<!DOCTYPE HTML> <html lang="en" class="sidebar-visible no-js"> <head> <!-- Book generated using mdBook --> <meta charset="UTF-8"> <title>Chapter 10 - chainerror</title> <meta content="text/html; charset=utf-8" http-equiv="Content-Type"> <meta name="description" content=""> <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> <body class="light"> <!-- Provide site root to javascript --> <script type="text/javascript"> var path_to_root = ""; var default_theme = "light"; </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; try { theme = localStorage.getItem('mdbook-theme'); } catch(e) { } if (theme === null || theme === undefined) { theme = default_theme; } document.body.className = theme; document.querySelector('html').className = theme + ' js'; </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"> <ol class="chapter"><li><a href="tutorial1.html"><strong aria-hidden="true">1.</strong> Chapter 1</a></li><li><a href="tutorial2.html"><strong aria-hidden="true">2.</strong> Chapter 2</a></li><li><a href="tutorial3.html"><strong aria-hidden="true">3.</strong> Chapter 3</a></li><li><a href="tutorial4.html"><strong aria-hidden="true">4.</strong> Chapter 4</a></li><li><a href="tutorial5.html"><strong aria-hidden="true">5.</strong> Chapter 5</a></li><li><a href="tutorial6.html"><strong aria-hidden="true">6.</strong> Chapter 6</a></li><li><a href="tutorial7.html"><strong aria-hidden="true">7.</strong> Chapter 7</a></li><li><a href="tutorial8.html"><strong aria-hidden="true">8.</strong> Chapter 8</a></li><li><a href="tutorial9.html"><strong aria-hidden="true">9.</strong> Chapter 9</a></li><li><a href="tutorial10.html" class="active"><strong aria-hidden="true">10.</strong> Chapter 10</a></li><li><a href="tutorial11.html"><strong aria-hidden="true">11.</strong> Chapter 11</a></li></ol> </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> <h1 class="menu-title">chainerror</h1> <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> <pre><pre class="playpen"><code class="language-rust">use crate::chainerror::*; use std::error::Error; use std::io; use std::result::Result; fn do_some_io() -> Result<(), Box<Error>> { Err(io::Error::from(io::ErrorKind::NotFound))?; Ok(()) } derive_str_cherr!(Func2Error); fn func2() -> Result<(), Box<Error>> { let filename = "foo.txt"; do_some_io().map_err(mstrerr!(Func2Error, "Error reading '{}'", filename))?; Ok(()) } #[derive(Debug)] 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), } } } fn func1() -> ChainResult<(), Func1Error> { func2().map_err(|e| cherr!(e, Func1Error::Func2))?; let filename = String::from("bar.txt"); do_some_io().map_err(|e| cherr!(e, Func1Error::IO(filename)))?; Ok(()) } fn main() -> Result<(), Box<Error>> { 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!("Error reported by Func2Error: {}", e) } eprintln!("\nDebug Error:\n{:?}", e); } Ok(()) } # #[allow(dead_code)] # mod chainerror { # use std::error::Error; # use std::fmt::{Debug, Display, Formatter, Result}; # use std::result::Result as StdResult; # # pub struct ChainError<T> { # #[cfg(not(feature = "no-fileline"))] # occurrence: Option<(u32, &'static str)>, # kind: T, # error_cause: Option<Box<dyn Error + 'static>>, # } # # pub type ChainResult<O, E> = StdResult<O, ChainError<E>>; # # impl<T: 'static + Display + Debug> ChainError<T> { # #[cfg(not(feature = "no-fileline"))] # pub fn new( # kind: T, # error_cause: Option<Box<dyn Error + 'static>>, # occurrence: Option<(u32, &'static str)>, # ) -> Self { # Self { # occurrence, # kind, # error_cause, # } # } # # #[cfg(feature = "no-fileline")] # pub fn new( # kind: T, # error_cause: Option<Box<dyn Error + 'static>>, # _occurrence: Option<(u32, &'static str)>, # ) -> Self { # Self { kind, error_cause } # } # # pub fn root_cause(&self) -> Option<&(dyn Error + 'static)> { # let mut cause = self as &(dyn Error + 'static); # while let Some(c) = cause.source() { # cause = c; # } # Some(cause) # } # # pub fn find_cause<U: Error + 'static>(&self) -> Option<&U> { # let mut cause = self as &(dyn Error + 'static); # loop { # if cause.is::<U>() { # return cause.downcast_ref::<U>(); # } # # match cause.source() { # Some(c) => cause = c, # None => return None, # } # } # } # # pub fn find_chain_cause<U: Error + 'static>(&self) -> Option<&ChainError<U>> { # let mut cause = self as &(dyn Error + 'static); # loop { # if cause.is::<ChainError<U>>() { # return cause.downcast_ref::<ChainError<U>>(); # } # # match cause.source() { # Some(c) => cause = c, # None => return None, # } # } # } # # pub fn kind<'a>(&'a self) -> &'a T { # &self.kind # } # } # # pub trait ChainErrorDown { # 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>>; # } # # use std::any::TypeId; # # impl<U: 'static + Display + Debug> ChainErrorDown for ChainError<U> { # fn is_chain<T: 'static + Display + Debug>(&self) -> bool { # TypeId::of::<T>() == TypeId::of::<U>() # } # # fn downcast_chain_ref<T: 'static + Display + Debug>(&self) -> Option<&ChainError<T>> { # if self.is_chain::<T>() { # unsafe { Some(&*(self as *const dyn Error as *const &ChainError<T>)) } # } else { # None # } # } # # fn downcast_chain_mut<T: 'static + Display + Debug>(&mut self) -> Option<&mut ChainError<T>> { # if self.is_chain::<T>() { # unsafe { Some(&mut *(self as *mut dyn Error as *mut &mut ChainError<T>)) } # } else { # None # } # } # } # # impl ChainErrorDown for dyn Error + 'static { # fn is_chain<T: 'static + Display + Debug>(&self) -> bool { # self.is::<ChainError<T>>() # } # # fn downcast_chain_ref<T: 'static + Display + Debug>(&self) -> Option<&ChainError<T>> { # self.downcast_ref::<ChainError<T>>() # } # # fn downcast_chain_mut<T: 'static + Display + Debug>(&mut self) -> Option<&mut ChainError<T>> { # self.downcast_mut::<ChainError<T>>() # } # } # # impl ChainErrorDown for dyn Error + 'static + Send { # fn is_chain<T: 'static + Display + Debug>(&self) -> bool { # self.is::<ChainError<T>>() # } # # fn downcast_chain_ref<T: 'static + Display + Debug>(&self) -> Option<&ChainError<T>> { # self.downcast_ref::<ChainError<T>>() # } # # fn downcast_chain_mut<T: 'static + Display + Debug>(&mut self) -> Option<&mut ChainError<T>> { # self.downcast_mut::<ChainError<T>>() # } # } # # impl ChainErrorDown for dyn Error + 'static + Send + Sync { # fn is_chain<T: 'static + Display + Debug>(&self) -> bool { # self.is::<ChainError<T>>() # } # # fn downcast_chain_ref<T: 'static + Display + Debug>(&self) -> Option<&ChainError<T>> { # self.downcast_ref::<ChainError<T>>() # } # # fn downcast_chain_mut<T: 'static + Display + Debug>(&mut self) -> Option<&mut ChainError<T>> { # self.downcast_mut::<ChainError<T>>() # } # } # # impl<T: 'static + Display + Debug> Error for ChainError<T> { # fn source(&self) -> Option<&(dyn Error + 'static)> { # if let Some(ref e) = self.error_cause { # Some(e.as_ref()) # } else { # None # } # } # } # # impl<T: 'static + Display + Debug> Error for &ChainError<T> { # fn source(&self) -> Option<&(dyn Error + 'static)> { # if let Some(ref e) = self.error_cause { # Some(e.as_ref()) # } else { # None # } # } # } # # impl<T: 'static + Display + Debug> Error for &mut ChainError<T> { # fn source(&self) -> Option<&(dyn Error + 'static)> { # if let Some(ref e) = self.error_cause { # Some(e.as_ref()) # } else { # None # } # } # } # # impl<T: 'static + Display + Debug> Display for ChainError<T> { # fn fmt(&self, f: &mut Formatter) -> Result { # write!