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In Kotlin, how do you refer to a variable from outside a scoping function when it has the same name as a field in the lambda receiver

In Kotlin, using a scope function such as "with" that allows the this reference inside the block to reference the lambda result, is it possible to reference the outer class member when it has the same name as one of the fields in the result?
eg
data class Person(name: String)
...
class MyClass {
var name = ""
with(personRepository.getPerson(personId)) {
// How do we set the class "name" member - "this.name" or just "name" refers to the scoped object?
name = this.name // ???
}
Obviously using a different variable name is the simple workaround but just wondering if there is a syntax for when the variables have the same name
class MyClass {
var personName = ""
...
with(personRepository.getPerson(personId)) {
personName = this.name
}

the this refers to the object that you pass. In order for you to refer to the context of your class you would need to use labels like below. Do note that this is an anti pattern. With scoping functions you would only want to apply logic on the object that you are passing or that is the receiver object in scoping functions like let and apply
class MyClass {
var name: String = ""
val person = Person("my name")
fun setName() = with(person) {
this#MyClass.name = person.name
}
}

I would suggest using let{} instead of with{}:
data class Person(name: String)
...
class MyClass {
var name = ""
personRepository.getPerson(personId).let {
name = it.name
}

You can use a labeled this to refer to the variable in MyClass. Like this:
with(personRepository.getPerson(personId)) {
this#MyClass.name = name
}

Reference an object in a class by using a string?

I want to reference an object within this class I have below:
class HerbData {
object Dill {
const val herbName: String = "This is Dill!"
const val scientificName: String = "Anethum Graveolens"
val dullThumbnail: Int = R.drawable.dill_thumbnail_attr
}
object Peppermint {
val herbName: String = "This is Peppermint!"
}
}
Is there anyway that I can reference the object by using a string in Kotlin? Here is somewhat what I mean:
HerbData."Dill".herbname
I can't find anything on this topic for Kotlin.

Another way you could do this is with an enum class. The advantage over a map is that you have a data structure you can reference directly in code, so you could use HerbData.Dill as well as HerbData["Dill"]. And that will enable you to take advantage of compile-time checking and lint warnings, refactoring, exhaustive pattern matching, code completion etc, because the data is defined in your code
enum class HerbData(
val herbName: String,
val scientificName: String? = null,
val dullThumbnail: Int? = null
) {
Dill("This is Dill!", "Anethum Graveolens", R.drawable.dill_thumbnail_attr),
Peppermint("This is Peppermint!");
companion object {
operator fun get(name: String): HerbData? =
try { valueOf(name) } catch(e: IllegalArgumentException) { null }
}
}
fun main() {
// no guarantee these lookups exist, need to null-check them
HerbData["Peppermint"]?.herbName.run(::println)
// case-sensitive so this fails
HerbData["peppermint"]?.herbName.run(::println)
// this name is defined in the type system though! No checking required
HerbData.Peppermint.herbName.run(::println)
}
>> This is Peppermint!
null
This is Peppermint!
Enum classes have that valueOf(String) method that lets you look up a constant by name, but it throws an exception if nothing matches. I added it as a get operator function on the class, so you can use the typical getter access like a map (e.g. HerbData["Dill"]). As an alternative, you could do something a bit neater:
companion object {
// storing all the enum constants for lookups
private val values = values()
operator fun get(name: String): HerbData? =
values.find() { it.name.equals(name, ignoreCase = true) }
}
You could tweak the efficiency on this (I'm just storing the result of values() since that call creates a new array each time) but it's pretty simple - you're just storing all the enum entries and creating a lookup based on the name. That lets you be a little smarter if you need to, like making the lookup case-insensitive (which may or may not be a good thing, depending on why you're doing this)
The advantage here is that you're generating the lookup automatically - if you ever refactor the name of an enum constant, the string label will always match it (which you can get from the enum constant itself using its name property). Any "Dill" strings in your code will stay as "Dill" of course - that's the limitation of using hardcoded string lookups
The question really is, why do you want to do this? If it's pure data where no items need to be explicitly referenced in code, and it's all looked up at runtime, you should probably use a data class and a map, or something along those lines. If you do need to reference them as objects within the code at compile time (and trying to use HerbData."Dill".herbName implies you do) then an enum is a fairly easy way to let you do both

