[tibordp]

That's a good point and also one of the things I kinda like about Alumina. You can do thing like this and the file will only be closed at the end of the function rather than the end of the if block.

    let stream: &dyn Writable<Self> = if output_filename.is_some() {
        let file = File::create(output_filename.unwrap())?
        defer file.close();

        file
    } else {
        &StdioStream::stdout()
    };