The root cause of all Errors

chainerror also has some helper methods:

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

Using downcast_chain_ref::<String>() gives a ChainError<String>, which can be used to call .find_cause::<io::Error>().

        if let Some(s) = e.downcast_chain_ref::<String>() {
            if let Some(ioerror) = s.find_cause::<io::Error>() {

or to use .root_cause(), which of course can be of any type implementing std::error::Error.

            if let Some(e) = s.root_cause() {

use chainerror::*;
use std::error::Error;
use std::io;
use std::result::Result;

fn do_some_io() -> Result<(), Box<Error + Send + Sync>> {
    Err(io::Error::from(io::ErrorKind::NotFound))?;
    Ok(())
}

fn func2() -> Result<(), Box<Error + Send + Sync>> {
    let filename = "foo.txt";
    do_some_io().map_err(mstrerr!("Error reading '{}'", filename))?;
    Ok(())
}

fn func1() -> Result<(), Box<Error + Send + Sync>> {
    func2().map_err(mstrerr!("func1 error"))?;
    Ok(())
}

fn main() -> Result<(), Box<Error + Send + Sync>> {
    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);
            }
        }
    }
    Ok(())
}
#[allow(dead_code)]
mod chainerror {
{{#includecomment ../src/lib.rs}}
}