Unsigned variable using scala value classes

Question

Is there a neat way to create an unsigned variable using scala value classes?

case class Size(val size: Int) extends AnyVal {
 ....
   }

do you want something like this: `case class Size(size: Int) {def unsigned = if(size < 0) -size else size}; Size(-1).unsigned // 1` — Samar, Aug 30 '16 at 08:54
I need it more in a way to have an error if size < 0 , i did it like this but i get the error : this statement is not allowed in value class. `case class Size(val size: Long) extends AnyVal { if (size < 0) throw new IllegalArgumentException; def +(s: Size): Size =Size(size + s.size) }` — EY.Mohamed, Aug 30 '16 at 09:41
You are defining a "value class" and [value classes](http://docs.scala-lang.org/overviews/core/value-classes.html) don't allow any other operation except method definitions inside them. They also do not provide a constructor where you can validate the argument on instantiation. There are some work arounds: http://stackoverflow.com/questions/33136558/validations-in-value-classes — Samar, Aug 30 '16 at 10:55

score 0 · Answer 1 · answered Aug 30 '16 at 12:20

These facts may help you understand you question. (For better explanation, assume all numbers are 4-bits, unsigned ranges from [0, 15], signed ranges from [-8, 7])

In 2's complement, some number is same like -5 and 11 and 27 and so on, here the SAME not only means their representations are same, but also their operations:
```
-5 + 10 = 5
11 + 10 = 5
```
What's the difference between (un)signed and 2's complement ? (un)signed number should handle overflow, bu 2's complement doesn't.
```
 7 + 1 = throw OverflowException
-8 - 1 = throw OverflowException
```
The number of jvm is neither signed nor unsigned, it's 2's complement. jvm does not throw any overflow when triggered, so they are 2's complement, not (un)signed numbers.

What's the difference between signed and unsigned ?

They overflow under different condition:

             Signed           Unsigned
     7 + 1  overflow             8
 -8(7) - 1  underflow            6
     0 - 1     -1            underflow
-1(15) + 1      0            overflow

They are printed different.

These facts apply almost all programming languages.

Back to your question, since you don't handle overflow, the only thing you need to do is print it differently.

case class Size(val size: Int) extends AnyVal {
  override def toString = if (size < 0) ...
}

Unsigned variable using scala value classes

1 Answers1