My Struggles with Rust(compileandrun.com)

  foo().pop().expected("foo length >= 1");

   x + x + x + x

   4x

    * Use unwrap/expect when you don't care.
    * Use `try!`/`?` with Box<Error> in simple CLI applications.
    * Use `try!`/`?` with a custom error type and From impls in libraries.
    * Use combinators (e.g., map_err) when you need more explicit control.

    use std::error::Error;
    use std::fs::File;
    use std::io::{self, Read};

    fn main() {
        match example_explicit() {
            Ok(data) => println!("{}", data),
            Err(err) => println!("{}", err),
        }
    }

    fn example_explicit() -> Result<String, Box<Error>> {
        let file = match File::open("/foo/bar/baz") {
            Ok(file) => file,
            Err(err) => return Err(From::from(err)),
        };
        let mut rdr = io::BufReader::new(file);

        let mut data = String::new();
        if let Err(err) = rdr.read_to_string(&mut data) {
            return Err(From::from(err));
        }
        Ok(data)
    }

    use std::error::Error;
    use std::fs::File;
    use std::io::{self, Read};
    
    fn main() {
        match example_sugar() {
            Ok(data) => println!("{}", data),
            Err(err) => println!("{}", err),
        }
    }
    
    fn example_sugar() -> Result<String, Box<Error>> {
        let file = File::open("/foo/bar/baz")?;
        let mut rdr = io::BufReader::new(file);
        
        let mut data = String::new();
        rdr.read_to_string(&mut data)?;
        Ok(data)
    }

  let foo: Bar = ... ;

  fn foo() -> Bar { ... }