ` to turn the error into a decorated ChainError
< / span > < span class = "boring" > pub trait ResultTrait< O, E: Into< Box< dyn Error + 'static + Send + Sync> > > {
< / span > < span class = "boring" > /// Decorate the error with a `kind` of type `T` and the source `Location`
< / span > < span class = "boring" > fn context< T: 'static + Display + Debug> (
< / span > < span class = "boring" > self,
< / span > < span class = "boring" > kind: T,
< / span > < span class = "boring" > ) -> std::result::Result< O, ChainError< T> > ;
< / span > < span class = "boring" >
< / span > < span class = "boring" > /// Decorate the `error` with a `kind` of type `T` produced with a `FnOnce(& error)` and the source `Location`
< / span > < span class = "boring" > fn map_context< T: 'static + Display + Debug, F: FnOnce(& E) -> T> (
< / span > < span class = "boring" > self,
< / span > < span class = "boring" > op: F,
< / span > < span class = "boring" > ) -> std::result::Result< O, ChainError< T> > ;
< / span > < span class = "boring" > }
< / span > < span class = "boring" >
< / span > < span class = "boring" > impl< O, E: Into< Box< dyn Error + 'static + Send + Sync> > > ResultTrait< O, E>
< / span > < span class = "boring" > for std::result::Result< O, E>
< / span > < span class = "boring" > {
< / span > < span class = "boring" > #[track_caller]
< / span > < span class = "boring" > fn context< T: 'static + Display + Debug> (
< / span > < span class = "boring" > self,
< / span > < span class = "boring" > kind: T,
< / span > < span class = "boring" > ) -> std::result::Result< O, ChainError< T> > {
< / span > < span class = "boring" > match self {
< / span > < span class = "boring" > Ok(t) => Ok(t),
< / span > < span class = "boring" > Err(error_cause) => Err(ChainError::new(
< / span > < span class = "boring" > kind,
< / span > < span class = "boring" > Some(error_cause.into()),
< / span > < span class = "boring" > Some(Location::caller().to_string()),
< / span > < span class = "boring" > )),
< / span > < span class = "boring" > }
< / span > < span class = "boring" > }
< / span > < span class = "boring" >
< / span > < span class = "boring" > #[track_caller]
< / span > < span class = "boring" > fn map_context< T: 'static + Display + Debug, F: FnOnce(& E) -> T> (
< / span > < span class = "boring" > self,
< / span > < span class = "boring" > op: F,
< / span > < span class = "boring" > ) -> std::result::Result< O, ChainError< T> > {
< / span > < span class = "boring" > match self {
< / span > < span class = "boring" > Ok(t) => Ok(t),
< / span > < span class = "boring" > Err(error_cause) => {
< / span > < span class = "boring" > let kind = op(& error_cause);
< / span > < span class = "boring" > Err(ChainError::new(
< / span > < span class = "boring" > kind,
< / span > < span class = "boring" > Some(error_cause.into()),
< / span > < span class = "boring" > Some(Location::caller().to_string()),
< / span > < span class = "boring" > ))
< / span > < span class = "boring" > }
< / span > < span class = "boring" > }
< / span > < span class = "boring" > }
< / span > < span class = "boring" > }
< / span > < span class = "boring" >
< / span > < span class = "boring" > /// An iterator over all error causes/sources
< / span > < span class = "boring" > pub struct ErrorIter< 'a> {
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< / span > < span class = "boring" > current: Option< & 'a (dyn Error + 'static)> ,
< / span > < span class = "boring" > }
< / span > < span class = "boring" >
< / span > < span class = "boring" > impl< 'a> Iterator for ErrorIter< 'a> {
< / span > < span class = "boring" > type Item = & 'a (dyn Error + 'static);
< / span > < span class = "boring" >
< / span > < span class = "boring" > #[inline]
< / span > < span class = "boring" > fn next(& mut self) -> Option< Self::Item> {
< / span > < span class = "boring" > let current = self.current;
< / span > < span class = "boring" > self.current = self.current.and_then(Error::source);
< / span > < span class = "boring" > current
< / span > < span class = "boring" > }
< / span > < span class = "boring" > }
< / span > < span class = "boring" >
< / span > < span class = "boring" > impl< T: 'static + Display + Debug> std::ops::Deref for ChainError< T> {
< / span > < span class = "boring" > type Target = T;
< / span > < span class = "boring" >
< / span > < span class = "boring" > #[inline]
< / span > < span class = "boring" > fn deref(& self) -> & Self::Target {
< / span > < span class = "boring" > & self.kind
< / span > < span class = "boring" > }
< / span > < span class = "boring" > }
