Stringbuilder - Replacing all instances of one character with another** - scala

Question

First time posting on here, let me know if I need to change my format and I will do so.
I need to extract a defined region from the buffer, and apply code that will substitute character 'x' with character 'y', which I have attempted below:
buffer.substring(lwr,upr).replace(s,t)
However that fails all of my JUNIT tests and I can't wrap my head around why.
Does anybody have any pointers? Thank you!
EDIT:
For example, given the following:
a p p r o p r i a t e (Marker position is 2, cursor position is 6)
^ ^
Doing "subChar('p', 'x') should result in this being the output:
a p x r o x r i a t e (Marker position and cursor position DO NOT CHANGE)
^ ^

Answer 1

If you take a string, then substring something, then invoke replace on the result, the resulting string will have nothing to do with the original string, thus your solution obviously cannot work.
The indexing scheme from the linked answer remains the same, the answer is easily generalizable to arbitrary functions that can be applied to characters:
def mapBetween(str: String, start: Int, end: Int)(f: Char => Char) = {
val (a, bc) = str.splitAt(start)
val (b, c) = bc.splitAt(end - start)
a + b.map(f) + c
}
def replaceBetween(str: String, start: Int, end: Int, what: Char, byWhat: Char): String = {
mapBetween(str, start, end){ c =>
if (c == what) byWhat else c
}
}
With the above definitions, this here:
println(replaceBetween("appropriate", 2, 6, 'p', 'x'))
produces:
apxroxriate

Answer 2

I think your problem is your Buffer, I created a ScalaFiddle that demonstrates it for simple String and a simple List implementation:
val str = "appropriate"
println (str.replace('p', 'x')) // axxroxriate
val list = str.toList.map{
case c if c == 'p' => 'x'
case c => c
}
println (list) // List(a, x, x, r, o, x, r, i, a, t, e)
Check your implementation or add your implementation to your question.
Here is the example with a region:
def replaceBetween(str: String, start: Int, end: Int, what: Char, byWhat: Char): String = {
val prefix = str.take(start)
val postfix = str.drop(end)
val toMap = str.drop(start).take(end-start).replace(what, byWhat)
prefix + toMap + postfix
}
println(replaceBetween("appropriate", 2, 6, 'p', 'x'))
Here you can try yourself: ScalaFiddle