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Currently brewing in Scalactic master: bounded AnyVal types, including Pos (a positive Int)
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| scala> import org.scalactic.numbers._ | |
| import numbers._ | |
| // Pos is a type that ensures its "contained" value is a positive Int. I put "contained" | |
| // in scare quotes because Pos is an AnyVal, so it should only box when an Int would box. | |
| // You can create them directly with positive integer literals, like this: | |
| scala> Pos(3) | |
| res0: org.scalactic.numbers.Pos = Pos(3) | |
| // If you pass an Int variable, or a non-positive Int literal, to this factory method, it | |
| // won't compile: | |
| scala> Pos(-3) | |
| <console>:20: error: Pos.apply can only be invoked on a positive (i > 0) integer literal, like Pos(42). Please | |
| use Pos.from instead. | |
| Pos(-3) | |
| ^ | |
| scala> val x = 3 | |
| x: Int = 3 | |
| scala> Pos(x) | |
| <console>:21: error: Pos.apply can only be invoked on a positive (i > 0) integer literal, like Pos(42). Please | |
| use Pos.from instead. | |
| Pos(x) | |
| ^ | |
| // The Pos.from factory will work on any value of type Int, but gives back an Option[Pos] | |
| scala> Pos.from(3) | |
| res3: Option[org.scalactic.numbers.Pos] = Some(Pos(3)) | |
| scala> Pos.from(-3) | |
| res4: Option[org.scalactic.numbers.Pos] = None | |
| scala> Pos.from(x) | |
| res5: Option[org.scalactic.numbers.Pos] = Some(Pos(3)) | |
| // You can use a Pos where an Int is required | |
| scala> def takesInt(i: Int): Int = i + 1 | |
| takesInt: (i: Int)Int | |
| scala> takesInt(Pos(3)) | |
| res6: Int = 4 | |
| // You can also use a valid Int literal where a Pos is required. | |
| scala> def takesPos(pos: Pos): Int = pos + 1 | |
| takesPos: (pos: org.scalactic.numbers.Pos)Int | |
| scala> takesPos(Pos(3)) | |
| res7: Int = 4 | |
| scala> takesPos(3) | |
| res8: Int = 4 | |
| // As with the Pos apply factory, you'll get a compiler error if you try to use | |
| // an Int variable or non-positive Int literal where an Int is required. | |
| scala> takesPos(-3) | |
| <console>:21: error: Pos.apply can only be invoked on a positive (i > 0) integer literal, like Pos(42). Please | |
| use Pos.from instead. | |
| takesPos(-3) | |
| ^ | |
| scala> takesPos(x) | |
| <console>:22: error: Pos.apply can only be invoked on a positive (i > 0) integer literal, like Pos(42). Please | |
| use Pos.from instead. | |
| takesPos(x) | |
| ^ | |
| // You'll be able to use Pos with any operator you can use on Int, but if there's any chance | |
| // you could end up with a negative number, you'll get an Int as the result: | |
| scala> Pos(3) + Pos(4) | |
| res11: Int = 7 | |
| // Here's an example where the + operator yields a negative Int: | |
| scala> Pos(3) + Pos(Int.MaxValue) | |
| res12: Int = -2147483646 |
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