(f, "{}", self.kind)?; # # #[cfg(feature = "display-cause")] # { # if let Some(e) = self.source() { # writeln!(f, "\nCaused by:")?; # Display::fmt(&e, f)?; # } # } # Ok(()) # } # } # # impl<T: 'static + Display + Debug> Debug for ChainError<T> { # fn fmt(&self, f: &mut Formatter) -> Result { # #[cfg(not(feature = "no-fileline"))] # { # if let Some(o) = self.occurrence { # write!(f, "{}:{}: ", o.1, o.0)?; # } # } # # Debug::fmt(&self.kind, f)?; # # #[cfg(not(feature = "no-debug-cause"))] # { # if let Some(e) = self.source() { # writeln!(f, "\nCaused by:")?; # Debug::fmt(&e, f)?; # } # } # Ok(()) # } # } # # #[macro_export] # macro_rules! cherr { # ( $k:expr ) => { # ChainError::<_>::new($k, None, Some((line!(), file!()))) # }; # ( $e:expr, $k:expr ) => { # ChainError::<_>::new($k, Some(Box::from($e)), Some((line!(), file!()))) # }; # } # # #[macro_export] # macro_rules! mstrerr { # ( $t:ident, $v:expr $(, $more:expr)* ) => { # |e| cherr!(e, $t (format!($v, $( $more , )* ))) # }; # ( $t:path, $v:expr $(, $more:expr)* ) => { # |e| cherr!(e, $t (format!($v, $( $more , )* ))) # }; # ( $v:expr $(, $more:expr)* ) => { # |e| cherr!(e, format!($v, $( $more , )* )) # }; # } # # #[macro_export] # macro_rules! derive_str_cherr { # ($e:ident) => { # struct $e(String); # impl ::std::fmt::Display for $e { # fn fmt(&self, f: &mut ::std::fmt::Formatter) -> ::std::fmt::Result { # write!(f, "{}", self.0) # } # } # impl ::std::fmt::Debug for $e { # fn fmt(&self, f: &mut ::std::fmt::Formatter) -> ::std::fmt::Result { # write!(f, "{}({})", stringify!($e), self.0) # } # } # impl ::std::error::Error for $e {} # }; # } # # #[macro_export] # macro_rules! try_cherr_ref { # ( $e:expr, $t:ident ) => { # $e.downcast_ref::<ChainError<$t>>() # }; # ( $e:expr, $t:path ) => { # $e.downcast_ref::<ChainError<$t>>() # }; # } # # #[macro_export] # macro_rules! try_cherr_mut { # ( $e:expr, $t:ident ) => { # $e.downcast_mut::<ChainError<$t>>() # }; # ( $e:expr, $t:path ) => { # $e.downcast_mut::<ChainError<$t>>() # }; # } # } </code></pre></pre> </main> <nav class="nav-wrapper" aria-label="Page navigation"> <!-- Mobile navigation buttons --> <a rel="prev" href="tutorial9.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="tutorial11.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"> <a href="tutorial9.html" class="nav-chapters previous" title="Previous chapter" aria-label="Previous chapter" aria-keyshortcuts="Left"> <i class="fa fa-angle-left"></i> </a> <a href="tutorial11.html" class="nav-chapters next" title="Next chapter" aria-label="Next chapter" aria-keyshortcuts="Right"> <i class="fa fa-angle-right"></i> </a> </nav> </div> <script src="ace.js" type="text/javascript" charset="utf-8"></script> <script src="editor.js" type="text/javascript" charset="utf-8"></script> <script src="mode-rust.js" type="text/javascript" charset="utf-8"></script> <script src="theme-dawn.js" type="text/javascript" charset="utf-8"></script> <script src="theme-tomorrow_night.js" type="text/javascript" charset="utf-8"></script> <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>