Angular Style Filters in Scala/Twirl

angular-filters.scala

// ---- Presenter Pattern ----

// presenters.scala
object presenters {
  implicit class StringPresenter(s: String) {
    def reverse = Html(s.reverse)
  }
  
  implicit DateTimePresenter(dt: DateTime){
    def format(f: String) = DateTimeFormat.forPattern(f).print(dt)
  }
}


// index.scala.html
@import presenters._
        
@main {
  <h1>@message.reverse</h1>
  <h3>@event.start.format("YYYY-MM-dd")</h3>
}


// -------------------------------------------------------


// ---- Filter Pattern ----

// filters.scala
object filters {

  // --- Setup (once for all filters) ---

  type HtmlFilter[A] = (A) => Html

  implicit class Filtererer[A](a: A) {
    def |||(filter: HtmlFilter[A]): Html = filter(a)
  }

  // --- Filter Examples ---

  val reverse = new HtmlFilter[String] {
    def apply(s: String) = Html(s.reverse)
  }

  def format(f: String) = new HtmlFilter[DDateTime] {
    def apply(date: DateTime) = Html(DateTimeFormatter.forPattern(f).print(date))
  }
}


// index.scala.html
@import filters._

@main {
  <h1>@{ message ||| reverse }</h1>
  <span>@{ event.start ||| format("YYYY-MM-dd") }</span>
}

If you're wondering why ||| instead of just |, it's because Twirl has | already setup to be a boolean comparison operator.