Kotlin - Understanding Getters and Setters - kotlin

Question

Kotlin auto-generates it's getters and settings, but I never refer to them? Also, what is the correct way to write a custom getter/setter in Kotlin? When I say myObj.myVar = 99 I feel like myVar is a public field of myObj that I'm accessing directly? What is actually happening here?

Answer 1

This has been answered in a few places, but I thought that I would share a concrete example for people transitioning to Kotlin from Java/C#/C/C++, and who had the same question that I did:
I was having difficulty in understanding how getters and setters worked in Kotlin, especially as they were never explicitly called (as they are in Java). Because of this, I was feeling uncomfortable, as it looked like we were just directly referring to the vars/vals as fields. So I set out a little experiment to demonstrate that this is not the case, and that in fact it is the implicit (auto-generated) or explicit getter/setter that is called in Kotlin when you access a variable/value. The difference is, you don't explicitly ask for the default getter/setter.
From the documentation - the full syntax for declaring a property is:
var <propertyName>: <PropertyType> [= <property_initializer>]
[<getter>]
[<setter>]
And my example is
class modifiersEg {
/** this will not compile unless:
* - we assign a default here
* - init it in the (or all, if multiple) constructor
* - insert the lateinit keyword */
var someNum: Int?
var someStr0: String = "hello"
var someStr1: String = "hello"
get() = field // field is actually this.someStr1, and 'this' is your class/obj instance
set(value) { field = value }
// kotlin actually creates the same setters and getters for someStr0
// as we explicitly created for someStr1
var someStr2: String? = "inital val"
set(value) { field = "ignore you" }
var someStr3: String = "inital val"
get() = "you'll never know what this var actually contains"
init {
someNum = 0
println(someStr2) // should print "inital val"
someStr2 = "blah blah blah"
println(someStr2) // should print "ignore you"
println(someStr3) // should print "you'll never know what this var actually contains"
}
I hope that helps to bring it all together for some others?

Answer 2

Here are some real world examples of custom getters and setters. You can see more here.
// Custom getter example
val friendlyDescription get(): String {
val isNeighborhood = district != null
var description = if (isNeighborhood) "Neighborhood" else "City"
description += " in"
if (isNeighborhood) {
description += " $city,"
}
province?.let {
if (it.isNotEmpty()) {
description += " $it,"
}
}
description += " $country"
return description
}
print(myLocation.friendlyDescription) // "Neighborhood in Denver, Colorado, United States"
// Custom setter example
enum class SearchResultType {
HISTORY, SAVED, BASIC
}
private lateinit var resultTypeString: String
var resultType: SearchResultType
get() {
return enumValueOf(resultTypeString)
}
set(value) {
resultTypeString = value.toString()
}
result.resultType = SearchResultType.HISTORY
print(result.resultTypeString) // "HISTORY"