Second argument replacing first scala - arrays

Question

I am trying to define a function in scala ( ^ ), which takes 2 values and prints them like
2
x
Here is what I have so far...
class $ (val text2D: Array[Array[Char]])
{
def ^(that: $) =
{
" " ++ s"${this.text2D(0)(0)}" ++
"\n" ++ s"${that.text2D(0)(0)}"
}
def +(that: $) = this.text2D + "+" + that.text2D
override def toString = s"${this.text2D(0)(0)}"
}
object $ {
val array = Array.ofDim[Char](1,1)
def apply(x: String): $ = {
array (0)(0) = x.charAt(0)
new $ (array)
}
}
val x = $("x")
println(x)
val x2 = $("x") ^ $("2")
println(x2)
When I run this, I do not get the output I am expecting, instead I get
2
2
Why is it only taking the second element? Any help would be appreciated.

Answer 1

object creates a singleton, so the (mutable) array that you use is shared between calls to apply. You need to allocate that array inside the apply call.
def apply(x: String): $ = {
val array = Array.ofDim[Char](1,1)
array (0)(0) = x.charAt(0)
new $ (array)
}
Also, slightly unrelated, but I believe you have your arguments backward. To get the output you want, you need
" " ++ s"${that.text2D(0)(0)}" ++
"\n" ++ s"${this.text2D(0)(0)}"

Answer 2

I think what you need is something like this:
class $(val text2D: Array[String]) {
def ^(that: $): $ = {
if (this.text2D.length == 0)
that
else if (that.text2D.length == 0)
this
else {
val thisW = this.text2D(0).length
val thatW = that.text2D(0).length
// cross-pad arrays to have the same width
val padThisRight = " " * thatW
val padThatLeft = " " * thisW
val thisPaddedW = this.text2D.map(_ + padThisRight)
val thatPaddedW = that.text2D.map(padThatLeft + _)
// first lines comes from that!
new $(thatPaddedW ++ thisPaddedW)
}
}
def +(that: $): $ = {
if (this.text2D.length == 0)
that
else if (that.text2D.length == 0)
this
else {
val thisH = this.text2D.length
val thatH = that.text2D.length
val thisW = this.text2D(0).length
val thatW = that.text2D(0).length
// pad arrays to have the same height
val emptyThis = " " * thisW
val emptyThat = " " * thatW
val thisPaddedH = if (thisH >= thatH) this.text2D else Array.fill(thatH - thisH)(emptyThis) ++ this.text2D
val thatPaddedH = if (thisH <= thatH) that.text2D else Array.fill(thisH - thatH)(emptyThat) ++ that.text2D
new $(thisPaddedH.zip(thatPaddedH).map(p => p._1 + p._2))
}
}
override def toString = text2D.mkString("\n")
}
object $ {
def apply(x: String): $ = {
new $(Array[String](x))
}
}
and then
val x2 = $("x") ^ $("2")
println(s"x2:\n$x2")
println("----------------------------")
val z = x2 + $(" + ") + y2
println(s"z:\n$z")
println("----------------------------")
val zz = x2 + $(" + ") + (y2 ^ $("3"))
println(s"zz:\n$zz")
println("----------------------------")
produces following output
x2:
2
x
----------------------------
z:
2 2
x + y
----------------------------
zz:
3
2 2
x + y
----------------------------
The main idea here is that operations on $ produce another instance of $ rather than String (I use String instead of Array[Char] as it seems much easier and has no obvious drawbacks). In such way you don't have to re-parse String splitting it by new lines and have to wonder how to handle cases when the string is not well-aligned. So now operators ^ and + is just an exercise in aligning two 2d-arrays to have either the same width or the same height and then joining them.