#[derive(Debug)]
struct St {
  a: String,
  b: i64
}

impl St {
  pub fn new() -> Self {
    Self {
      a: "a".to_string(),
      b: 4
    }
  }
  pub fn a(&mut self, a: String) -> &mut Self {
    self.a = a;
    self
  }
  pub fn b(&mut self, b: i64) -> &mut Self {
    self.b = b;
    self
  }
}

fn main() {
  println!("{:?}", St::new().b(23))
}