Test

package com.example

class Test {
   operator fun String.get(range: IntRange) = substring(range)
}

class Test2 {
   companion object {
       operator fun String.get(range: IntRange) = substring(range)
   }
}

fun main() {
   val x = "test"
   val y = with(Test()) { x[2..3] }
   val z = with(Test2) { x[2..3]}
}

get

with

Test().get()

Test()."test"[]

get