What is the right way of using “greater than”, “less than” comparison on nullable integers in Kotlin?

Question

var _age: Int? = 0

public var isAdult: Boolean? = false
   get() = _age?.compareTo(18) >= 0 

This still gives me a null-safety, compile error,

Answer 1

You could possibly use the built-in function compareValue:

fun > compareValues(a: T?, b: T?): Int

public var isAdult: Boolean = false
   get() = compareValues(_age, 18) >= 0

or

public var isAdult: Boolean = false
   get() = compareValues(18, _age) <= 0

Note however that null is considered less than any value, which may suit your case, but may lead to undesired behavior in other cases. E.g., think of var grantMinorsDiscount.