< / span > < span class = "boring" >
< / span > < span class = "boring" > /// Convenience trait to hide the `ChainError< T> ` implementation internals
< / span > < span class = "boring" > pub trait ChainErrorDown {
< / span > < span class = "boring" > /// Test if of type `ChainError< T> `
< / span > < span class = "boring" > fn is_chain< T: 'static + Display + Debug> (& self) -> bool;
< / span > < span class = "boring" > /// Downcast to a reference of `ChainError< T> `
< / span > < span class = "boring" > fn downcast_chain_ref< T: 'static + Display + Debug> (& self) -> Option< & ChainError< T> > ;
< / span > < span class = "boring" > /// Downcast to a mutable reference of `ChainError< T> `
< / span > < span class = "boring" > fn downcast_chain_mut< T: 'static + Display + Debug> (& mut self) -> Option< & mut ChainError< T> > ;
< / span > < span class = "boring" > /// Downcast to T of `ChainError< T> `
< / span > < span class = "boring" > fn downcast_inner_ref< T: 'static + Error> (& self) -> Option< & T> ;
< / span > < span class = "boring" > /// Downcast to T mutable reference of `ChainError< T> `
< / span > < span class = "boring" > fn downcast_inner_mut< T: 'static + Error> (& mut self) -> Option< & mut T> ;
< / span > < span class = "boring" > }
< / span > < span class = "boring" >
< / span > < span class = "boring" > impl< U: 'static + Display + Debug> ChainErrorDown for ChainError< U> {
< / span > < span class = "boring" > #[inline]
< / span > < span class = "boring" > fn is_chain< T: 'static + Display + Debug> (& self) -> bool {
< / span > < span class = "boring" > TypeId::of::< T> () == TypeId::of::< U> ()
< / span > < span class = "boring" > }
< / span > < span class = "boring" >
< / span > < span class = "boring" > #[inline]
< / span > < span class = "boring" > fn downcast_chain_ref< T: 'static + Display + Debug> (& self) -> Option< & ChainError< T> > {
< / span > < span class = "boring" > if self.is_chain::< T> () {
< / span > < span class = "boring" > #[allow(clippy::cast_ptr_alignment)]
< / span > < span class = "boring" > unsafe {
< / span > < span class = "boring" > #[allow(trivial_casts)]
< / span > < span class = "boring" > Some(& *(self as *const dyn Error as *const & ChainError< T> ))
< / span > < span class = "boring" > }
< / span > < span class = "boring" > } else {
< / span > < span class = "boring" > None
< / span > < span class = "boring" > }
< / span > < span class = "boring" > }
< / span > < span class = "boring" >
< / span > < span class = "boring" > #[inline]
< / span > < span class = "boring" > fn downcast_chain_mut< T: 'static + Display + Debug> (& mut self) -> Option< & mut ChainError< T> > {
< / span > < span class = "boring" > if self.is_chain::< T> () {
< / span > < span class = "boring" > #[allow(clippy::cast_ptr_alignment)]
< / span > < span class = "boring" > unsafe {
< / span > < span class = "boring" > #[allow(trivial_casts)]
< / span > < span class = "boring" > Some(& mut *(self as *mut dyn Error as *mut & mut ChainError< T> ))
< / span > < span class = "boring" > }
< / span > < span class = "boring" > } else {
< / span > < span class = "boring" > None
< / span > < span class = "boring" > }
< / span > < span class = "boring" > }
< / span > < span class = "boring" > #[inline]
< / span > < span class = "boring" > fn downcast_inner_ref< T: 'static + Error> (& self) -> Option< & T> {
< / span > < span class = "boring" > if self.is_chain::< T> () {
< / span > < span class = "boring" > #[allow(clippy::cast_ptr_alignment)]
< / span > < span class = "boring" > unsafe {
< / span > < span class = "boring" > #[allow(trivial_casts)]
< / span > < span class = "boring" > Some(& (*(self as *const dyn Error as *const & ChainError< T> )).kind)
< / span > < span class = "boring" > }
< / span > < span class = "boring" > } else {
< / span > < span class = "boring" > None
< / span > < span class = "boring" > }
< / span > < span class = "boring" > }
< / span > < span class = "boring" >
< / span > < span class = "boring" > #[inline]
< / span > < span class = "boring" > fn downcast_inner_mut< T: 'static + Error> (& mut self) -> Option< & mut T> {
< / span > < span class = "boring" > if self.is_chain::< T> () {
< / span > < span class = "boring" > #[allow(clippy::cast_ptr_alignment)]
< / span > < span class = "boring" > unsafe {
< / span > < span class = "boring" > #[allow(trivial_casts)]
< / span > < span class = "boring" > Some(& mut (*(self as *mut dyn Error as *mut & mut ChainError< T> )).kind)
< / span > < span class = "boring" > }
< / span > < span class = "boring" > } else {
< / span > < span class = "boring" > None
