Mapping Errors
Now let's get more rust idiomatic by using .map_err().
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(()) } fn func2() -> Result<(), Box<Error>> { do_some_io().map_err(|e| cherr!(e, "func2 error"))?; Ok(()) } fn func1() -> Result<(), Box<Error>> { func2().map_err(|e| cherr!(e, "func1 error"))?; Ok(()) } fn main() -> Result<(), Box<Error>> { if let Err(e) = func1() { eprintln!("{:?}", e); } Ok(()) } # #[allow(dead_code)] # mod chainerror { # //! `chainerror` provides an error backtrace without doing a real backtrace, so even after you `strip` your # //! binaries, you still have the error backtrace. # //! # //! `chainerror` has no dependencies! # //! # //! `chainerror` uses `.source()` of `std::error::Error` along with `line()!` and `file()!` to provide a nice debug error backtrace. # //! It encapsulates all types, which have `Display + Debug` and can store the error cause internally. # //! # //! Along with the `ChainError<T>` struct, `chainerror` comes with some useful helper macros to save a lot of typing. # //! # //! ## Features # //! # //! `no-fileline` # //! : completely turn off storing filename and line # //! # //! `display-cause` # //! : turn on printing a backtrace of the errors in `Display` # //! # //! `no-debug-cause` # //! : turn off printing a backtrace of the errors in `Debug` # //! # //! # //! # Tutorial # //! # //! Read the [Tutorial](https://haraldh.github.io/chainerror/tutorial1.html) # //! # //! # Examples # //! # //! ~~~rust # //! use 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(()) # //! } # //! # //! fn func2() -> Result<(), Box<Error>> { # //! let filename = "foo.txt"; # //! do_some_io().map_err(mstrerr!("Error reading '{}'", filename))?; # //! Ok(()) # //! } # //! # //! fn func1() -> Result<(), Box<Error>> { # //! func2().map_err(mstrerr!("func1 error"))?; # //! Ok(()) # //! } # //! # //! fn main() { # //! if let Err(e) = func1() { # //! #[cfg(not(windows))] # //! assert_eq!( # //! format!("\n{:?}\n", e), r#" # //! src/lib.rs:20: func1 error # //! Caused by: # //! src/lib.rs:15: Error reading 'foo.txt' # //! Caused by: # //! Kind(NotFound) # //! "# # //! ); # //! } # //! # else { # //! # unreachable!(); # //! # } # //! } # //! ~~~ # //! # //! # //! ~~~rust # //! use 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(()) # //! } # //! # //! fn func3() -> Result<(), Box<Error>> { # //! let filename = "foo.txt"; # //! do_some_io().map_err(mstrerr!("Error reading '{}'", filename))?; # //! Ok(()) # //! } # //! # //! derive_str_cherr!(Func2Error); # //! # //! fn func2() -> ChainResult<(), Func2Error> { # //! func3().map_err(mstrerr!(Func2Error, "func2 error: calling func3"))?; # //! Ok(()) # //! } # //! # //! enum Func1Error { # //! Func2, # //! IO(String), # //! } # //! # //! impl ::std::fmt::Display for Func1Error { # //! fn fmt(&self, f: &mut ::std::fmt::Formatter) -> ::std::fmt::Result { # //! match self { # //! Func1Error::Func2 => write!(f, "func1 error calling func2"), # //! Func1Error::IO(filename) => write!(f, "Error reading '{}'", filename), # //! } # //! } # //! } # //! # //! impl ::std::fmt::Debug for Func1Error { # //! fn fmt(&self, f: &mut ::std::fmt::Formatter) -> ::std::fmt::Result { # //! write!(f, "{}", self) # //! } # //! } # //! # //! 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() { # //! if let Err(e) = func1() { # //! assert!