Rust Error Handling

enum Result<T, E> { # built-in enum
    Ok(T), # success with value
    Err(E), # error with value
}

use std::fs::File;
let f = File::open("file.txt"); # returns Result
match f {
    Ok(file) => println!("Success"),
    Err(error) => println!("Error: {}"{}, error),
}

let f = File::open("file.txt").unwrap(); # panic on error
let f = File::open("file.txt").expect("Failed to open"); # custom panic message

fn read_file() -> Result<String, std::io::Error> {
    let mut f = File::open("file.txt")?; # return error if Err
    let mut contents = String::new();
    f.read_to_string(&mut contents)?;
    Ok(contents) # return Ok variant
}

let some = Some(5); # has value
let none: Option<i32> = None; # no value
let x = some.unwrap_or(0); # use default if None