I'm currently learning Scala, and just discovered the way to create custom field getters/setters. I have a simple example working:
class Thing(private val a:Int){
override def toString = "Thing[" + a + "]"
private var _value = a
def value = _value
def value_= (newVal:Int) = _value = newVal
}
On the console I can do:
scala> var t = new Thing(2)
t: dylan.code.Thing = Thing[2]
scala> t.value
res1: Int = 2
scala> t.value = 3
scala> t.value
res2: Int = 3
Now I'm trying to bring this concept to a slightly more complicated example; I'll try to whittle the code down to what's relevant:
abstract class CellExpression[Type] extends Publisher[CellUpdateEvent[Type]] with Subscriber[CellUpdateEvent[Type], CellExpression[Type]]{
protected var cachedValue: Type = recalculateValue()
protected def recalculateValue(): Type
protected def changeValue(newValue: Type):Unit = {
val oldValue = value()
if(newValue != oldValue){
cachedValue = newValue
publish(new CellUpdateEvent(this, oldValue, newValue))
}
}
def value() = cachedValue
def notify(pub: CellExpression[Type], event: CellUpdateEvent[Type]) = changeValue(recalculateValue())
}
//....
class CellVariable[Type](private val initialValue:Type) extends CellExpression[Type]{
cachedValue = initialValue
protected def recalculateValue() = { cachedValue }
override def toString = "CellVariable[" + value + "]"
def value_= (newValue:Type) = {changeValue(newValue)}
}
As far as I can tell, I've done what I need to in order to be able to treate value
as a field via its getter and setter. But when I try it out in the console, I get:
scala> var i = new CellVariable(2)
i: dylan.code.CellVariable[Int] = CellVariable[2]
scala> i.value = 3
<console>:11: error: reassignment to val
i.value = 3
^
What have I done wrong, and how can I fix it?
I actually stumbled onto the solution.
The line where I declare my value function: def value() = cachedValue
is the culprit.
If I remove the parentheses to make the line def value = cachedValue
everything seems to work as I expected.
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