simple.rs

pub struct Inserter;

pub struct Controller {
  pub inserter : Inserter,
  pub conn: Connection
}

pub struct ConnectedInserter<'a> {
    conn: &'a SqliteConnection, 
}

impl ConnectedInserter {
  pub fn insert_smth() {}
}

impl Inserter {
    pub fn new() -> Inserter {
        Inserter {}
    }

    pub fn with(&self, connect : &Connection ) -> ConnectedInserter {
        ConnectedInserter {
            conn: connect  
        }
    }
}

impl Controller {
  pub fn use() {
    self.inserter.with(self.conn).insert_something();
  }
}

fn main() {
  let control = Controller { inserter : Inserter {}, conn : Connection::new() };
  control.use();
}