Rust for C-Programmers

14.7 Practical Examples

14.7.1 Handling Missing Data

Scenario: Parsing user input that may or may not contain valid integers.

use std::io;
fn parse_number(input: &str) -> Option<i32> {
    input.trim().parse::<i32>().ok()
}
fn main() {
    let inputs = vec!["42", "   ", "100", "abc"];
    for input in inputs {
        match parse_number(input) {
            Some(num) => println!("Parsed number: {}", num),
            None => println!("Invalid input: '{}'", input),
        }
    }
}

Output:

Parsed number: 42
Invalid input: '   '
Parsed number: 100
Invalid input: 'abc'

14.7.2 Implementing Safe APIs with Option

Scenario: Designing a function that retrieves configuration settings, which may or may not be set.

struct Config {
    database_url: Option<String>,
    port: Option<u16>,
}
impl Config {
    fn new() -> Self {
        Config {
            database_url: None,
            port: Some(8080),
        }
    }
    fn get_database_url(&self) -> Option<&String> {
        self.database_url.as_ref()
    }
    fn get_port(&self) -> Option<u16> {
        self.port
    }
}
fn main() {
    let config = Config::new();
    match config.get_database_url() {
        Some(url) => println!("Database URL: {}", url),
        None => println!("Database URL not set"),
    }
    match config.get_port() {
        Some(port) => println!("Server running on port: {}", port),
        None => println!("Port not set, using default"),
    }
}

Output:

Database URL not set
Server running on port: 8080