Lazy way to initialize a class without having multiple constructors (only works with mutable vars)

main.swift

class Demo {
  var foo: String? = nil
  var bar: String? = nil
  
  init(block: (Demo) -> Void) {
    block(self)
  }
}

Demo {
  $0.foo = "bar"
}

Demo {
  $0.bar = "foo"
}

Demo {
  $0.foo = "bar"
  $0.bar = "foo"
}