gistfile1.rs

use std::io::IoResult;

trait Shape {
    fn draw(&self, size: uint, buf: &mut Writer) -> IoResult<()>;
}

fn draw<T: Shape>(shape: T, size: uint) {
    match shape.draw(size, &mut std::io::stdio::stdout()) {
        Ok(_) => (),
        Err(e) => fail!(e),
    }
}

struct Triangle {
    ch: char,
}

struct Diamond {
    ch: char,
}

impl Shape for Triangle {
    fn draw(&self, size: uint, buf: &mut Writer) -> IoResult<()> {
        for i in range(1, size + 1) {
            for _ in range(0, i) {
                try!(write!(buf, "{}", self.ch));
            }
            try!(writeln!(buf, ""));
        }
        Ok(())
    }
}

impl Shape for Diamond {
    fn draw(&self, size: uint, buf: &mut Writer) -> IoResult<()> {
        let pad = size & 1;
        let radius = size / 2 + 1;
        for i in range(1, radius + pad).chain(range(1, radius).rev()) {
            for _ in range(1, radius - i) {
                try!(write!(buf, " "));
            }
            for _ in range(0, i * 2 - pad) {
                try!(write!(buf, "{}", self.ch));
            }
            try!(writeln!(buf, ""));
        }
        Ok(())
    }
}

fn main() {
    let t = Triangle { ch: '*' };
    let d = Diamond { ch: '#' };
    draw(t, 8);
    draw(d, 8);
}