Creating empty scala mutable sequence and adding to it - scala

Question

I am trying to have to create an mutable sequence and then add to that sequence.
import scala.collection.mutable.Seq
// my case class
case class Apple(id: Int, color: String)
var sequence : Seq[Apple] = Seq.empty
for(a<-1 to 4) {
sequence :+ Apple(a, "green")
println("$$$$")
}
print(sequence)
However it's just empty.
result
$$$$
$$$$
$$$$
ArrayBuffer()defined class Apple
import scala.collection.mutable.Seq
sequence: scala.collection.mutable.Seq[Apple] = ArrayBuffer()
I tried to use ListBuffer but its just empty
var y = new scala.collection.mutable.ListBuffer[ Apple]
for(a<-1 to 4) {
y :+ Apple(a, "green")
println("$$$$")
}
y.size
Am I using the wrong structure to add my Apple to? I eventually want to create a DF from my list of Apples
Update
When I was using ListBuffer I forgot to add the () to var y = new scala.collection.mutable.ListBuffer[ Apple] and it should have rather been
var y = new scala.collection.mutable.ListBuffer[ Apple]()
And like specified in the comments the operator should have been +=

Answer 1

Mutable collections that you can append elements to on the right are of type Growable, and appending is done with addOne. Not every Seq is Growable -- an ArraySeq for example is is a mutable Seq backed by a fixed size array, and while you can change its elements, you can't append to it. You could use for example an ArrayBuffer instead
import scala.collection.mutable.ArrayBuffer
case class Apple(id: Int, color: String)
val sequence: ArrayBuffer[Apple] = ArrayBuffer.empty
for(a<-1 to 4) {
sequence.addOne(Apple(a, "green"))
println("$$$$")
}
print(sequence)
if you want to iteratively build a collection, consider using a Builder instead.

Answer 2

There is a better, functional way to do this:
List.tabulate(4)(a => Apple(a+1,"green"))
tabulate creates a List of a given size and allows you to initialise elements of the list based on their index.