A `Result<T, E>` represents an operation that either succeeds with a value or fails with an error. It is commonly used as a function return type for fallible operations. section 4.6
Listing 4.15 Snippet of std::result::Result, from http://mng.bz/M97Q
pub enum Result<T, E> {
Ok(T),
Err(E),
}
The two variants encode success and failure, with separate types for the value and error. section 4.6
Use `?` to propagate an error immediately or continue with the successful value. When the error types differ, implement `From` to convert between them. section 4.6
fn read_file(name: &str) -> Result<String, Error> {
use std::fs::File;
use std::io::prelude::*;
let mut file = File::open(name)?; #1
let mut contents = String::new();
file.read_to_string(&mut contents)?; #2
Ok(contents)
}
This file-reading function propagates errors from both file opening and reading, then returns the contents as `Ok`. section 4.6
For crate APIs, return a crate-specific error type so callers can identify where an error originates. Fallible conversions use `TryFrom` and `TryInto`, which return `Result` rather than requiring a panic on failure. section 4.6 section 4.7.1
Handle I/O and other edge cases instead of bypassing them with `unwrap()`; testing should focus on logic, including conversions that can fail. section 6.4