< / span > < span class = "boring" > }
< / span > < span class = "boring" > }
< / span > < span class = "boring" > }
< / span > < span class = "boring" >
< / span > < span class = "boring" > impl ChainErrorDown for dyn Error + 'static {
< / span > < span class = "boring" > #[inline]
< / span > < span class = "boring" > fn is_chain< T: 'static + Display + Debug> (& self) -> bool {
< / span > < span class = "boring" > self.is::< ChainError< T> > ()
< / span > < span class = "boring" > }
< / span > < span class = "boring" >
< / span > < span class = "boring" > #[inline]
< / span > < span class = "boring" > fn downcast_chain_ref< T: 'static + Display + Debug> (& self) -> Option< & ChainError< T> > {
< / span > < span class = "boring" > self.downcast_ref::< ChainError< T> > ()
< / span > < span class = "boring" > }
< / span > < span class = "boring" >
< / span > < span class = "boring" > #[inline]
< / span > < span class = "boring" > fn downcast_chain_mut< T: 'static + Display + Debug> (& mut self) -> Option< & mut ChainError< T> > {
< / span > < span class = "boring" > self.downcast_mut::< ChainError< T> > ()
< / span > < span class = "boring" > }
< / span > < span class = "boring" >
< / span > < span class = "boring" > #[inline]
< / span > < span class = "boring" > fn downcast_inner_ref< T: 'static + Error> (& self) -> Option< & T> {
< / span > < span class = "boring" > self.downcast_ref::< T> ()
< / span > < span class = "boring" > .or_else(|| self.downcast_ref::< ChainError< T> > ().map(|e| e.kind()))
< / span > < span class = "boring" > }
< / span > < span class = "boring" >
< / span > < span class = "boring" > #[inline]
< / span > < span class = "boring" > fn downcast_inner_mut< T: 'static + Error> (& mut self) -> Option< & mut T> {
< / span > < span class = "boring" > if self.is::< T> () {
< / span > < span class = "boring" > return self.downcast_mut::< T> ();
< / span > < span class = "boring" > }
< / span > < span class = "boring" >
< / span > < span class = "boring" > self.downcast_mut::< ChainError< T> > ()
< / span > < span class = "boring" > .and_then(|e| e.downcast_inner_mut::< T> ())
< / span > < span class = "boring" > }
< / span > < span class = "boring" > }
< / span > < span class = "boring" >
< / span > < span class = "boring" > impl ChainErrorDown for dyn Error + 'static + Send {
< / span > < span class = "boring" > #[inline]
< / span > < span class = "boring" > fn is_chain< T: 'static + Display + Debug> (& self) -> bool {
< / span > < span class = "boring" > self.is::< ChainError< T> > ()
< / span > < span class = "boring" > }
< / span > < span class = "boring" >
< / span > < span class = "boring" > #[inline]
< / span > < span class = "boring" > fn downcast_chain_ref< T: 'static + Display + Debug> (& self) -> Option< & ChainError< T> > {
< / span > < span class = "boring" > self.downcast_ref::< ChainError< T> > ()
< / span > < span class = "boring" > }
< / span > < span class = "boring" >
< / span > < span class = "boring" > #[inline]
< / span > < span class = "boring" > fn downcast_chain_mut< T: 'static + Display + Debug> (& mut self) -> Option< & mut ChainError< T> > {
< / span > < span class = "boring" > self.downcast_mut::< ChainError< T> > ()
< / span > < span class = "boring" > }
< / span > < span class = "boring" >
< / span > < span class = "boring" > #[inline]
< / span > < span class = "boring" > fn downcast_inner_ref< T: 'static + Error> (& self) -> Option< & T> {
< / span > < span class = "boring" > self.downcast_ref::< T> ()
< / span > < span class = "boring" > .or_else(|| self.downcast_ref::< ChainError< T> > ().map(|e| e.kind()))
< / span > < span class = "boring" > }
< / span > < span class = "boring" >
< / span > < span class = "boring" > #[inline]
< / span > < span class = "boring" > fn downcast_inner_mut< T: 'static + Error> (& mut self) -> Option< & mut T> {
< / span > < span class = "boring" > if self.is::< T> () {
< / span > < span class = "boring" > return self.downcast_mut::< T> ();
< / span > < span class = "boring" > }
< / span > < span class = "boring" >
< / span > < span class = "boring" > self.downcast_mut::< ChainError< T> > ()
< / span > < span class = "boring" > .and_then(|e| e.downcast_inner_mut::< T> ())
< / span > < span class = "boring" > }
< / span > < span class = "boring" > }
< / span > < span class = "boring" >
< / span > < span class = "boring" > impl ChainErrorDown for dyn Error + 'static + Send + Sync {
< / span > < span class = "boring" > #[inline]
< / span > < span class = "boring" > fn is_chain< T: 'static + Display + Debug> (& self) -> bool {
