How do I get rid of Boolean method is always inverted warning? - kotlin

Question

fun findError(puzzle: Array<IntArray>): Boolean {
for (z in 0..8) {
val blockNums = mutableListOf<Int>()
val xNums = mutableListOf<Int>()
val yNums = mutableListOf<Int>()
for (index in 0..8) {
xNums.add(puzzle[z][index])
yNums.add(puzzle[index][z])
blockNums.add(puzzle[blocks.xy[z + 1][index]][blocks.xy[z][index]])
if (blockNums.count() != blockNums.toSet().count() ||
yNums.count() != yNums.toSet().count() ||
xNums.count() != xNums.toSet().count()) return false
}
}
return true
}
This function works as desired but the Intellij IDE gives this warning. "Boolean method 'findError' is always inverted". I kind of understand what it means and I know I could suppress it.
I can't figure out how to rewrite the code block to satisfy the error and not change the functionality. Should I just suppress it or is there a more proper way to express this? I'm a beginner that is learning.
public final data class Blocks public constructor(blockNums: kotlin.collections.MutableList<kotlin.Int>, blockNumsFinal: kotlin.collections.MutableSet<kotlin.Int>, xy: kotlin.collections.List<kotlin.collections.List<kotlin.Int>>) {
public final val blockNums: kotlin.collections.MutableList<kotlin.Int> /* compiled code */
public final val blockNumsFinal: kotlin.collections.MutableSet<kotlin.Int> /* compiled code */
public final var xy: kotlin.collections.List<kotlin.collections.List<kotlin.Int>> /* compiled code */
public final operator fun component1(): kotlin.collections.MutableList<kotlin.Int> { /* compiled code */ }
public final operator fun component2(): kotlin.collections.MutableSet<kotlin.Int> { /* compiled code */ }
public final operator fun component3(): kotlin.collections.List<kotlin.collections.List<kotlin.Int>> { /* compiled code */ }
}
I found a way to rewrite the function not using the '!' symbol. This should satisfy the intention of the warning to use positives instead of negatives. It still gives the warning. I think Bas Leijdekkers comment about the inspection may be correct.
fun findError(puzzle: Array<IntArray>): Boolean {
val blockNums = mutableListOf<Int>()
val xNums = mutableListOf<Int>()
val yNums = mutableListOf<Int>()
var counts = 0
for (z in 0..8) {
blockNums.clear()
xNums.clear()
yNums.clear()
for (index in 0..8) {
xNums.add(puzzle[z][index])
yNums.add(puzzle[index][z])
blockNums.add(puzzle[blocks.xy[z + 1][index]][blocks.xy[z][index]])
if (blockNums.count() == blockNums.toSet().count() &&
yNums.count() == yNums.toSet().count() &&
xNums.count() == xNums.toSet().count()) {
counts++
}
}
}
return counts == 81
}

Answer 1

Which line is the IntelliJ warning you about, is it this statement?
if (blockNums.count() != blockNums.toSet().count() ||
yNums.count() != yNums.toSet().count() ||
xNums.count() != xNums.toSet().count()) return false
if so, it is because this is complex and likely difficult for someone other than you to understand. Here's two ideas about how you might make reduce the complexity:
(1)
if (blockNums.size != blockNums.toSet().size) return false
if (yNums.size != yNums.toSet().size) return false
if (xNums.size != xNums.toSet().size) return false
or (2)
val blocksDiffer = (blockNums.size != blockNums.toSet().size)
val yDiffer = (yNums.size != yNums.toSet().size)
val xDiffer = (xNums.size != xNums.toSet().size)
if(blocksDiffer || yDiffer || xDiffer) return false
(There is a small performance penalty with (2) since the program has to compute all 3 evaluations.
I also changed count() to size which are equivalent)

Answer 2

I believe this is IntelliJ trying to warn you that a boolean method result is always inverted after calling. In other words, you only ever use !findError() in your code.
This is an indication that the code could be made more readable by using positive language. JetBrain's justification for this appears to be based on Robert Martin's book Clean Code:
“Negatives are just a bit harder to understand than positives. So, when possible, conditionals should be expressed as positives.”
You can use Refactor -> Invert Boolean... to perform this automatically.