In Kotlin How Can I Convert an Int? to an Int

Question

I'm using a HashMap<Int, Int> in Kotlin and when I get out of it the return type is Int?.

How can I convert the Int? to an Int?

So far I've tried using Int?.toInt(), but that seems to be returning an Int?.

I'm writing a Fibonacci function, and my code looks like:

val fibMemo : Map<Int, Int> = HashMap<Int,Int>() fun fibN(n:Int) : Int {     if (n == 0 || n == 1) return 1     if (fibMemo.containsKey(n))         // Error here: Type mismatch: inferred type is Int? but Int was expected         return fibMemo.get(n)?.toInt()     else {         val newNum : Int = fibN(n-1) + fibN(n-2)         fibMemo.put(n, newNum)         return newNum     } } 

Answer 1

The direct answer, use the !! operator to assert that you trust a value is NOT null and therefore changing its type to the non null equivalent. A simple sample showing the assertion allowing the conversion (which applies to any nullable type, not just Int?)

val nullableInt: Int? = 1 val nonNullableInt: Int = nullableInt!! // asserting and smart cast 

Another way to convert a value is via a null check. Not useful in your code above, but in other code (see Checking for null in conditions):

val nullableInt: Int? = 1 if (nullableInt != null) {    // allowed if nullableInt could not have changed since the null check    val nonNullableInt: Int = nullableInt } 

This questions is also answered by the idiomatic treatment of nullability question: In Kotlin, what is the idiomatic way to deal with nullable values, referencing or converting them