How to get an Option’s value or set it if it’s empty?

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Looks to me like you want the get_or_insert_with() method. This executes a closure when the Option is None and uses the result as the new value:

fn get_name(&mut self) -> &String {
    self.name.get_or_insert_with(|| String::from("234"))
}

If you already have a value to insert, or creating the value isn’t expensive, you can also use the get_or_insert() method:

fn get_name(&mut self) -> &String {
    self.name.get_or_insert(String::from("234"))
}

You’ll also need to change your main() function to avoid the borrowing issue. An easy solution would be to derive Clone on your struct and then .clone() it in the call to println!():

fn main() {
    let mut app = App {
        name: None,
        age: 10,
    };

    println!("{:?} and name is {}", app.clone(), app.get_name())
}

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