( # //! match e.kind() { # //! Func1Error::Func2 => { # //! eprintln!("Main Error Report: func1 error calling func2"); # //! true # //! } # //! Func1Error::IO(filename) => { # //! eprintln!("Main Error Report: func1 error reading '{}'", filename); # //! false # //! } # //! } # //! ); # //! # //! assert!(e.find_chain_cause::<Func2Error>().is_some()); # //! # //! if let Some(e) = e.find_chain_cause::<Func2Error>() { # //! eprintln!("\nError reported by Func2Error: {}", e) # //! } # //! # //! # //! assert!(e.root_cause().is_some()); # //! # //! if let Some(e) = e.root_cause() { # //! let ioerror = e.downcast_ref::<io::Error>().unwrap(); # //! eprintln!("\nThe root cause was: std::io::Error: {:#?}", ioerror); # //! } # //! # //! #[cfg(not(windows))] # //! assert_eq!( # //! format!("\n{:?}\n", e), r#" # //! src/lib.rs:47: func1 error calling func2 # //! Caused by: # //! src/lib.rs:22: Func2Error(func2 error: calling func3) # //! Caused by: # //! src/lib.rs:15: Error reading 'foo.txt' # //! Caused by: # //! Kind(NotFound) # //! "# # //! ); # //! } # //! # else { # //! # unreachable!(); # //! # } # //! } # //! ~~~ # # use std::any::TypeId; # use std::error::Error; # use std::fmt::{Debug, Display, Formatter, Result}; # # /// chains an inner error kind `T` with a causing error # pub struct ChainError<T> { # #[cfg(not(feature = "no-fileline"))] # occurrence: Option<(u32, &'static str)>, # kind: T, # error_cause: Option<Box<dyn Error + 'static>>, # } # # /// convenience type alias # pub type ChainResult<O, E> = std::result::Result<O, ChainError<E>>; # # impl<T: 'static + Display + Debug> ChainError<T> { # #[cfg(not(feature = "no-fileline"))] # /// Use the `cherr!()` or `mstrerr!()` macro instead of calling this directly # 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")] # /// Use the `cherr!()` or `mstrerr!()` macro instead of calling this directly # pub fn new( # kind: T, # error_cause: Option<Box<dyn Error + 'static>>, # _occurrence: Option<(u32, &'static str)>, # ) -> Self { # Self { kind, error_cause } # } # # /// return the root cause of the error chain, if any exists # pub fn root_cause(&self) -> Option<&(dyn Error + 'static)> { # self.iter().last() # } # # /// Find the first error cause of type U, if any exists # /// # /// # Examples # /// # /// ~~~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_str_cherr!(Func1Error); # /// # /// fn func1() -> Result<(), Box<Error>> { # /// func2().map_err(mstrerr!(Func1Error, "func1 error"))?; # /// Ok(()) # /// } # /// # /// fn main() { # /// if let Err(e) = func1() { # /// if let Some(f1err) = e.downcast_chain_ref::<Func1Error>() { # /// # /// assert!(f1err.find_cause::<io::Error>().is_some()); # /// # /// assert!(f1err.find_chain_cause::<Func2Error>().is_some()); # /// } # /// # else { # /// # panic!(); # /// # } # /// } # /// # else { # /// # unreachable!(); # /// # } # /// } # /// ~~~ # pub fn find_cause<U: Error + 'static>(&self) -> Option<&U> { # self.iter().filter_map(Error::downcast_ref::<U>).next() # } # # /// Find the first error cause of type `ChainError<U>`, if any exists # /// # /// Same as `find_cause`, but hides the `ChainError<U>` implementation internals # /// # /// # Examples # /// # /// ~~~rust,ignore # /// // Instead of writing # /// err.find_cause::<ChainError<FooError>>(); # /// # /// // leave out the ChainError<FooError> implementation detail # /// err.find_chain_cause::<FooError>(); # /// ~~~ # pub fn find_chain_cause<U: Error + 'static>(&self) -> Option<&ChainError<U>> { # self.iter() # .filter_map(Error::downcast_ref::<ChainError<U>>) # .next() # } # # /// Find the first error cause of type `ChainError<U>` or `U`, if any exists and return `U` # /// # /// Same as `find_cause` and `find_chain_cause`, but hides the `ChainError<U>` implementation internals # /// # /// # Examples # /// # /// ~~~rust,ignore # /// // Instead of writing # /// err.find_cause::<ChainError<FooErrorKind>>(); # /// // and/or # /// err.find_chain_cause::<FooErrorKind>(); # /// // and/or # /// err.find_cause::<FooErrorKind>(); # /// # /// // leave out the ChainError<FooErrorKind> implementation detail # /// err.find_chain_or_kind::<FooErrorKind>(); # /// ~~~ # pub fn find_kind_or_cause<U: Error + 'static>(&self) -> Option<&U> { # self.iter() # .filter_map(|e| { # e.downcast_ref::<ChainError<U>>() # .map(|e| e.kind()) # .or_else(|| e.downcast_ref::<U>()) # }) # .next() # } # # /// Return a reference to T of `ChainError<T>` # /// # /// # Examples # /// # /// ~~~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 Func1ErrorKind { # /// Func2, # /// IO(String), # /// } # /// # /// /// impl ::std::fmt::Display for Func1ErrorKind {…} # /// # impl ::std::fmt::Display for Func1ErrorKind { # /// # fn fmt(&self, f: &mut ::std::fmt::Formatter) -> ::std::fmt::Result { # /// # match self { # /// # Func1ErrorKind::Func2 => write!(f, "func1 error calling func2"), # /// # Func1ErrorKind::IO(filename) => write!(f, "Error reading '{}'", filename), # /// # } # /// # } # /// # } # /// # /// fn func1() -> ChainResult<(), Func1ErrorKind> { # /// func2().map_err(|e| cherr!(e, Func1ErrorKind::Func2))?; # /// do_some_io().map_err(|e| cherr!(e, Func1ErrorKind::IO("bar.txt".into())))?; # /// Ok(()) # /// } # /// # /// fn main() { # /// if let Err(e) = func1() { # /// match e.kind() { # /// Func1ErrorKind::Func2 => {}, # /// Func1ErrorKind::IO(filename) => panic!(), # /// } # /// } # /// # else { # /// # unreachable!(); # /// # } # /// } # /// ~~~ # pub fn kind(&self) -> &T { # &self.kind # } # # /// Returns an Iterator over all error causes/sources # /// # /// # Example # /// # /// # pub fn iter(&self) -> impl Iterator<Item = &(dyn Error + 'static)> { # ErrorIter { # current: Some(self), # } # } # } # # struct ErrorIter<'a> { # current: Option<&'a (dyn Error + 'static)>, # } # # impl<'a> Iterator for ErrorIter<'a> { # type Item = &'a (dyn Error + 'static); # # fn next(&mut self) -> Option<Self::Item> { # let current = self.current; # self.current = self.current.and_then(Error::source); # current # } # } # # impl<T: 'static + Display + Debug> std::ops::Deref for ChainError<T> { # type Target = T; # # fn deref(&self) -> &Self::Target { # &self.kind # } # } # # /// Convenience trait to hide the `ChainError<T>` implementation internals # pub trait ChainErrorDown { # /// Test if of type `ChainError<T>` # fn is_chain<T: 'static + Display + Debug>(&self) -> bool; # /// Downcast to a reference of `ChainError<T>` # fn downcast_chain_ref<T: 'static + Display + Debug>(&self) -> Option<&ChainError<T>>; # /// Downcast to a mutable reference of `ChainError<T>` # fn downcast_chain_mut<T: 'static + Display + Debug>(&mut self) -> Option<&mut ChainError<T>>; # } # # 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>() { # #[allow(clippy::cast_ptr_alignment)] # 