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

A generic and flexible solution would be:

infix fun > T?.isGreaterThan(other: T?): Boolean? =
    if (this != null && other != null) this > other else null

infix fun > T?.isGreaterThanOrEqual(other: T?): Boolean? =
    if (this != null && other != null) this >= other else null

infix fun > T?.isLessThan(other: T?): Boolean? =
    if (this != null && other != null) this < other else null

infix fun > T?.isLessThanOrEqual(other: T?): Boolean? =
    if (this != null && other != null) this <= other else null

Depending on your needs, you could use it as:

public var isAdult: Boolean? = false
    get() = _age isGreaterThanOrEqual 18

or:

public var isAdult: Boolean = false
    get() = _age isGreaterThanOrEqual 18 == true