variable decleration

playground.rs

fn convert<S>(option: Option<S>) -> Option<String>
where
    S: Into<String>,
{
    match option {
        Some(string) => Some(string.into()),
        None => None
    }
}

fn is_ferris<S>(option: Option<S>) -> bool
where
    S: AsRef<str>,
{
    match option {
        Some(string) => string.as_ref() == "Ferris",
        None => false
    }
}

fn main() {
    let ferris: Option<String> = Some("Ferris").map(|s| s.into());
    let world = convert(Some("World"));

    let array: &[Option<String>] = &[None, ferris, world];

    for o in array.iter() {
        match o {
            Some(string) => println!("Hello {}", string),
            None => println!("PANIC!")
        }
        
    }
    

    let ferris: Option<&str> = Some("Ferris").map(|s| s.as_ref());
    let world: Option<String> = Some(String::from("World"));
    println!("Is it Ferris: none: {}, ferris: {}, world: {}",
        is_ferris(None::<&str>),
        is_ferris(ferris),
        is_ferris(world)
    );
}