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// Simple and robust error handling with error-chain!
// Use this as a template for new projects.
// `error_chain!` can recurse deeply
#![recursion_limit = "1024"]
// Import the macro. Don't forget to add `error-chain` in your
// `Cargo.toml`!
extern crate error_chain;
// We'll put our errors in an `errors` module, and other modules in
// this crate will `use errors::*;` to get access to everything
// `error_chain!` creates.
mod errors {
// Create the Error, ErrorKind, ResultExt, and Result types
// This only gives access within this module. Make this `pub use errors::*;`
// instead if the types must be accessible from other modules (e.g., within
// a `links` section).
use errors::*;
fn main() {
if let Err(ref e) = run() {
use std::io::Write;
let stderr = &mut ::std::io::stderr();
let errmsg = "Error writing to stderr";
writeln!(stderr, "error: {}", e).expect(errmsg);
for e in e.iter().skip(1) {
writeln!(stderr, "caused by: {}", e).expect(errmsg);
// The backtrace is not always generated. Try to run this example
// with `RUST_BACKTRACE=1`.
if let Some(backtrace) = e.backtrace() {
writeln!(stderr, "backtrace: {:?}", backtrace).expect(errmsg);
// The above main gives you maximum control over how the error is
// formatted. If you don't care (i.e. you want to display the full
// error during an assert) you can just call the `display_chain` method
// on the error object
fn alternative_main() {
if let Err(ref e) = run() {
use std::io::Write;
use error_chain::ChainedError; // trait which holds `display_chain`
let stderr = &mut ::std::io::stderr();
let errmsg = "Error writing to stderr";
writeln!(stderr, "{}", e.display_chain()).expect(errmsg);
// Use this macro to auto-generate the main above. You may want to
// set the `RUST_BACKTRACE` env variable to see a backtrace.
// quick_main!(run);
// Most functions will return the `Result` type, imported from the
// `errors` module. It is a typedef of the standard `Result` type
// for which the error type is always our own `Error`.
fn run() -> Result<()> {
use std::fs::File;
// This operation will fail
.chain_err(|| "unable to open tretrete file")?;