What is the Scala equivalent to a Java builder pattern?

Question

In the work that I do on a day to day in Java, I use builders quite a lot for fluent interfaces, e.g.: new PizzaBuilder(Size.Large).onTopOf(Base.Cheesy).with(Ingredien

Answer 1

Case classes solve the problem as shown in previous answers, but the resulting api is difficult to use from java when You have scala collections in your objects. To provide a fluent api to java users try this:

case class SEEConfiguration(parameters : Set[Parameter],
                               plugins : Set[PlugIn])

case class Parameter(name: String, value:String)
case class PlugIn(id: String)

trait SEEConfigurationGrammar {

  def withParameter(name: String, value:String) : SEEConfigurationGrammar

  def withParameter(toAdd : Parameter) : SEEConfigurationGrammar

  def withPlugin(toAdd : PlugIn) : SEEConfigurationGrammar

  def build : SEEConfiguration

}

object SEEConfigurationBuilder {
  def empty : SEEConfigurationGrammar = SEEConfigurationBuilder(Set.empty,Set.empty)
}


case class SEEConfigurationBuilder(
                               parameters : Set[Parameter],
                               plugins : Set[PlugIn]
                               ) extends SEEConfigurationGrammar {
  val config : SEEConfiguration = SEEConfiguration(parameters,plugins)

  def withParameter(name: String, value:String) = withParameter(Parameter(name,value))

  def withParameter(toAdd : Parameter) = new SEEConfigurationBuilder(parameters + toAdd, plugins)

  def withPlugin(toAdd : PlugIn) = new SEEConfigurationBuilder(parameters , plugins + toAdd)

  def build = config

}

Then in java code the api is really easy to use

SEEConfigurationGrammar builder = SEEConfigurationBuilder.empty();
SEEConfiguration configuration = builder
    .withParameter(new Parameter("name","value"))
    .withParameter("directGivenName","Value")
    .withPlugin(new PlugIn("pluginid"))
    .build();