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>() { # #[allow(clippy::cast_ptr_alignment)] # 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)> { # self.error_cause.as_ref().map(|e| e.as_ref()) # } # } # # impl<T: 'static + Display + Debug> Error for &ChainError<T> { # fn source(&self) -> Option<&(dyn Error + 'static)> { # self.error_cause.as_ref().map(|e| e.as_ref()) # } # } # # impl<T: 'static + Display + Debug> Error for &mut ChainError<T> { # fn source(&self) -> Option<&(dyn Error + 'static)> { # self.error_cause.as_ref().map(|e| e.as_ref()) # } # } # # 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)?; # } # } # # if self.is_chain::<String>() { # Display::fmt(&self.kind, f)?; # } else { # 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(()) # } # } # # pub trait ChainErrorFrom<T>: Sized { # fn chain_error_from(_: T, line_filename: Option<(u32, &'static str)>) -> ChainError<Self>; # } # # pub trait IntoChainError<T>: Sized { # fn into_chain_error(self, line_filename: Option<(u32, &'static str)>) -> ChainError<T>; # } # # impl<T, U> IntoChainError<U> for T # where # U: ChainErrorFrom<T>, # { # fn into_chain_error(self, line_filename: Option<(u32, &'static str)>) -> ChainError<U> { # U::chain_error_from(self, line_filename) # } # } # # impl<T, U> ChainErrorFrom<T> for U # where # T: Into<U>, # U: 'static + Display + Debug, # { # fn chain_error_from(t: T, line_filename: Option<(u32, &'static str)>) -> ChainError<Self> { # let e: U = t.into(); # ChainError::<_>::new(e, None, line_filename) # } # } # # #[macro_export] # macro_rules! minto_cherr { # ( ) => { # |e| e.into_chain_error(Some((line!(), file!()))) # }; # } # # #[macro_export] # macro_rules! into_cherr { # ( $t:expr ) => { # $t.into_chain_error(Some((line!(), file!()))) # }; # } # # /// Creates a new `ChainError<T>` # /// # /// # Examples # /// # /// Create a new ChainError<FooError>, where `FooError` must implement `Display` and `Debug`. # /// ~~~rust # /// # use chainerror::*; # /// # # /// # #[derive(Debug)] # /// enum FooError { # /// Bar, # /// Baz(&'static str), # /// } # /// # # /// # impl ::std::fmt::Display for FooError { # /// # fn fmt(&self, f: &mut ::std::fmt::Formatter) -> ::std::fmt::Result { # /// # match self { # /// # FooError::Bar => write!(f, "Bar Error"), # /// # FooError::Baz(s) => write!(f, "Baz Error: '{}'", s), # /// # } # /// # } # /// # } # /// # /// // impl ::std::fmt::Display for FooError # /// # /// fn do_some_stuff() -> bool { # /// false # /// } # /// # /// fn func() -> ChainResult<(), FooError> { # /// if ! do_some_stuff() { # /// Err(cherr!(FooError::Baz("Error")))?; # /// } # /// Ok(()) # /// } # /// # # /// # pub fn main() { # /// # match func().unwrap_err().kind() { # /// # FooError::Baz(s) if s == &"Error" => {}, # /// # _ => panic!(), # /// # } # /// # } # /// ~~~ # /// # /// Additionally an error cause can be added. # /// # /// ~~~rust # /// # use chainerror::*; # /// # use std::io; # /// # use std::error::Error; # /// # # /// # #[derive(Debug)] # /// # enum FooError { # /// # Bar, # /// # Baz(&'static str), # /// # } # /// # # /// # impl ::std::fmt::Display for FooError { # /// # fn fmt(&self, f: &mut ::std::fmt::Formatter) -> ::std::fmt::Result { # /// # match self { # /// # FooError::Bar => write!(f, "Bar Error"), # /// # FooError::Baz(s) => write!