2019-03-04 11:46:17 +01:00
<!DOCTYPE HTML>
2020-03-03 15:08:09 +01:00
< html lang = "en" class = "sidebar-visible no-js light" >
2019-03-04 11:46:17 +01:00
< head >
<!-- Book generated using mdBook -->
< meta charset = "UTF-8" >
< title > Writing a library - chainerror< / title >
2020-03-03 15:08:09 +01:00
2019-03-04 11:46:17 +01:00
< meta content = "text/html; charset=utf-8" http-equiv = "Content-Type" >
< meta name = "description" content = "A tutorial for the chainerror rust crate." >
< meta name = "viewport" content = "width=device-width, initial-scale=1" >
< meta name = "theme-color" content = "#ffffff" / >
< link rel = "shortcut icon" href = "favicon.png" >
< link rel = "stylesheet" href = "css/variables.css" >
< link rel = "stylesheet" href = "css/general.css" >
< link rel = "stylesheet" href = "css/chrome.css" >
< link rel = "stylesheet" href = "css/print.css" media = "print" >
<!-- Fonts -->
< link rel = "stylesheet" href = "FontAwesome/css/font-awesome.css" >
< link href = "https://fonts.googleapis.com/css?family=Open+Sans:300italic,400italic,600italic,700italic,800italic,400,300,600,700,800" rel = "stylesheet" type = "text/css" >
< link href = "https://fonts.googleapis.com/css?family=Source+Code+Pro:500" rel = "stylesheet" type = "text/css" >
<!-- Highlight.js Stylesheets -->
< link rel = "stylesheet" href = "highlight.css" >
< link rel = "stylesheet" href = "tomorrow-night.css" >
< link rel = "stylesheet" href = "ayu-highlight.css" >
<!-- Custom theme stylesheets -->
< / head >
2020-03-03 15:08:09 +01:00
< body >
2019-03-04 11:46:17 +01:00
<!-- Provide site root to javascript -->
< script type = "text/javascript" >
var path_to_root = "";
2020-03-03 15:08:09 +01:00
var default_theme = window.matchMedia("(prefers-color-scheme: dark)").matches ? "light" : "light";
2019-03-04 11:46:17 +01:00
< / script >
<!-- Work around some values being stored in localStorage wrapped in quotes -->
< script type = "text/javascript" >
try {
var theme = localStorage.getItem('mdbook-theme');
var sidebar = localStorage.getItem('mdbook-sidebar');
if (theme.startsWith('"') & & theme.endsWith('"')) {
localStorage.setItem('mdbook-theme', theme.slice(1, theme.length - 1));
}
if (sidebar.startsWith('"') & & sidebar.endsWith('"')) {
localStorage.setItem('mdbook-sidebar', sidebar.slice(1, sidebar.length - 1));
}
} catch (e) { }
< / script >
<!-- Set the theme before any content is loaded, prevents flash -->
< script type = "text/javascript" >
var theme;
2020-03-03 15:08:09 +01:00
try { theme = localStorage.getItem('mdbook-theme'); } catch(e) { }
2019-03-04 11:46:17 +01:00
if (theme === null || theme === undefined) { theme = default_theme; }
2020-03-03 15:08:09 +01:00
var html = document.querySelector('html');
html.classList.remove('no-js')
html.classList.remove('light')
html.classList.add(theme);
html.classList.add('js');
2019-03-04 11:46:17 +01:00
< / script >
<!-- Hide / unhide sidebar before it is displayed -->
< script type = "text/javascript" >
var html = document.querySelector('html');
var sidebar = 'hidden';
if (document.body.clientWidth >= 1080) {
try { sidebar = localStorage.getItem('mdbook-sidebar'); } catch(e) { }
sidebar = sidebar || 'visible';
}
html.classList.remove('sidebar-visible');
html.classList.add("sidebar-" + sidebar);
< / script >
< nav id = "sidebar" class = "sidebar" aria-label = "Table of contents" >
2020-03-03 15:08:09 +01:00
< div id = "sidebar-scrollbox" class = "sidebar-scrollbox" >
< 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" class = "active" > < 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 >
< / div >
< div id = "sidebar-resize-handle" class = "sidebar-resize-handle" > < / div >
2019-03-04 11:46:17 +01:00
< / nav >
< div id = "page-wrapper" class = "page-wrapper" >
< div class = "page" >
< div id = "menu-bar" class = "menu-bar" >
< div id = "menu-bar-sticky-container" >
< div class = "left-buttons" >
< button id = "sidebar-toggle" class = "icon-button" type = "button" title = "Toggle Table of Contents" aria-label = "Toggle Table of Contents" aria-controls = "sidebar" >
< i class = "fa fa-bars" > < / i >
< / button >
< button id = "theme-toggle" class = "icon-button" type = "button" title = "Change theme" aria-label = "Change theme" aria-haspopup = "true" aria-expanded = "false" aria-controls = "theme-list" >
< i class = "fa fa-paint-brush" > < / i >
< / button >
< ul id = "theme-list" class = "theme-popup" aria-label = "Themes" role = "menu" >
< li role = "none" > < button role = "menuitem" class = "theme" id = "light" > Light (default)< / button > < / li >
< li role = "none" > < button role = "menuitem" class = "theme" id = "rust" > Rust< / button > < / li >
< li role = "none" > < button role = "menuitem" class = "theme" id = "coal" > Coal< / button > < / li >
< li role = "none" > < button role = "menuitem" class = "theme" id = "navy" > Navy< / button > < / li >
