How to convert mile to kilometer using kotlin - kotlin

Question

I am new to kotlin... I have no idea how to convert miles to kilometer
MainActivity.kt
import androidx.appcompat.app.AppCompatActivity
import android.os.Bundle
import android.view.View
import android.widget.Button
import android.widget.EditText
import android.widget.TextView
class MainActivity : AppCompatActivity() {
override fun onCreate(savedInstanceState: Bundle?) {
super.onCreate(savedInstanceState)
setContentView(R.layout.activity_main)
val name = findViewById<EditText>(R.id.text1)
val ConvertButton = findViewById<Button>(R.id.btn1)
val displayanswer = findViewById<TextView>(R.id.textView1)
}
}

Answer 1

I don't think that's really a kotlin topic.
It's simply a math problema but here is one way to implement it in kotlin :
Using kotlin extensions you can write a function to convert km to miles and miles to km :
fun Float.toKm() = this * 1.60934
fun Float.toMiles() = this / 1.60934
Now when you will have a float that represent a km you'll be able to invoke .toMiles() and when you'll have a float that represent a miles you'll be able to invoke .toKm().
Here is an example :
val kilometers = 10.0F
val miles = 6.0F
println("km ${kilometers} to miles = ${kilometers.toMiles()}")
println("miles ${miles} to km = ${miles.toKm()}")
If you want to read more about extensions : https://kotlinlang.org/docs/extensions.html#extension-functions

Answer 2

I would suggest you define value classes for your types. You can then add conversion functions and arithmetic operations as well. In this example I have defined the plus operator, but you could build on this to make this more full featured
#JvmInline
value class Kilometer(val value: Float) {
fun toMeters() = Meter(value * 1000f)
operator fun plus(other: Kilometer) = Kilometer(value + other.value)
}
#JvmInline
value class Meter(val value: Float) {
fun toKilometers() = Kilometer(value / 1000f)
fun toMiles() = Mile(value / 1.604f)
}
#JvmInline
value class Mile(val value: Float) {
fun toMeters() = Meter(value * 1.604f)
}
fun useIt() {
val km1 = Kilometer(12f)
val km2 = Kilometer(20f)
val km = km1 + km2
val meters = km.toMeters()
val miles = meters.toMiles()
}