(f, "Baz Error: '{}'", s), # /// # } # /// # } # /// # } # /// # # /// fn do_some_stuff() -> Result<(), Box<Error>> { # /// Err(io::Error::from(io::ErrorKind::NotFound))?; # /// Ok(()) # /// } # /// # /// fn func() -> ChainResult<(), FooError> { # /// do_some_stuff().map_err( # /// |e| cherr!(e, FooError::Baz("Error")) # /// )?; # /// Ok(()) # /// } # /// # # /// # pub fn main() { # /// # match func().unwrap_err().kind() { # /// # FooError::Baz(s) if s == &"Error" => {}, # /// # _ => panic!(), # /// # } # /// # } # /// ~~~ # #[macro_export] # macro_rules! cherr { # ( $k:expr ) => ({ # ChainError::<_>::new($k, None, Some((line!(), file!()))) # }); # ( None, $k:expr ) => ({ # ChainError::<_>::new($k, None, Some((line!(), file!()))) # }); # ( None, $fmt:expr, $($arg:tt)+ ) => ({ # cherr!(None, format!($fmt, $($arg)+ )) # }); # ( None, $fmt:expr, $($arg:tt)+ ) => ({ # cherr!(None, format!($fmt, $($arg)+ )) # }); # ( $e:ident, $k:expr ) => ({ # ChainError::<_>::new($k, Some(Box::from($e)), Some((line!(), file!()))) # }); # ( $e:path, $k:expr ) => ({ # ChainError::<_>::new($k, Some(Box::from($e)), Some((line!(), file!()))) # }); # ( $e:ident, $fmt:expr, $($arg:tt)+ ) => ({ # cherr!($e, format!($fmt, $($arg)+ )) # }); # ( $e:path, $fmt:expr, $($arg:tt)+ ) => ({ # cherr!($e, format!($fmt, $($arg)+ )) # }); # # } # # /// Convenience macro for `|e| cherr!(e, format!(…))` # /// # /// # Examples # /// # /// ~~~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(()) # /// # } # /// # # /// fn func2() -> Result<(), Box<Error>> { # /// let filename = "foo.txt"; # /// do_some_io().map_err(mstrerr!("Error reading '{}'", filename))?; # /// Ok(()) # /// } # /// # /// fn func1() -> Result<(), Box<Error>> { # /// func2().map_err(mstrerr!("func1 error"))?; # /// Ok(()) # /// } # /// # /// # fn main() { # /// # if let Err(e) = func1() { # /// # #[cfg(not(windows))] # /// # assert_eq!( # /// # format!("\n{:?}\n", e), r#" # /// # src/lib.rs:20: func1 error # /// # Caused by: # /// # src/lib.rs:15: Error reading 'foo.txt' # /// # Caused by: # /// # Kind(NotFound) # /// # "# # /// # ); # /// # } else { # /// # unreachable!(); # /// # } # /// # } # /// ~~~ # /// # /// `mstrerr!()` can also be used to map a new `ChainError<T>`, where T was defined with # /// `derive_str_cherr!(T)` # /// # /// ~~~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_str_cherr!(Func1Error); # /// # /// fn func1() -> Result<(), Box<Error>> { # /// func2().map_err(mstrerr!(Func1Error, "func1 error"))?; # /// Ok(()) # /// } # /// # # /// # fn main() { # /// # if let Err(e) = func1() { # /// # if let Some(f1err) = e.downcast_chain_ref::<Func1Error>() { # /// # assert!(f1err.find_cause::<ChainError<Func2Error>>().is_some()); # /// # assert!(f1err.find_chain_cause::<Func2Error>().is_some()); # /// # } else { # /// # panic!(); # /// # } # /// # } else { # /// # unreachable!(); # /// # } # /// # } # /// ~~~ # #[macro_export] # macro_rules! mstrerr { # ( $t:ident, $msg:expr ) => ({ # |e| cherr!(e, $t ($msg.to_string())) # }); # ( $t:path, $msg:expr ) => ({ # |e| cherr!(e, $t ($msg.to_string())) # }); # ( $t:ident, $msg:expr, ) => ({ # |e| cherr!(e, $t ($msg.to_string())) # }); # ( $t:path, $msg:expr, ) => ({ # |e| cherr!(e, $t ($msg.to_string())) # }); # ( $t:ident, $fmt:expr, $($arg:tt)+ ) => ({ # |e| cherr!(e, $t (format!($fmt, $($arg)+ ))) # }); # ( $t:path, $fmt:expr, $($arg:tt)+ ) => ({ # |e| cherr!