Declare a Data Class
data class HerbData (
val scientificName: String,
val dullThumbnail: Int
)
Initialize a muteable map and put data in it
val herbData = mutableMapOf<String, HerbData>()
herbData.put("Dill", HerbData("Anethum Graveolens", R.drawable.dill_thumbnail_attr))
herbData.put("Peppermint", HerbData("Mentha piperita", R.drawable.peppermint_thumbnail_attr))
You can now just
herbData["Dill"]?.scientificName

class HerbData {
interface Herb {
val herbName: String
val scientificName: String
}
object Dill : Herb {
override val herbName: String = "This is Dill!"
override val scientificName: String = "Anethum Graveolens"
}
object Peppermint: Herb {
override val herbName: String = "This is Peppermint!"
override val scientificName: String = "Mentha piperita"
}
companion object {
operator fun get(name: String): Herb? {
return HerbData::class
.nestedClasses
.find { it.simpleName == name }
?.objectInstance as? Herb
}
}
}
println(HerbData["Dill"]?.herbName) // Prints: This is Dill!
println(HerbData["Peppermint"]?.scientificName) // Prints: Mentha piperita
println(HerbData["Pepper"]?.herbName) // Prints: null

kotlin bound class reference and generics

I'm switching to Kotlin for Android, but I'm struggling to understand the behavior of generics and Bound Class References.
In java I can serialize an object using Moshi's lib with the following lines:
Moshi moshi = new Moshi.Builder().build();
String string = moshi.adapter(CredentialsResponse.class).toJson(body);
And in Kotlin:
val moshi = Moshi.Builder().build()
var string = moshi.adapter(CredentialsResponse::class.java).toJson(body)
If I want to get the class from an instance, I found two options, but one is not working, and I can't understand why:
This code works:
fun testStack(body: CredentialsResponse) {
val moshi = Moshi.Builder().build()
var string = moshi.adapter(body.javaClass).toJson(body)
}
but this code shows a type mismatch error
fun testStack(body: CredentialsResponse) {
val moshi = Moshi.Builder().build()
var string = moshi.adapter(body::class.java).toJson(body)
}
AFAIK, this call is allowed since 1.1 (https://kotlinlang.org/docs/reference/reflection.html#bound-class-references-since-11), so what am I missing?

There's a subtle difference between the two:
class K
val javaClass: JsonAdapter<K> = moshi.adapter(body.javaClass)
val classJava: JsonAdapter<out K> = moshi.adapter(body::class.java)
Note that body::class.java is marked with out
By calling moshi.adapter(body::class.java).toJson(body) you're try to pass body as in parameter

The difference is, as #AlexeySoshin noted, that the unbound class reference Foo::class is typed with the exact type of the referenced class KClass<Foo>, and the bound one is typed with an out-projection: KClass<out Foo>.
There is a strong reason for this difference. When you reference a class by its name, you can be sure that the class token the reference evaluates to designates exactly the referenced type.
But, when you get a bound class reference for an expression typed as Foo, the expression may evaluate to an instance of Foo's subtype, and the correct type for the type token is KClass<out Foo>, meaning exactly that the actual type argument may be Foo or its subtype.
See this answer for another detailed explanation of the difference between bound and unbound class references: (link)

Data class inheriting from Java class

I have a data class in Kotlin that inherits from a Java class, which defines a constructor with 1 argument,
public BaseClass(String userSessionId) {
this.userSessionId = userSessionId;
}
My Kotlin class is defined as this
class DerivedClass(
userSessionId: String,
var other: Other? = null
) : BaseClass(userSessionId) {
I can't define it as a data class because of userSessionId, which Kotlin requires to be a val or var in data classes. However, if I do so, then Retrofit throws an exception because there are 2 members named userSessionId. Is there a way to have a data class inherit from a Java class with a constructor taking arguments? Note that I cannot change the base class.
A possible solution is to define a dummy val to avoid the name clash, but this is less than ideal
data class DerivedClass(
val dummy: String,
var other: Other? = null
) : BaseClass(dummy) {

You can use the transient keyword in Java to ignore a field during serialization, this can be done in Kotlin by using the #Transient annotation on the property instead.

In which situation val/var is necessary in Kotlin constructor parameter?

