uppercase, lowercase, Unicode, chars and Rust

test.rs

fn main() {
    let y = "y̆";
    let mut chars = y.chars();
    assert_eq!(Some('y'), chars.next()); // not 'y̆'
    assert_eq!(Some('\u{0306}'), chars.next());
    // INTERESTING: chars is unicode compatible, it just gives you code points in between your graphemes
    for c in y.chars() {
        println!("{}", c.is_lowercase()); // true, false
    }

    assert!("y̆"
        .chars()
        .filter(|c| c.is_alphabetic())
        .all(|c| c.is_lowercase())); // true
    
    assert!(is_lowercase("京"));
}

/// it is better to identify the presence of uppercase
/// because scripts that don't have the concept of case
/// will return false on `char::is_lowercase`
/// (...but are not uppercase either!)
fn is_lowercase(s: &str) -> bool {
    !s.chars().any(|c| c.is_uppercase())
}