Keep the JVM, dump the rest ([thoughts on] Scala+Play+MongoDB)

http://blog.ometer.com/2011/03/29/keep-the-jvm-dump-the-rest/

by mccutchen • 15 years ago

16 4 15 years ago

blog.ometer.com

mccutchen• 15 years ago

Like the author, I'd be interested in hearing about better ways to handle Scala's `Option` type.

dlwh• 15 years ago

Option can occasionally be a pain to handle, I admit. But typically it works really well for me.

The standard Haskell-ish approach is to use for-comprehensions:

val maybeWebpage = for(foo <- maybeFoo) yield { // do things with foo, yielding some resulting webpage snippet or whatever }

As he points out, this can cause Options to propagate, but it does allow you to defer dealing with the exception until later. You can reasonably argue that it leads to better modularity, since you can dump all of your error handling in the same function, and different callers can decide how they want to process errors.

Nevertheless, the OP wants a getOrThrow method (which he could of course add via implicits), but you can also just use getOrElse, which usually returns some other expression in the case of None, but since throw is just an expression in Scala, you can use it there:

scala> val foo = Some("foo").getOrElse(throw new Exception("whatever")) foo: java.lang.String = foo

scala> val foo = None.getOrElse(throw new Exception("whatever")) java.lang.Exception: whatever at $anonfun$1.apply(<console>:5) at $anonfun$1.apply(<console>:5) at scala.Option.getOrElse(Option.scala:104) at .<init>(<console>:5)

kikibobo69• 15 years ago

One nice trick with Option, is how you can replace null checks for common operations. For example, consider the difference between:

InputStream i = ...

if (i != null) { i.write(...) }

vs.

val i: Option[InputStream] = ..

i.map(_.write(...))

Simple, safe, works really well.

evangineer• 15 years ago

If I was doing JVM based development, I'd probably be using Mirah instead of Scala & CouchDB rather than MongoDB.

Keep the JVM, dump the rest ([thoughts on] Scala+Play+MongoDB)

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