What is the Option Type in Rust

Option in Rust represents a value that may or may not be there: It is optional.

Consider the following example where we have some configuration for our program. This configuration lets the user set their favorite color.

struct Config {
    favorite_color: Option<String>
}

fn main() {
    let config = Config {
        favorite_color: Some("pink")
    }
}

Now there are many reasons we might not have a value here yet. Maybe the user hasn't set a favorite color since it's their first time using the program. Maybe they don't even have a favorite color! So instead of using String as the type of favorite_color, we use Option<String>. This lets the user decided whether or not they want the program to know what their favorite color is.

struct Config {
    favorite_color: Option<String>
}

fn main() {
    let config = Config {
        favorite_color: None
    }
}

In the first example the user's favorite color was "pink", and in the second example the user doesn't have one. These differences are represented by Some(value) and None.