Rémi Forax's Blog

February 2007 Archives

Closure Litteral and Method Reference

Recently, Stephen Colebourne and Stefan Schulz post another closure like proposal, yes, yet another one.

They propose another syntax for describing a closure which, in my opinion, is more a simpler way to declare an inner-class.
I am not a big fan of this proposal, i definitively prefer the closure syntax decribed by Neal Gafter.
But there is something that i like in their proposal, the fact that you can create invocable method references.

Invocable Method Reference

We need a way to easily create a reference to a method, an object that allow to call a method. Currently a method is not an Object and if you want something like that you have to use reflection (java.lang.reflect.Method) which is not type-safe, uses lot of checked exceptions and performs primitive boxing and array boxing.

So having a way to create a method reference is a good think. But unlike Stephen and Stefan, i don't think that a method reference is a java.lang.reflect.Method correctly typed by the compiler but instead a java.function object (a closure) of Neal.
In my opinion method reference is a kind of closure litteral, so this code snippet:

  public void init() {
    JButton button = ...;
    button.addActionListener(this#handleAction(ActionEvent));
  }
  public void handleAction(ActionEvent ev) {
    // handle event
  }

is a short syntax for:

  public void init() {
    JButton button = ...;
    button.addActionListener({ActionEvent e=>
      handleAction(e);
    });
  }
  public void handleAction(ActionEvent ev) {
    // handle event
  }

Because a method reference is a closure litteral, the type of a method reference is a function type.

 {ActionEvent=>void} handle = this#handleAction(ActionEvent);

I think that using # is a good idea. Perhaps because it's the syntax i choose to use to create property litteral (property reference) in my next property proposal that i will post in few days.

Cheers, Rémi

Meet me at FOSDEM

If you want to talk about:

1. Why the JLS doesn't allow array of parametrized type.
2. Kitchen Sink Language.
3. Property syntax.
4. Why beers are so great in Belgium ?

I will be saturday and sunday at FOSDEM.

Rémi

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