strings wrapped up in Option

playground.rs

use rand; // 0.7.3
use rand::Rng;

fn make_a_string_with_optional<S>(option: Option<S>) -> String
where
    S: AsRef<str>,
{
    let mut s = String::from("Hello");
    if let Some(string) = option {
        s.push_str(" ");
        s.push_str(string.as_ref());
    }

    let mut rng = rand::thread_rng();
    let r = rng.gen_range(0, 100);
    for _ in 0..r {
        s.push_str("!");
    }
    s
}

fn main() {
    let world_slice = "World";
    let world_string = String::from(world_slice);

    let none = make_a_string_with_optional(None::<&str>);
    let some_literal = make_a_string_with_optional(Some("Ferris"));
    let some_slice = make_a_string_with_optional(Some(world_slice));
    let some_string = make_a_string_with_optional(Some(String::from(world_slice)));
    let some_ref_string = make_a_string_with_optional(Some(&world_string));

    let array: &[String] = &[none, some_literal, some_slice, some_string, some_ref_string];

    for s in array.iter() {
        println!("len: {}, string: {}", s.len(), s)
    }
}