Empty cases make rock crash

[nddrylliog]

If you have a match like this:

match foo {
  case bar: Baz =>
}

rock will fail with:

[OutOfBoundsException in ArrayList]: Trying to access an element at offset 0, but size is only 0!

[jussi-kalliokoski]

foo := 1;
match foo {
  case 1 =>
}

Builds and runs just fine. Not sure empty case is the problem. Btw, I have no idea what happens with that colon and class (: Baz) there, couldn't find documentation on that either?

$ rock --version
rock 0.9.6 codename loki, built on Wed Mar 13 22:57:47 2013

[nddrylliog]

@jussi-kalliokoski What happens with that colon and class is that the object is checked for its type, and cast to the appropriate target.

For example:

kill: func (entity: Entity) {
  match entity {
    case hero: Hero =>
      // I refuse to kill the hero!
      hero cheer()
    case enemy: Enemy =>
      enemy die()
  }
}

This is akin to Scala pattern matching, although much weaker/simpler.

What made my example blow up I think is that the match was used as a value (for example, as the return expression of a function.. or a variable decl.. or anything really).

So rock is looking for an expression in the case to assign to the temp value, and it fails.

Example:

a := match 1 {
  case 1 => // there's nothing there, blow up!
}

If it was correct, e.g.:

a := match Random randInt(1, 2) =>
  case 1 =>
    "blah"
  case 2 =>
    "blih"

Then it would compile down to something like this:

a: String
r := Random randInt(1, 2)
if (r == 1) {
  a = "blah"
} else if (r == 2) {
  a = "blih"
}

Except not really because of #615, but that's a separate issue :)

[jussi-kalliokoski]

Ahhh, ok, that makes sense, thanks. But not sure the example should even compile to anything, but the current behavior admittedly isn't desirable either. It would be good to get a descriptive error for this.

[nddrylliog]

Ah no the current example should err with 'no usable value in case inside a match used as expression' or some other less terrible error message. In any case it should definietly not crash rock.

[alexnask]

Will be on it tomorrow

[nddrylliog]

@shamanas Welcome back!

[alexnask]

@nddrylliog Happy to be here again! o/

[alexnask]

I can't seem to reproduce this on pacino (.9.7.x), I only get "Couldn't figure out type of match" error (which is tagged as a serious error that should be reported)

[nddrylliog]

Well.. then I don't know exactly what piece of code caused it, but in any case a check should be added when looking for a Scope's last element - if the Scope is empty => compile error.

[nddrylliog]

Complete test case:

Baz: class {}
foo := Baz new()

match foo {
  case bar: Baz =>
}

[nddrylliog]

Closed in 97x.