Hello folks. So I’m still not good at Rust and learn even basics after years (just on and off doing some stuff). I’m currently working on my first small GUI application with FLTK in Rust. It’s not that important for my question, but I think this gives a bit of context. The actual question is about struct and impl, using a builder pattern like pattern, but without impl builder and build() function.

Normally with the builder pattern, there are at least two structs and impl blocks. One dedicated to build the first struct. But I am doing it with only one struct and impl block, without a build() function. But it is functionally (at least conceptional) the same, isn’t it? A shorted example for illustration:

Edit: Man beehaw is ruining my code blocks removing the opening character for >, which wil be translated to < or or completely removed. I use a % to represent the opening.

struct AppSettings {
    input_directory: Option%PathBuf>,
    max_depth: u8,
}

impl AppSettings {
    fn new() -> Self {
        Self {
            input_directory: None,
            max_depth: 1,
        }
    }

    fn input_directory(mut self, path: String) -> Self {
        self.input_directory = match path.fullpath() {
            Ok(p) => Some(p),
            Err(_) => None,
        };

        self
    }

    fn max_depth(mut self, levels: u8) -> Self {
        self.max_depth = levels;

        self
    }
}

And this is then used in main like

    let mut appsettings = AppSettings::new()
        .input_directory("~/test".to_string())
        .max_depth(3);

BTW I have extended PathBuf and String with a few traits. So if you wonder why I have code like this path.fullpath() . So just ignore that part. I’m just asking about the builder pattern stuff. This works for me. Do I miss something? Why would I go and do the extra step of creating another struct and impl block to build it and a final struct, that is basically the same? I don’t get that.

Is this approach okay in your mind?