CODEWITHSUNDEEP
scala
Tilo
Tilo

Reputation: 3325

Implicit conversion of function type

I'm going through this JavaFX tutorial, using Scala as the implementation language, and ran into an issue with my implicit conversion not being picked up:

class HelloApplication extends Application {
  import HelloApplication._

  override def start(stage: Stage) {
    stage.setTitle("Hello World!")
    val btn = new Button()
    btn.setText("Say 'Hello World'")
    btn.setOnAction(function2EventHandler(buttonPressed))

    val root = new StackPane()
    root.getChildren.add(btn)
    stage.setScene(new Scene(root, 300, 250))
    stage.show()
  }

  def buttonPressed(ev: ActionEvent) {
    println("Hello World!")
  }
}

object HelloApplication {
  implicit def function2EventHandler[A <: Event](f: A => Unit): EventHandler[A] = 
    new EventHandler[A] {
      override def handle(t: A) = f(t)
    }
}

When I change this line

btn.setOnAction(function2EventHandler(buttonPressed))

to

btn.setOnAction(buttonPressed)

I'm getting a compilation error. Can you point me to what I'm doing wrong?

I'm using the JavaFX that ships with JDK 7 and Scala 2.11.4.

Upvotes: 1

Views: 82

Answers (1)

Yuriy
Yuriy

Reputation: 2769

First what I see, that: buttonPressed is an expression of method type NOT function type

def buttonPressed(ev: ActionEvent) {
    println("Hello World!")
}

I think you need to use eta expansion (§6.26.5 Eta Expansion ScalaReference) before implicit conversion:

btn.setOnAction(buttonPressed _)

Upvotes: 5

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