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But without a pattern matching system, optional is still half of what it is in, say, Scala.



Why would you ever pattern match on Option[T] in Scala? In all my code, I do either:

    optionalF.map( _.whatever ).getOrElse(fallback)
or perhaps

    (optionalF <+> optionalFallback).getOrElse(finalFallback)
For those unfamiliar with <+>, see here: http://www.chrisstucchio.com/blog/2014/handle_failure_with_p...


I think that's a pretty extreme position. First, it will run a lot slower than the pattern matching alternative:

    optional match {
      case Some(x) => whatever(x)
      case None    => fallback
    }
Second, I find the pattern matching code much clearer. Sure, it's also longer, but clarity trumps everything.


map / getOrElse is standard in all the Scala code I've seen. Abstracting over the monad is also a pretty big win that has made some big refactorings painless for me. Pattern matching is really only used by beginners IME.


Well, then maybe the beginners do it right? You have not argued against my two points: It's much slower, and less clear.


Clarity comes from familiarity. It's not an objective measure.

The speed benefit is well known, as is the corollary, premature optimisation. I expect checking for null is even faster if speed is the main concern. It's an engineering tradeoff, just like making the abstraction to a monad (or monad plus). In the normal course of events I'm more concerned about flexibility than performance and would prefer the abstraction.


Isn't map/flatMap and orElse enough, if only for Optional?


It's not enough for compactly expressing imperative logic. In Scala:

  resultOption match {
    case Some(x) => println(x)
    case None => println("error")
  }
Without pattern match:

  if (resultOption.isDefined) {
    println(resultOption.get)
  } else {
    println("Error")
  }
The .get is the problem.


There are several ways of doing it concisely with the Java Optional

  import java.util.Optional;

  public class Scratch {
      public static void main(String... args) {
          Optional<String> foo = Optional.of("foo");
          Optional<String> bar = Optional.empty();

          System.out.println(foo.orElse("Error"));
          System.out.println(bar.orElse("Error"));

          foo.map(Print::print).orElseGet(() -> Print.print("Error"));
          bar.map(Print::print).orElseGet(() -> Print.print("Error"));

          foo.ifPresent(Print::print);

      }

      static class Print {
          public static <T> T print(T val) {
              System.out.println(val);
              return val;
          }
      }
  }




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