Flash stuff, in Play.

SomeController.scala

object SomeController extends Controller {
  def signup = Action(parse.urlFormEncoded) { implicit request =>
    signupForm.bindFromRequest.fold(

      { form =>        // failure; repost

        BadRequest(views.html.register.signup(form))
      },

      { newUser =>     // success; create user and send confirmation

        val token = RandUtil.generateUniqueToken(newUser.email)
        val user = newUser.toUser.copy(confirmationToken = Some(token))

        User.create(user).fold(
          { error =>

            // Can't use "flashing" here, because the template will already
            // have been rendered by the time Ok is called. Instead, create
            // our own flash object and pass it to the template.
            //
            // This COULD be done with an implicit parameter, but using an
            // implicit parameter leads to less obvious code. Here's how,
            // though:
            //
            //     implicit val flash = Flash(Map(...))
            //     Ok(views.html.admin.edituser(...))
            val flash = Flash(Map("error" -> error))
            val filledForm = signupForm.fill(newUser)
            Ok(views.html.register.signup(filledForm)(flash))
          },

          { user =>

            sendConfirmationEmail(user, request)
            Redirect(routes.Register.postSignUp(token))
          }
        )
      }
    )
  }
}