(e, $t (format!($fmt, $($arg)+ ))) # }); # ($msg:expr) => ({ # |e| cherr!(e, $msg.to_string()) # }); # ($msg:expr, ) => ({ # |e| cherr!(e, $msg.to_string()) # }); # ($fmt:expr, $($arg:tt)+) => ({ # |e| cherr!(e, format!($fmt, $($arg)+ )) # }); # } # # /// Convenience macro for `cherr!(T(format!(…)))` where `T(String)` # /// # /// # Examples # /// # /// ~~~rust # /// # use crate::chainerror::*; # /// # use std::error::Error; # /// # use std::result::Result; # /// # # /// derive_str_cherr!(Func2Error); # /// # /// fn func2() -> ChainResult<(), Func2Error> { # /// let filename = "foo.txt"; # /// Err(strerr!(Func2Error, "Error reading '{}'", filename)) # /// } # /// # /// derive_str_cherr!(Func1Error); # /// # /// fn func1() -> Result<(), Box<Error>> { # /// func2().map_err(mstrerr!(Func1Error, "func1 error"))?; # /// Ok(()) # /// } # /// # # /// # fn main() { # /// # if let Err(e) = func1() { # /// # if let Some(f1err) = e.downcast_chain_ref::<Func1Error>() { # /// # assert!(f1err.find_cause::<ChainError<Func2Error>>().is_some()); # /// # assert!(f1err.find_chain_cause::<Func2Error>().is_some()); # /// # } else { # /// # panic!(); # /// # } # /// # } else { # /// # unreachable!(); # /// # } # /// # } # /// ~~~ # #[macro_export] # macro_rules! strerr { # ( $t:ident, $msg:expr ) => ({ # cherr!($t ($msg.to_string())) # }); # ( $t:path, $msg:expr ) => ({ # cherr!($t ($msg.to_string())) # }); # ( $t:ident, $msg:expr, ) => ({ # cherr!($t ($msg.to_string())) # }); # ( $t:path, $msg:expr, ) => ({ # cherr!($t ($msg.to_string())) # }); # ( $t:ident, $fmt:expr, $($arg:tt)+ ) => ({ # cherr!($t (format!($fmt, $($arg)+ ))) # }); # ( $t:path, $fmt:expr, $($arg:tt)+ ) => ({ # cherr!($t (format!($fmt, $($arg)+ ))) # }); # ($msg:expr) => ({ # cherr!($msg.to_string()) # }); # ($msg:expr, ) => ({ # cherr!($msg.to_string()) # }); # ($fmt:expr, $($arg:tt)+) => ({ # cherr!(format!($fmt, $($arg)+ )) # }); # } # # /// Convenience macro to create a "new type" T(String) and implement Display + Debug for T # /// # /// # Examples # /// # /// ~~~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() -> ChainResult<(), Func2Error> { # /// let filename = "foo.txt"; # /// do_some_io().map_err(mstrerr!(Func2Error, "Error reading '{}'", filename))?; # /// Ok(()) # /// } # /// # /// derive_str_cherr!(Func1Error); # /// # /// fn func1() -> Result<(), Box<Error>> { # /// func2().map_err(mstrerr!(Func1Error, "func1 error"))?; # /// Ok(()) # /// } # /// # # /// # fn main() { # /// # if let Err(e) = func1() { # /// # if let Some(f1err) = e.downcast_chain_ref::<Func1Error>() { # /// # assert!(f1err.find_cause::<ChainError<Func2Error>>().is_some()); # /// # assert!(f1err.find_chain_cause::<Func2Error>().is_some()); # /// # } else { # /// # panic!(); # /// # } # /// # } else { # /// # unreachable!(); # /// # } # /// # } # /// ~~~ # #[macro_export] # macro_rules! derive_str_cherr { # ($e:ident) => { # pub struct $e(pub 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 {} # }; # } # }
If you compare the output to the previous example, you will see, that:
Error: src/main.rs:19: "func1 error"
changed to just:
src/main.rs:16: "func1 error"
This is, because we caught the error of func1() in main() and print it out ourselves.
We can now control, whether to output in Debug or Display mode.
Maybe depending on --debug as a CLI argument.