how should i access the lateinit property - kotlin

Question

please help me understand how to properly initialize "pets"
class Person:
class Person(
val height: Int,
val weight: Int,
val name: String,
) {
lateinit var pets: HashSet<Animal>
fun buyPet():Unit{
this.pets.add(Animal((0..100).random(), (0..100).random(), getRandomString((3..12).random())))
}
private fun getRandomString(length: Int) : String {
val allowedChars = ('A'..'Z') + ('a'..'z')
return (1..length)
.map { allowedChars.random() }
.joinToString("")
}
}
class Animal:
data class Animal(
val energy:Int,
val weight:Int,
val name:String) {
}
main:
fun main() {
val person1=Person(187, 85, "Denis")
person1.buyPet()
println(person1.pets)
}
I am getting this error
Exception in thread "main" kotlin.UninitializedPropertyAccessException: lateinit property pets has not been initialized
at classes_06.Person.buyPet(Person.kt:35)

Answer 1

Replace
lateinit var pets: HashSet<Animal>
With
val pets = mutableSetOf<Animal>()
In the original code pets is declared, but never initialised, and lateinit is just telling the compiler "do not complain about this, I'll initialise it later". When doing Kotlin, try to avoid using lateinit as much as possible.
This other SO question might give you a bit more info in general terms about what is declaring and initialising a variable.

Answer 2

To complement Agusto’s answer:
Lateinit works in cases on which you can’t define the value of the variable immediately on the object construction, for any reason. Therefore, it expects you to define the value of the lateinit variable at some “late-r” point before you try to do anything else with it.
In your case it seems perfectly fine to define the variable “pets” in construction. So you can remove the lateinit modifier and define it right away as Agusto pointed out.
Or if need lateinit for any reason, you could check if it has been initialized before, and if not, define it in the buyPet() function before performing an “add” to it:
fun buyPet(): Unit{
if(!::pets.isInitialized) {
pets = mutableSetOf<Animal>()
}
this.pets.add(Animal((0..100).random(), (0..100).random(), getRandomString((3..12).random())))
}
See this question for further details about the isInitialized property