Simple implicit conversions in Scala

Question

I'm pretty new to scala and I really love it so far but I'm stuck with a really weird problem. I wanted to try implicit conversions by implementing D&D-style dice expressions. i.e. 2d12 "throw two twelve-sided dice" ... you know what I mean.

From what I understand scala should be able to compile this

(1 d 6).roll

and probably even this

1d6 + 2 - 1d30

but I get a "value d is not a member of int" compile error in my specs test.

package meh.toast import scala.util.Random object Dice { class DiceSymbol(val amount:Int) { def d(sides:Int):Dice = new Dice(amount, sides) } implicit def int2DiceSymbol(amount:Int) = new DiceSymbol(amount) implicit def dice2Int(d:Dice) = d.roll private val rnd = new Random() protected def throwDice(sides:Int) = rnd.nextInt(sides) + 1 } class Dice(amount:Int, sides:Int) { def roll:Int = (1 to amount) map { _ => Dice.throwDice(sides)} sum }

I'm really stuck. It would be awesome if you could help, it's probably something really simple.

Thanks in advance

aaand I already fixed it myself ... I didn't import all the right packages .... for this Example to work you've got to import not only the packages meh.toast._ but also meh.toast.Dice._ from where you're using it. — ParkL
– ParkL, Commented Apr 10, 2012 at 23:50
and I found out one more thing (for me and the other scala noobs) ... 1 d 6 must be <= 6 works fine but 1d6 doesn't. That is because 1d would convert the int literal to a double and the compiler doesn't know what to make of the 6. So in real life "d" wouldn't be a very good choice for an operator name. "!" works great! can do 1!6 +2 — ParkL
– ParkL, Commented Apr 11, 2012 at 0:03
Just be careful: The ! is already used as the operator for sending a message to a Scala actor. I made good experience with first making the framework work without a DSL (as in, Die(1, 6)), and add the pimp DSL later, as a refinement. — Madoc
– Madoc, Commented Apr 11, 2012 at 12:30
That's true! And there may be even another implicit conversion with the ! defined leading to weird results if I get that right. I don't think an integer literal can also be an actor but I might be wrong. But as I said, I was only trying here :) I used ! only because it was 2:30 AM and it was the first that came to my mind ;) Thank you guys very much! — ParkL
– ParkL, Commented Apr 11, 2012 at 15:09

dhg · Accepted Answer · 2012-04-10 23:52:46Z

You're really close: but you have to make sure the implicit functions from the Dice object are in scope when you try to use them:

 scala> import Dice._ import Dice._ scala> (1 d 6).roll res12: Int = 2

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