< / span > < span class = "boring" > self.is::< ChainError< T> > ()
< / span > < span class = "boring" > }
< / span > < span class = "boring" >
< / span > < span class = "boring" > #[inline]
< / span > < span class = "boring" > fn downcast_chain_ref< T: 'static + Display + Debug> (& self) -> Option< & ChainError< T> > {
< / span > < span class = "boring" > self.downcast_ref::< ChainError< T> > ()
< / span > < span class = "boring" > }
< / span > < span class = "boring" >
< / span > < span class = "boring" > #[inline]
< / span > < span class = "boring" > fn downcast_chain_mut< T: 'static + Display + Debug> (& mut self) -> Option< & mut ChainError< T> > {
< / span > < span class = "boring" > self.downcast_mut::< ChainError< T> > ()
< / span > < span class = "boring" > }
< / span > < span class = "boring" >
< / span > < span class = "boring" > #[inline]
< / span > < span class = "boring" > fn downcast_inner_ref< T: 'static + Error> (& self) -> Option< & T> {
< / span > < span class = "boring" > self.downcast_ref::< T> ()
< / span > < span class = "boring" > .or_else(|| self.downcast_ref::< ChainError< T> > ().map(|e| e.kind()))
< / span > < span class = "boring" > }
< / span > < span class = "boring" >
< / span > < span class = "boring" > #[inline]
< / span > < span class = "boring" > fn downcast_inner_mut< T: 'static + Error> (& mut self) -> Option< & mut T> {
< / span > < span class = "boring" > if self.is::< T> () {
< / span > < span class = "boring" > return self.downcast_mut::< T> ();
< / span > < span class = "boring" > }
< / span > < span class = "boring" >
< / span > < span class = "boring" > self.downcast_mut::< ChainError< T> > ()
< / span > < span class = "boring" > .and_then(|e| e.downcast_inner_mut::< T> ())
< / span > < span class = "boring" > }
< / span > < span class = "boring" > }
< / span > < span class = "boring" >
< / span > < span class = "boring" > impl< T: 'static + Display + Debug> Error for ChainError< T> {
< / span > < span class = "boring" > #[inline]
< / span > < span class = "boring" > fn source(& self) -> Option< & (dyn Error + 'static)> {
< / span > < span class = "boring" > self.error_cause
< / span > < span class = "boring" > .as_ref()
< / span > < span class = "boring" > .map(|e| e.as_ref() as & (dyn Error + 'static))
< / span > < span class = "boring" > }
< / span > < span class = "boring" > }
< / span > < span class = "boring" >
< / span > < span class = "boring" > impl< T: 'static + Display + Debug> Error for & ChainError< T> {
< / span > < span class = "boring" > #[inline]
< / span > < span class = "boring" > fn source(& self) -> Option< & (dyn Error + 'static)> {
< / span > < span class = "boring" > self.error_cause
< / span > < span class = "boring" > .as_ref()
< / span > < span class = "boring" > .map(|e| e.as_ref() as & (dyn Error + 'static))
< / span > < span class = "boring" > }
< / span > < span class = "boring" > }
< / span > < span class = "boring" >
< / span > < span class = "boring" > impl< T: 'static + Display + Debug> Error for & mut ChainError< T> {
< / span > < span class = "boring" > #[inline]
< / span > < span class = "boring" > fn source(& self) -> Option< & (dyn Error + 'static)> {
< / span > < span class = "boring" > self.error_cause
< / span > < span class = "boring" > .as_ref()
< / span > < span class = "boring" > .map(|e| e.as_ref() as & (dyn Error + 'static))
< / span > < span class = "boring" > }
< / span > < span class = "boring" > }
< / span > < span class = "boring" >
< / span > < span class = "boring" > impl< T: 'static + Display + Debug> Display for ChainError< T> {
< / span > < span class = "boring" > #[inline]
< / span > < span class = "boring" > fn fmt(& self, f: & mut Formatter< '_> ) -> Result {
< / span > < span class = "boring" > write!(f, " {}" , self.kind)?;
< / span > < span class = "boring" >
< / span > < span class = "boring" > #[cfg(feature = " display-cause" )]
< / span > < span class = "boring" > {
< / span > < span class = "boring" > if let Some(e) = self.source() {
< / span > < span class = "boring" > writeln!(f, " \nCaused by:" )?;
< / span > < span class = "boring" > Display::fmt(& e, f)?;
< / span > < span class = "boring" > }
< / span > < span class = "boring" > }
< / span > < span class = "boring" > Ok(())
< / span > < span class = "boring" > }
< / span > < span class = "boring" > }
< / span > < span class = "boring" >
< / span > < span class = "boring" > impl< T: 'static + Display + Debug> Debug for ChainError< T> {
< / span > < span class = "boring" > #[inline]
< / span > < span class = "boring" > fn fmt(& self, f: & mut Formatter< '_> ) -> Result {
