I understand that I can write
myArray(index) = newValue
to update an array. However, I don't understand how this works internally. I learned from another question here that = is usually not a method call in Scala. I also understand that the brackets are shorthand for calling the apply() method on an object, so I assume myArray(index) means myArray.apply(index).
But how does it work to assign a value to something that has just been returned from a method call?
You are correct that
myArray(index)
is syntactic sugar for
myArray.apply(index)
However, adding an assignment with the = operator completely changes the meaning:
myArray(index) = newValue
is a special syntax for the update method:
myArray.update(index, newValue)
This does not only apply for Arrays; you can make use of it on your own. In fact, many classes in the Scala Collections Framework make use of this syntactic sugar. For example, the scala.collection.mutable.Map#update(A,B) can also do this.
class MyClass(var i: Int)
{
def update(i: Int, j: Int) = { this.i = i + j }
}
var my = new MyClass(1)
my(1) = 2
println(my.i) // prints 3
