Composite UI without boilerplate using Play 2

Application.scala

object Application extends Controller {
  
  val index = Action { implicit request =>
    Ok(views.html.index())
  }
  
  val show = Action { implicit request =>
    Ok(views.html.show("42"))
  }
  
  implicit def user(implicit session: Session): Option[User] = {
    for (name <- session.get("username")) yield User(name)
  }
}

ApplicationBoilerplate.scala

object Application extends Controller {
  
  val index = Action { implicit request =>
    Ok(views.html.index(user(session)))
  }
  
  val show = Action { implicit request =>
    Ok(views.html.show(user(session), "42"))
  }
  
  def user(session: Session): Option[User] = {
    for (name <- session.get("username")) yield User(name)
  }
}

show-boilerplate.html

@(user: Option[User], message: String)

@main(user) {
  <h1>@message</h1>
}

show.html

@(message: String)(implicit user: Option[User])

@main {
  <h1>@message</h1>
}

Users.scala

trait Users {
  implicit def user(implicit session: Session): Option[User] = {
    for (name <- session.get("username")) yield User(name)
  }
}

object Application extends Controller with Users {
  
  val index = Action { implicit request =>
    Ok(views.html.index())
  }
  
  val show = Action { implicit request =>
    Ok(views.html.show("42"))
  }
}