Why I'm getting 'return' expression required in a function with a block body error in Kotlin? - kotlin

Question

open class Test1 {
fun name(a: Int, b: Int): Int {
if (a % 2 == 0 && b % 2 == 0) return (a * b)
if (a % 2 == 1 && b % 2 == 1) return (a + b)
if ((a % 2 == 0).xor(b % 2 == 0)) return if (a > b) (a - b) else (b - a)
}
}
class Test2 : Test1() {
}
val obj1 = Test2()
print(obj1.name(7 , 8))
I'm trying to learn inheritance in Kotlin, but when I call name function from father class and try to print the result I get error below.
error: a return expression required in a function with a block body ('{...}') }

Answer 1

If the first and the second condition is false, the third one must be true so you can remove the last condition. The compiler does not seem to be able to draw this conclusion, so it suspects a case where there is no return.
fun name(a: Int, b: Int): Int {
if (a % 2 == 0 && b % 2 == 0) return (a * b)
if (a % 2 == 1 && b % 2 == 1) return (a + b)
return if (a > b) (a - b) else (b - a)
}
You can also simplify this method as follows
fun name(a: Int, b: Int): Int {
if (a % 2 != b % 2) return if (a > b) (a - b) else (b - a);
return if (a % 2 == 0) (a * b) else (a + b)
}

Answer 2

Your last line of the function
if ((a % 2 == 0).xor(b % 2 == 0)) return if (a > b) (a - b) else (b - a)
if you add brackets for clarity, it would look like:
if ((a % 2 == 0).xor(b % 2 == 0)) {
return if (a > b) (a - b) else (b - a)
}
So if the if test is false, the code won't run, which means you've reached the end of the function and still haven't returned something. You have to return an Int.

Answer 3

As already answered, in order for your code to compile your function must return an int from all execution paths, your function doesn't satisfy that condition. what happens if all the if conditions eveluate to false?
And second thing is that in kotlin return is an expression, so you can lift it out like so
fun name(a: Int, b: Int): Int {
return if (a % 2 == 0 && b % 2 == 0) { (a * b) }
else if (a % 2 == 1 && b % 2 == 1) { (a + b) }
else if ((a % 2 == 0).xor(b % 2 == 0)) { if (a > b) (a - b) else (b - a) }
else SOME_DEFAULT_INT
}