playframework - How does Form populate `value` parameter in Scala Play framework without passing in? -

here code playing with

  def dologin = action { implicit request =>      val loginrequest = loginform.bindfromrequest.get    ok(s"username: '${loginrequest.username}', password: '${loginrequest.password}'")   }    def loginform = form(mapping("username" -> text, "password" -> text)       (loginrequest.apply)(loginrequest.unapply))    case class loginrequest(username:string, password:string) 

i confused on how .get able retrieve data, in source code

def get: t = value.get 

get retrieves value, value never populated in companion object

def apply[t](mapping: mapping[t]): form[t] = form(mapping, map.empty, nil, none)  case class form[t](mapping: mapping[t], data: map[string, string], errors: seq[formerror], value: option[t]) 

since passed in mapping

form(mapping("username" -> text, "password" -> text)       (loginrequest.apply)(loginrequest.unapply)) 

but when

print(loginform.bindfromrequest.get) 

it return loginrequest object, confused on value parameter populated, should none judging apply method in companion object of form