use std::fs::File;
use std::io::Write;

struct Stuff {
    file: Option<File>,
}

impl Stuff {
    fn do_stuff(&mut self) {
        let file;
        let mut file2 = match self.file.as_ref() {
            Some(file) => file,
            None => {
                file = File::create("temp file").unwrap();
                &file
            }
        };

        writeln!(file2, "asdf").unwrap();
    }
}