Code shared from the Rust Playground

playground.rs

use std::io;
use std::io::Read;
use std::fs::File;
use std::path::Path;
use std::num::ParseIntError;
use failure::Fail;

fn do_io_things(file: &Path) -> Result<i32, Error> {
    let mut file = File::open(file)?;
    let mut contents = String::new();
    file.read_to_string(&mut contents)?;
    let num = contents.parse()?;
    Ok(num)
}

#[derive(Debug, Fail)]
enum Error {
    #[fail(display = "{}", e)]
    IoFailed {
        #[fail(cause)]
        e: io::Error,
    },
    
    #[fail(display = "{}", e)]
    ParseIntFailed {
        #[fail(cause)]
        e: ParseIntError,
    },
}

impl From<io::Error> for Error {
    fn from(e: io::Error) -> Error {
        Error::IoFailed { e }
    }
}

impl From<ParseIntError> for Error {
    fn from(e: ParseIntError) -> Error {
        Error::ParseIntFailed { e }
    }
}

fn main() {
    let file = Path::new("number.txt");
    match do_io_things(&file) {
        Ok(num) => println!("the number is {}", num),
        Err(e) => println!("{}", e),
    }
}