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< / span > < span class = "boring" > if f.alternate() {
< / span > < span class = "boring" > let mut f = f.debug_struct(& format!(" ChainError< {}> " , std::any::type_name::< T> ()));
< / span > < span class = "boring" >
< / span > < span class = "boring" > let f = f
< / span > < span class = "boring" > .field(" occurrence" , & self.occurrence)
< / span > < span class = "boring" > .field(" kind" , & self.kind)
< / span > < span class = "boring" > .field(" source" , & self.source());
< / span > < span class = "boring" >
< / span > < span class = "boring" > f.finish()
< / span > < span class = "boring" > } else {
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< / span > < span class = "boring" > if let Some(ref o) = self.occurrence {
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< / span > < span class = "boring" > write!(f, " {}: " , o)?;
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< / span > < span class = "boring" > }
< / span > < span class = "boring" >
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< / span > < span class = "boring" > if TypeId::of::< String> () == TypeId::of::< T> ()
< / span > < span class = "boring" > || TypeId::of::< & str> () == TypeId::of::< T> ()
< / span > < span class = "boring" > {
< / span > < span class = "boring" > Display::fmt(& self.kind, f)?;
< / span > < span class = "boring" > } else {
< / span > < span class = "boring" > Debug::fmt(& self.kind, f)?;
< / span > < span class = "boring" > }
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< / span > < span class = "boring" >
< / span > < span class = "boring" > if let Some(e) = self.source() {
< / span > < span class = "boring" > writeln!(f, " \nCaused by:" )?;
< / span > < span class = "boring" > Debug::fmt(& e, f)?;
< / span > < span class = "boring" > }
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< / span > < span class = "boring" > Ok(())
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< / span > < span class = "boring" > }
< / span > < span class = "boring" > }
< / span > < span class = "boring" > }
< / span > < span class = "boring" >
< / span > < span class = "boring" > /// `ChainErrorFrom< T> ` is similar to `From< T> `
< / span > < span class = "boring" > pub trait ChainErrorFrom< T> : Sized {
< / span > < span class = "boring" > /// similar to From< T> ::from()
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< / span > < span class = "boring" > fn chain_error_from(from: T, line_filename: Option< String> ) -> ChainError< Self> ;
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< / span > < span class = "boring" > }
< / span > < span class = "boring" >
< / span > < span class = "boring" > /// `IntoChainError< T> ` is similar to `Into< T> `
< / span > < span class = "boring" > pub trait IntoChainError< T> : Sized {
< / span > < span class = "boring" > /// similar to Into< T> ::into()
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< / span > < span class = "boring" > fn into_chain_error(self, line_filename: Option< String> ) -> ChainError< T> ;
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< / span > < span class = "boring" > }
< / span > < span class = "boring" >
< / span > < span class = "boring" > impl< T, U> IntoChainError< U> for T
< / span > < span class = "boring" > where
< / span > < span class = "boring" > U: ChainErrorFrom< T> ,
< / span > < span class = "boring" > {
< / span > < span class = "boring" > #[inline]
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< / span > < span class = "boring" > fn into_chain_error(self, line_filename: Option< String> ) -> ChainError< U> {
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< / span > < span class = "boring" > U::chain_error_from(self, line_filename)
< / span > < span class = "boring" > }
< / span > < span class = "boring" > }
< / span > < span class = "boring" >
< / span > < span class = "boring" > impl< T, U> ChainErrorFrom< T> for U
< / span > < span class = "boring" > where
< / span > < span class = "boring" > T: Into< U> ,
< / span > < span class = "boring" > U: 'static + Display + Debug,
< / span > < span class = "boring" > {
< / span > < span class = "boring" > #[inline]
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< / span > < span class = "boring" > fn chain_error_from(t: T, line_filename: Option< String> ) -> ChainError< Self> {
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< / span > < span class = "boring" > let e: U = t.into();
< / span > < span class = "boring" > ChainError::new(e, None, line_filename)
< / span > < span class = "boring" > }
