struct Seq {
    start: i32,
    end: i32,
}

impl Seq {
    pub fn new(start: i32, end: i32) -> Self {
        Self { start, end, }
    }
}

impl Iterator for Seq {
    type Item = i32;

    fn next(&mut self) -> Option<i32> {
        if self.start < self.end {
            let a = self.start;
            self.start += 1;
            Some(a)
        } else {
            None
        }
    }
}

fn main() {
    test_001();
    test_002();
    test_003();
    test_004();
}

// -> 10 11 12 13 14
fn test_001() {
    println!("## test001");
    let seq = Seq::new(10, 15);
    print!("->");
    for a in seq {
        print!(" {}", a);
    }
    println!();
}

// -> 10 11 12 13 14
fn test_002() {
    println!("## test002");
    let mut seq = Seq::new(10, 15);
    print!("->");
    while let Some(a) = seq.next() {
        print!(" {}", a);
    }
    println!();
}

// -> 10 11 12
fn test_003() {
    println!("## test003");
    let mut seq = Seq::new(10, 15).take(3);
    print!("->");
    while let Some(a) = seq.next() {
        print!(" {}", a);
    }
    println!();
}

// -> 10
// -> 10 11 12 13 14
fn test_004() {
    println!("## test004");
    let mut seq = Seq::new(10, 15).peekable();
    println!("-> {}", seq.peek().unwrap());
    print!("->");
    while let Some(a) = seq.next() {
        print!(" {}", a);
    }
    println!();
}