Finding an Error cause
To distinguish the errors occuring in various places, we can define named string errors with the "new type" pattern.
derive_str_cherr!(Func2Error);
derive_str_cherr!(Func1Error);
Instead of ChainError<String> we now have struct Func1Error(String) and ChainError<Func1Error>.
In the main function you can see, how we can match the different errors.
Also see:
if let Some(f2err) = f1err.find_chain_cause::<Func2Error>() {
as a shortcut to
if let Some(f2err) = f1err.find_cause::<ChainError<Func2Error>>() {
hiding the ChainError<T> implementation detail.
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() -> Result<(), Box<Error>> { if let Err(e) = func1() { if let Some(f1err) = e.downcast_chain_ref::<Func1Error>() { eprintln!("Func1Error: {}", f1err); if let Some(f2err) = f1err.find_cause::<ChainError<Func2Error>>() { eprintln!("Func2Error: {}", f2err); } if let Some(f2err) = f1err.find_chain_cause::<Func2Error>() { eprintln!("Debug Func2Error:\n{:?}", f2err); } } } 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 {} # }; # } # }