Java 20 / JDK 20: General Availability

Re:Java 20 / JDK 20: General Availability by jgon on Tuesday March 21, 2023 @06:58PM (#35253938)

I wanted to experiment with creating a "Rust-like" option and result type for Java and so figured that I would need records and pattern matching for this and I ran into exactly what you are talking about here with records and public constructors.

My solution was to create a sealed interface that permitted the None and Some records as the only classes to implement it. Those records are not available outside the package, while the interface is exposed. Using default methods in the interface I could expose a state "create()" method which would then instantiate the appropriate None or Some record. In this way you control the exposure of the construction of the specific record implementations of your interface.

You can then either interact with the option through the methods on the interface, .isOk(), .unwrap(), etc, etc, or with the upgraded pattern matching in switches with this release you could have something like

  switch(option) {
    case option when option.isNone() -> blah
    case option when option.isSome() -> foo

}

Its not as please as Rust matching directly on Some and None, but it gets you pretty close.

[ Parent | on HN ]

Re:Java 20 / JDK 20: General Availability by kaba0 on Wednesday March 22, 2023 @03:09AM (#35257781)

This is not really pattern matching, that’s just a regular old if-else.

https://news.ycombinator.com/item?id=35133670

This is absolutely possible in Java and the only less-than-ideal part is the generic type having to be specified in the None case (but a trivial method fixes that as well)

This can be used just like rust and similar languages:

  switch (option) {
    case Some(var x) -> println(x);
    case None -> // TODO
  }

Hell, you can just further pattern match inside Some, like `Some(Point(var x, var y))`

[ Parent | on HN ]