Rust Error Handling Pattern

1use std::fs::File;
2use std::io::{self, Read};
3 
4#[derive(Debug)]
5enum AppError {
6    Io(io::Error),
7    Parse(std::num::ParseIntError),
8    Custom(String),
9}
10 
11impl From<io::Error> for AppError {
12    fn from(err: io::Error) -> Self {
13        AppError::Io(err)
14    }
15}
16 
17impl From<std::num::ParseIntError> for AppError {
18    fn from(err: std::num::ParseIntError) -> Self {
19        AppError::Parse(err)
20    }
21}
22 
23fn read_number_from_file(path: &str) -> Result<i32, AppError> {
24    let mut file = File::open(path)?;
25    let mut contents = String::new();
26    file.read_to_string(&mut contents)?;
27    let number: i32 = contents.trim().parse()?;
28    Ok(number)
29}
30 
31fn main() {
32    match read_number_from_file("number.txt") {
33        Ok(n) => println!("Number: {}", n),
34        Err(e) => eprintln!("Error: {:?}", e),
35    }
36}