Right code:
class MainActHandler(val weakActivity: WeakReference<Activity>): Handler() {
override fun handleMessage(msg: Message?) {
val trueAct = weakActivity.get() ?: return
if (msg?.what == ConversationMgr.MSG_WHAT_NEW_SENTENCE){
val sentence = msg.obj as String?
trueAct.conversation.text = sentence
}
super.handleMessage(msg)
}
}
cannot be resolved code:
class MainActHandler(weakActivity: WeakReference<Activity>): Handler() {
override fun handleMessage(msg: Message?) {
val trueAct = weakActivity.get() ?: return
if (msg?.what == ConversationMgr.MSG_WHAT_NEW_SENTENCE){
val sentence = msg.obj as String?
trueAct.conversation.text = sentence
}
super.handleMessage(msg)
}
}
cannot be resolved code screenshot
The only difference is the "val" has been deleted and cannot be resolve.
Which might be important is that it's a inner class.
BUT
This one class without "val/var" in constructor parameter is working:
class BookInfo(convrMgr: ConversationMgr, id: String, queue: RequestQueue, queueTag:String) {
val TAG = "BookInfo"
var title: String? = ""
init {
val url = "https://api.douban.com/v2/book/$id"
// Request a string response from the provided URL.
val stringRequest = StringRequest(Request.Method.GET, url,
Response.Listener<String> { response ->
Log.d(TAG + " Response", response.substring(0))
// Parse JSON from String value
val parser = Parser()
val jsonObj: JsonObject =
parser.parse(StringBuilder(response.substring(0))) as JsonObject
// Initial book title of book properties.
title = jsonObj.string("title")
Log.d(TAG + " Book title", title)
convrMgr.addNewMsg(title)
},
Response.ErrorListener { error -> Log.e(TAG + " Error", error.toString()) })
// Set the tag on the request.
stringRequest.tag = queueTag
// Add the request to the RequestQueue.
queue.add(stringRequest)
}
}
And if I add var/val before "queue: RequestQueue", I'll get suggestion:
"Constructor parameter is never used as a property less. This inspection reports primary constructor parameters that can have 'val' or 'var' removed. Unnecessary usage of 'val' and 'var' in primary constructor consumes unnecessary memory."
I am just confused about it.

When you write val/var within the constructor, it declares a property inside the class. When you do not write it, it is simply a parameter passed to the primary constructor, where you can access the parameters within the init block or use it to initialize other properties. For example,
class User(val id: Long, email: String) {
val hasEmail = email.isNotBlank() //email can be accessed here
init {
//email can be accessed here
}
fun getEmail(){
//email can't be accessed here
}
}
Constructor parameter is never used as a property
This suggestion is saying that you do not use this property in place apart from the initialization. So, it suggests you to remove this property from the class.

Constructor parameters must use var or val when they are used as a property elsewhere in the class. They do not need to be properties if they are only used for class initialization.
In the example below, the parameter must be a property (var or val) because it is used in a method:
class A(val number: Int) {
fun foo() = number
}
In this other example, the parameter is only used to initialize the class, so it does not need to be a property:
class B(number: Int): A(number) {
init {
System.out.println("number: $number")
}
}

This might be a late answer but the magic lies under the hood:
Based on #BakaWaii's answer:
Putting var/val will make the variable a property of the class and not putting it will make it a parameter of only the constructor function.
So what does it mean, to understand lets look into some code:
class Test(a: Int){}
Now Lets see the decompiled java code:
public final class Test {
public Test(int a) {
}
}
So now if I try to access a using the object of Test() like the below code:
Test t = new Test(10);
t.a //Error
It will give me error. Unresolved reference: a. Why because a is a parameter of the constructor only.
Now if we put var/val in the paramater like below:
class Test(var a: Int){}
The decompliked Java code will become:
public final class Test {
private int a;
public final int getA() {
return this.a;
}
public final void setA(int var1) {
this.a = var1;
}
public Test(int a) {
this.a = a;
}
}
Thus it will not only give you a class property but also give you getter/setters for setting the values.
Now the next question arises if the field a is private how can it be accessed. Simple answer in Java you cannot, i.e. if you are calling the KT class from a Java you will not be able to assign value of a like Test(1).a = 10 but will have to use Test(1).setA(5).
But as kotlin internally handles getters/setters Test(1).a = 5 will be ok.

For #Parcelize to work you need to open up the super's properties and override them in the child:
abstract class Goal(open var number: Int, open var name: String) : Parcelable
#Parcelize
class OperationalGoal(override var number: Int, override var name: String, var description: String) : Goal(number, name)```

In very simple terms, use var or val in class constructor parameters when you want to use that variable, say, inside a method within that class. Thus you're effectively turning them into properties and not just mere constructor or method parameters.
class User(var name: String, age: Int) {
var str = "John"
var num = 18
fun setName(){
name = str // due to using var on our class constructor parameter, we can access the constructor variable *name* inside this setter method. *name* is a property parameter thanks to the var keyword.
}
fun setAge(){
age = num // this will result in a compiler error, because *age* is just a parameter, notice that var wasn't used in the *age* parameter within the class constructor, which means we can't access it like we did with *name*
}
}
Run this Kotlin Playground code to get a clearer idea of what's going on.