filter numbers by named function

---

examples/vectors/filter-numbers-by-function/src/main.rs

fn positive(number: &&i32) -> bool {
    number.is_positive()
}

fn main() {
    println!("{}", positive(&&3));
    println!("{}", positive(&&-3));
    let numbers: Vec<i32> = vec![-7, 0, 1, 2, 22, 23];
    dbg!(&numbers);

    let positive_numbers: Vec<i32> = numbers.iter().filter(|number| number.is_positive()).cloned().collect();
    dbg!(&positive_numbers);

    let positive_numbers: Vec<i32> = numbers.iter().filter(positive).cloned().collect();
    dbg!(&positive_numbers);

}