< / span > < span class = "boring" > }
< / span > < span class = "boring" >
< / span > < span class = "boring" > /// Convenience macro to create a " new type" T(String) and implement Display + Debug for T
< / span > < span class = "boring" > ///
< / span > < span class = "boring" > /// # Examples
< / span > < span class = "boring" > ///
< / span > < span class = "boring" > /// ```rust
< / span > < span class = "boring" > /// # use crate::chainerror::*;
< / span > < span class = "boring" > /// # use std::error::Error;
< / span > < span class = "boring" > /// # use std::io;
< / span > < span class = "boring" > /// # use std::result::Result;
< / span > < span class = "boring" > /// # fn do_some_io() -> Result< (), Box< dyn Error + Send + Sync> > {
< / span > < span class = "boring" > /// # Err(io::Error::from(io::ErrorKind::NotFound))?;
< / span > < span class = "boring" > /// # Ok(())
< / span > < span class = "boring" > /// # }
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< / span > < span class = "boring" > /// derive_str_context!(Func2Error);
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< / span > < span class = "boring" > ///
< / span > < span class = "boring" > /// fn func2() -> ChainResult< (), Func2Error> {
< / span > < span class = "boring" > /// let filename = " foo.txt" ;
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< / span > < span class = "boring" > /// do_some_io().context(Func2Error(format!(" Error reading '{}'" , filename)))?;
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< / span > < span class = "boring" > /// Ok(())
< / span > < span class = "boring" > /// }
< / span > < span class = "boring" > ///
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< / span > < span class = "boring" > /// derive_str_context!(Func1Error);
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< / span > < span class = "boring" > ///
< / span > < span class = "boring" > /// fn func1() -> Result< (), Box< dyn Error> > {
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< / span > < span class = "boring" > /// func2().context(Func1Error(" func1 error" .into()))?;
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< / span > < span class = "boring" > /// Ok(())
< / span > < span class = "boring" > /// }
< / span > < span class = "boring" > /// # if let Err(e) = func1() {
< / span > < span class = "boring" > /// # if let Some(f1err) = e.downcast_chain_ref::< Func1Error> () {
< / span > < span class = "boring" > /// # assert!(f1err.find_cause::< ChainError< Func2Error> > ().is_some());
< / span > < span class = "boring" > /// # assert!(f1err.find_chain_cause::< Func2Error> ().is_some());
< / span > < span class = "boring" > /// # } else {
< / span > < span class = "boring" > /// # panic!();
< / span > < span class = "boring" > /// # }
< / span > < span class = "boring" > /// # } else {
< / span > < span class = "boring" > /// # unreachable!();
< / span > < span class = "boring" > /// # }
< / span > < span class = "boring" > /// ```
< / span > < span class = "boring" > #[macro_export]
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< / span > < span class = "boring" > macro_rules! derive_str_context {
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< / span > < span class = "boring" > ($e:ident) => {
< / span > < span class = "boring" > #[derive(Clone)]
< / span > < span class = "boring" > pub struct $e(pub String);
< / span > < span class = "boring" > impl ::std::fmt::Display for $e {
< / span > < span class = "boring" > fn fmt(& self, f: & mut ::std::fmt::Formatter) -> ::std::fmt::Result {
< / span > < span class = "boring" > write!(f, " {}" , self.0)
< / span > < span class = "boring" > }
< / span > < span class = "boring" > }
< / span > < span class = "boring" > impl ::std::fmt::Debug for $e {
< / span > < span class = "boring" > fn fmt(& self, f: & mut ::std::fmt::Formatter) -> ::std::fmt::Result {
< / span > < span class = "boring" > write!(f, " {}({})" , stringify!($e), self.0)
< / span > < span class = "boring" > }
< / span > < span class = "boring" > }
< / span > < span class = "boring" > impl ::std::error::Error for $e {}
< / span > < span class = "boring" > };
< / span > < span class = "boring" > }
< / span > < span class = "boring" >
< / span > < span class = "boring" > /// Derive an Error for an ErrorKind, which wraps a `ChainError` and implements a `kind()` method
< / span > < span class = "boring" > ///
< / span > < span class = "boring" > /// It basically hides `ChainError` to the outside and only exposes the `kind()`
< / span > < span class = "boring" > /// method.
