enum Mark {
    Circle { r: f64 }, Rect { w: f64, h: f64 },
    Label { text: Vec<u8> }, Dot,
}
fn main() {
    use std::io::{self, Write};
    let mut marks: Vec<Mark> = Vec::new();
    let mut mark_at: Vec<usize> = Vec::new();
    for mark in [Mark::Label { text: b"hello, goose".to_vec() },
                 Mark::Circle { r: 1.5 }, Mark::Dot,
                 Mark::Rect { w: 2.0, h: 3.0 }, Mark::Label { text: b"x".to_vec() }] {
        mark_at.push(marks.len()); marks.push(mark);
    }
    let mut out=io::stdout().lock();
    for i in [3, 0, 4, 1, 2] {
        match &marks[mark_at[i]] {
            Mark::Circle { r } => writeln!(&mut out,"{i}: circle {r}").unwrap(),
            Mark::Rect { w, h } => writeln!(&mut out,"{i}: rect {w} by {h}").unwrap(),
            Mark::Label { text } => {
                write!(&mut out,"{i}: label \"").unwrap();
                out.write_all(text).unwrap(); writeln!(&mut out,"\"").unwrap();
            }
            Mark::Dot => writeln!(&mut out,"{i}: dot").unwrap(),
        }
    }
}