Trying to implement a Circular Enumeration in Scala - scala

Question

Below is the trait that I would like to use
trait CircularEnumeration extends Enumeration {
class CircularVal extends Val {
def next(): Value = {
apply((id + 1) % values.size)
}
}
protected override final def Value: CircularVal = new CircularVal;
///////////////////////////////////////////////////////////////////////////
def nextValue(value: Value) = {
//first way
val nextIndex = values.toSeq.indexOf(value) + 1;
val value_nomath = if (nextIndex >= values.size) {
values.toSeq(0);
}
else {
values.toSeq(nextIndex);
}
//second way
val value_withmath = this((value.id + 1) % values.size);
assert(value_nomath == value_withmath);
value_withmath;
}
}
You can see that I already have tried two ways, and both have failed.
In the first the usage would be something like this:
MyEnumeration(index).next
and this would return me the next value of this enumeration
In the second the usage would be like that:
MyEnumeration.nextValue(MyEnumeration(index))
and once again this would return the next value
but in both occasions I have issues of which type is which. Because inside the trait the Value is actually CircularEnumeration.Value while inside the class which has this trait tha Value is MyEnumeration.Value
Any ideas?

Answer 1

I believe I can get it to work with the following changes - modify the return type of nextValue:
def nextValue(value: Value): CircularEnumeration.this.Value = {
and the last line (returned value) to:
value_withmath.asInstanceOf[CircularEnumeration.this.Value]
Then, defining MyEnumeration as:
scala> object MyEnumeration extends CircularEnumeration {
| type MyEnumeration = Value
| val Zero, One, Two, Three, Four = Value
| }
defined module MyEnumeration
we get:
scala> MyEnumeration.nextValue(MyEnumeration(3))
res0: MyEnumeration.Value = Four
scala> MyEnumeration.nextValue(MyEnumeration(4))
res1: MyEnumeration.Value = Zero