< li role = "none" > < button role = "menuitem" class = "theme" id = "ayu" > Ayu< / button > < / li >
< / ul >
< button id = "search-toggle" class = "icon-button" type = "button" title = "Search. (Shortkey: s)" aria-label = "Toggle Searchbar" aria-expanded = "false" aria-keyshortcuts = "S" aria-controls = "searchbar" >
< i class = "fa fa-search" > < / i >
< / button >
< / div >
2020-03-03 15:08:09 +01:00
< h1 class = "menu-title" > chainerror< / h1 >
2019-03-04 11:46:17 +01:00
< div class = "right-buttons" >
< a href = "print.html" title = "Print this book" aria-label = "Print this book" >
< i id = "print-button" class = "fa fa-print" > < / i >
< / a >
< / div >
< / div >
< / div >
< div id = "search-wrapper" class = "hidden" >
< form id = "searchbar-outer" class = "searchbar-outer" >
< input type = "search" name = "search" id = "searchbar" name = "searchbar" placeholder = "Search this book ..." aria-controls = "searchresults-outer" aria-describedby = "searchresults-header" >
< / form >
< div id = "searchresults-outer" class = "searchresults-outer hidden" >
< div id = "searchresults-header" class = "searchresults-header" > < / div >
< ul id = "searchresults" >
< / ul >
< / div >
< / div >
<!-- Apply ARIA attributes after the sidebar and the sidebar toggle button are added to the DOM -->
< script type = "text/javascript" >
document.getElementById('sidebar-toggle').setAttribute('aria-expanded', sidebar === 'visible');
document.getElementById('sidebar').setAttribute('aria-hidden', sidebar !== 'visible');
Array.from(document.querySelectorAll('#sidebar a')).forEach(function(link) {
link.setAttribute('tabIndex', sidebar === 'visible' ? 0 : -1);
});
< / script >
< div id = "content" class = "content" >
< main >
2020-03-03 15:08:09 +01:00
< h1 > < a class = "header" href = "#writing-a-library" id = "writing-a-library" > Writing a library< / a > < / h1 >
2019-03-04 11:46:17 +01:00
< 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 >
2020-03-03 15:08:09 +01:00
< 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 {
2019-03-04 11:46:17 +01:00
use crate::chainerror::*; // omit the `crate::` part
use std::io;
2020-03-03 15:08:09 +01:00
fn do_some_io() -> std::result::Result< (), Box< std::error::Error + Send + Sync> > {
2019-03-04 11:46:17 +01:00
Err(io::Error::from(io::ErrorKind::NotFound))?;
Ok(())
}
derive_str_cherr!(Func2Error);
2020-03-03 15:08:09 +01:00
fn func2() -> std::result::Result< (), Box< std::error::Error + Send + Sync> > {
2019-03-04 11:46:17 +01:00
let filename = " foo.txt" ;
do_some_io().map_err(mstrerr!(Func2Error, " Error reading '{}'" , filename))?;
Ok(())
}
2020-03-03 15:08:09 +01:00
#[derive(Debug, Clone)]
2019-03-04 11:46:17 +01:00
pub enum ErrorKind {
Func2,
IO(String),
}
2020-03-03 15:08:09 +01:00
derive_err_kind!(Error, ErrorKind);
2019-03-04 11:46:17 +01:00
pub type Result< T> = std::result::Result< T, Error> ;
2020-03-03 15:08:09 +01:00
impl std::fmt::Display for ErrorKind {
fn fmt(& self, f: & mut ::std::fmt::Formatter) -> std::fmt::Result {
2019-03-04 11:46:17 +01:00
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(())
}
}
2020-03-03 15:08:09 +01:00
fn main() -> Result< (), Box< std::error::Error + Send + Sync> > {
2019-03-04 11:46:17 +01:00
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!();
2020-03-03 15:08:09 +01:00
let mut s: & Error = & e;
2019-03-04 11:46:17 +01:00
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 >
< / main >
< nav class = "nav-wrapper" aria-label = "Page navigation" >
<!-- Mobile navigation buttons -->
< a rel = "prev" href = "tutorial12.html" class = "mobile-nav-chapters previous" title = "Previous chapter" aria-label = "Previous chapter" aria-keyshortcuts = "Left" >
< i class = "fa fa-angle-left" > < / i >
< / a >
2020-03-03 15:08:09 +01:00
< a rel = "next" href = "tutorial14.html" class = "mobile-nav-chapters next" title = "Next chapter" aria-label = "Next chapter" aria-keyshortcuts = "Right" >
2019-03-04 11:46:17 +01:00
< 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" >
< a href = "tutorial12.html" class = "nav-chapters previous" title = "Previous chapter" aria-label = "Previous chapter" aria-keyshortcuts = "Left" >
< i class = "fa fa-angle-left" > < / i >
< / a >
2020-03-03 15:08:09 +01:00
< a href = "tutorial14.html" class = "nav-chapters next" title = "Next chapter" aria-label = "Next chapter" aria-keyshortcuts = "Right" >
2019-03-04 11:46:17 +01:00
< i class = "fa fa-angle-right" > < / i >
< / a >
< / nav >
< / div >
2020-03-03 15:08:09 +01:00
< script type = "text/javascript" >
window.playpen_copyable = true;
< / script >
2019-03-04 11:46:17 +01:00
< 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 >
< script src = "clipboard.min.js" type = "text/javascript" charset = "utf-8" > < / script >
< script src = "highlight.js" type = "text/javascript" charset = "utf-8" > < / script >
< script src = "book.js" type = "text/javascript" charset = "utf-8" > < / script >
<!-- Custom JS scripts -->
< / body >
< / html >
