とよぎぃ通信 vol.8 に登場するRustコード例

toyogy_vol8_rust_example.rs

fn main() {
    // Variable binding
    let a = 1; // immutable
    let mut b = 1; //mutable
    assert_eq!(b, 1);
    //    a = 2; // compile error
    b = 2;
    let c: i32 = 1; // i32 is 32 bit signed integer
    assert_eq!(a, c); // a == c
    assert_eq!(b, 2); // b == 2

    // Option type
    let some_i32: Option<i32> = Some(3);
    let none_i32: Option<i32> = None;
    assert_eq!(some_i32.unwrap(), 3);
    assert_eq!(none_i32.unwrap_or(1), 1);

    // Result type
    let ok_i32: Result<i32, &str> = Ok(3);
    let err_i32: Result<i32, &str> = Err("error");
    assert_eq!(ok_i32.unwrap(), 3);
    assert_eq!(err_i32.unwrap_or(1), 1);
    assert!(ok_i32.is_ok());
    assert!(err_i32.is_err());

    // if-let expression
    if let Some(x) = some_i32 {
        println!("{}", x);
    } else {
        println!("None");
    } // output: "3"
    if let Some(x) = none_i32 {
        println!("{}", x);
    } else {
        println!("None");
    } // output: "None"

    // match expression
    match some_i32 {
        Some(x) => println!("{}", x),
        None => println!("None"),
    } // output: "3"

    match ok_i32 {
        Ok(x) => println!("{}", x),
        Err(e) => println!("error info. is: {},", e),
    } // output: "3" 
    match err_i32 {
        Ok(x) => println!("{}", x),
        Err(e) => println!("{}", e),
    } // output: "error"

    // match expression (more complicated pattern)
    match some_i32 {
        Some(x @ 2...5) => println!("it is {}, it is in two to five", x),
        Some(_) => println!("it is other value"),
        None => println!("None"),
    }
}