Kotlin extension function to use in compareTo when sorting requires multiple items.

kotlin-compare.kt

inline fun <T> T.ifZero(exp: Int, block: T.() -> Int): Int = if (exp == 0) block() else exp


// using
data class User(
	val firstName: String,
	val lastName: String,
	val dateOfBirth: Date
) : Comparable<User> {
	// classic comparator.
    override fun compareToB(other: User): Int {
        var result = firstName.compareTo(other.firstName, true)
        if(result == 0) {
            result = lastName.compareTo(other.lastName, true)
            if(result == 0) {
                result = dateOfBirth.compareTo(other.dateOfBirth)
            }
        }
        return result
    }
	// lambda comparator
    override fun compareToA(other: User): Int =
        ifZero(firstName.compareTo(other.firstName, true)) {
            ifZero(lastName.compareTo(other.lastName, true)) {
                dateOfBirth.compareTo(other.dateOfBirth)
            }
        }    
}