slice.md

fn main() {
    let arr = [1, 2, 3];
    let s1: &[i32] = &arr[0..2];

    let s2: &str = "hello, world";
}

fn main() {
    let arr: [char; 3] = ['中', '国', '人'];

    let slice = &arr[..2];

    // TIPS: slice( reference ) IS NOT an array, because if it is, then `assert!` will passed: each of the two UTF-8 chars '中' and '国'  occupies 4 bytes, 2 * 4 = 8
    assert!(std::mem::size_of_val(&slice) == 16);
}

fn main() {
    let arr: [i32; 5] = [1, 2, 3, 4, 5];
    let slice: &[i32] = &arr[1..4];
    assert_eq!(slice, &[2, 3, 4]);
}

fn main() {
    let s = String::from("hello");

    let slice1 = &s[0..2];
    let slice2 = &s[..2];

    assert_eq!(slice1, slice2);
}

fn main() {
    let s = "你好，世界";
    let slice = &s[0..3];

    assert!(slice == "你");
}

fn main() {
    let mut s = String::from("hello world");

    // here, &s is `&String` type, but `first_letter` needs a `&str` type.
    // it works because `&String` can be implicitly converted to `&str, If you want know more ,this is called `Deref` 
    let letter = first_letter(&s);

    println!("the first letter is: {}", letter);

    s.clear();
}

fn first_letter(s: &str) -> &str {
    &s[..1]
}