< / span > < span class = "boring" > ///
< / span > < span class = "boring" > /// Error::kind() returns the ErrorKind
< / span > < span class = "boring" > /// Error::source() returns the parent error
< / span > < span class = "boring" > ///
< / span > < span class = "boring" > /// # Examples
< / span > < span class = "boring" > ///
< / span > < span class = "boring" > /// ```rust
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< / span > < span class = "boring" > /// use chainerror::prelude::v1::*;
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< / span > < span class = "boring" > /// use std::io;
< / span > < span class = "boring" > ///
< / span > < span class = "boring" > /// fn do_some_io(_f: & str) -> std::result::Result< (), io::Error> {
< / span > < span class = "boring" > /// return Err(io::Error::from(io::ErrorKind::NotFound));
< / span > < span class = "boring" > /// }
< / span > < span class = "boring" > ///
< / span > < span class = "boring" > /// #[derive(Debug, Clone)]
< / span > < span class = "boring" > /// pub enum ErrorKind {
< / span > < span class = "boring" > /// IO(String),
< / span > < span class = "boring" > /// FatalError(String),
< / span > < span class = "boring" > /// Unknown,
< / span > < span class = "boring" > /// }
< / span > < span class = "boring" > ///
< / span > < span class = "boring" > /// derive_err_kind!(Error, ErrorKind);
< / span > < span class = "boring" > ///
< / span > < span class = "boring" > /// impl std::fmt::Display for ErrorKind {
< / span > < span class = "boring" > /// fn fmt(& self, f: & mut ::std::fmt::Formatter) -> std::fmt::Result {
< / span > < span class = "boring" > /// match self {
< / span > < span class = "boring" > /// ErrorKind::FatalError(e) => write!(f, " fatal error {}" , e),
< / span > < span class = "boring" > /// ErrorKind::Unknown => write!(f, " unknown error" ),
< / span > < span class = "boring" > /// ErrorKind::IO(filename) => write!(f, " Error reading '{}'" , filename),
< / span > < span class = "boring" > /// }
< / span > < span class = "boring" > /// }
< / span > < span class = "boring" > /// }
< / span > < span class = "boring" > ///
< / span > < span class = "boring" > /// impl ErrorKind {
< / span > < span class = "boring" > /// fn from_io_error(e: & io::Error, f: String) -> Self {
< / span > < span class = "boring" > /// match e.kind() {
< / span > < span class = "boring" > /// io::ErrorKind::BrokenPipe => panic!(" Should not happen" ),
< / span > < span class = "boring" > /// io::ErrorKind::ConnectionReset => {
< / span > < span class = "boring" > /// ErrorKind::FatalError(format!(" While reading `{}`: {}" , f, e))
< / span > < span class = "boring" > /// }
< / span > < span class = "boring" > /// _ => ErrorKind::IO(f),
< / span > < span class = "boring" > /// }
< / span > < span class = "boring" > /// }
< / span > < span class = "boring" > /// }
< / span > < span class = "boring" > ///
< / span > < span class = "boring" > /// impl From< & io::Error> for ErrorKind {
< / span > < span class = "boring" > /// fn from(e: & io::Error) -> Self {
< / span > < span class = "boring" > /// ErrorKind::IO(format!(" {}" , e))
< / span > < span class = "boring" > /// }
< / span > < span class = "boring" > /// }
< / span > < span class = "boring" > ///
< / span > < span class = "boring" > /// pub fn func1() -> std::result::Result< (), Error> {
< / span > < span class = "boring" > /// let filename = " bar.txt" ;
< / span > < span class = "boring" > ///
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< / span > < span class = "boring" > /// do_some_io(filename).map_context(|e| ErrorKind::from_io_error(e, filename.into()))?;
< / span > < span class = "boring" > /// do_some_io(filename).map_context(|e| ErrorKind::IO(filename.into()))?;
< / span > < span class = "boring" > /// do_some_io(filename).map_context(|e| ErrorKind::from(e))?;
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< / span > < span class = "boring" > /// Ok(())
< / span > < span class = "boring" > /// }
< / span > < span class = "boring" > /// ```
< / span > < span class = "boring" > #[macro_export]
< / span > < span class = "boring" > macro_rules! derive_err_kind {
< / span > < span class = "boring" > ($e:ident, $k:ident) => {
< / span > < span class = "boring" > pub struct $e($crate::ChainError< $k> );
< / span > < span class = "boring" >
< / span > < span class = "boring" > impl $e {
< / span > < span class = "boring" > pub fn kind(& self) -> & $k {
< / span > < span class = "boring" > self.0.kind()
< / span > < span class = "boring" > }
< / span > < span class = "boring" > }
< / span > < span class = "boring" >
< / span > < span class = "boring" > impl From< $k> for $e {
< / span > < span class = "boring" > fn from(e: $k) -> Self {
< / span > < span class = "boring" > $e($crate::ChainError::new(e, None, None))
< / span > < span class = "boring" > }
< / span > < span class = "boring" > }
< / span > < span class = "boring" >
< / span > < span class = "boring" > impl From< ChainError< $k> > for $e {
< / span > < span class = "boring" > fn from(e: $crate::ChainError< $k> ) -> Self {
< / span > < span class = "boring" > $e(e)
< / span > < span class = "boring" > }
< / span > < span class = "boring" > }
< / span > < span class = "boring" >
< / span > < span class = "boring" > impl From< & $e> for $k
< / span > < span class = "boring" > where
< / span > < span class = "boring" > $k: Clone,
< / span > < span class = "boring" > {
< / span > < span class = "boring" > fn from(e: & $e) -> Self {
< / span > < span class = "boring" > e.kind().clone()
< / span > < span class = "boring" > }
< / span > < span class = "boring" > }
< / span > < span class = "boring" >
< / span > < span class = "boring" > impl std::error::Error for $e {
< / span > < span class = "boring" > fn source(& self) -> Option< & (dyn std::error::Error + 'static)> {
< / span > < span class = "boring" > self.0.source()
< / span > < span class = "boring" > }
< / span > < span class = "boring" > }
< / span > < span class = "boring" >
< / span > < span class = "boring" > impl std::fmt::Display for $e {
< / span > < span class = "boring" > fn fmt(& self, f: & mut std::fmt::Formatter) -> std::fmt::Result {
< / span > < span class = "boring" > std::fmt::Display::fmt(& self.0, f)
< / span > < span class = "boring" > }
< / span > < span class = "boring" > }
< / span > < span class = "boring" >
< / span > < span class = "boring" > impl std::fmt::Debug for $e {
< / span > < span class = "boring" > fn fmt(& self, f: & mut std::fmt::Formatter) -> std::fmt::Result {
< / span > < span class = "boring" > std::fmt::Debug::fmt(& self.0, f)
< / span > < span class = "boring" > }
< / span > < span class = "boring" > }
< / span > < span class = "boring" > };
< / span > < span class = "boring" > }
< / span > < span class = "boring" > }
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< / span > < / code > < / pre > < / pre >
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< / main >
< nav class = "nav-wrapper" aria-label = "Page navigation" >
<!-- Mobile navigation buttons -->
< a rel = "prev" href = "tutorial6.html" class = "mobile-nav-chapters previous" title = "Previous chapter" aria-label = "Previous chapter" aria-keyshortcuts = "Left" >
< i class = "fa fa-angle-left" > < / i >
< / a >
< a rel = "next" href = "tutorial8.html" class = "mobile-nav-chapters next" title = "Next chapter" aria-label = "Next chapter" aria-keyshortcuts = "Right" >
< i class = "fa fa-angle-right" > < / i >
< / a >
< div style = "clear: both" > < / div >
< / nav >
< / div >
< / div >
< nav class = "nav-wide-wrapper" aria-label = "Page navigation" >
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< a rel = "prev" href = "tutorial6.html" class = "nav-chapters previous" title = "Previous chapter" aria-label = "Previous chapter" aria-keyshortcuts = "Left" >
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< i class = "fa fa-angle-left" > < / i >
< / a >
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< a rel = "next" href = "tutorial8.html" class = "nav-chapters next" title = "Next chapter" aria-label = "Next chapter" aria-keyshortcuts = "Right" >
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< i class = "fa fa-angle-right" > < / i >
< / a >
< / nav >
< / div >
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< script type = "text/javascript" >
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window.playground_copyable = true;
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< / script >
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< script src = "elasticlunr.min.js" type = "text/javascript" charset = "utf-8" > < / script >
< script src = "mark.min.js" type = "text/javascript" charset = "utf-8" > < / script >
< script src = "searcher.js" type = "text/javascript" charset = "utf-8" > < / script >
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< script src = "book.js" type = "text/javascript" charset = "utf-8" > < / script >
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< / html >
