How can you implement creating a new object that has three fields from the source data class and additionally two object fields?

In Kotlin, to create a new object that contains three fields from the original data class and additionally two object fields, you can use copying with the copy() function and class extension or create a new class with the required fields.

Example:

data class Original(val a: Int, val b: String, val c: Double)

data class Additional(val x: String, val y: Int)

// New class combining fields
class Extended(
    val a: Int,
    val b: String,
    val c: Double,
    val additional1: Additional,
    val additional2: Additional
)

// Creating from the original object
val original = Original(1, "text", 2.0)
val add1 = Additional("obj1", 10)
val add2 = Additional("obj2", 20)

val extended = Extended(original.a, original.b, original.c, add1, add2)

If you specifically need a data class with copying, you can do it like this:

data class Extended(
    val a: Int,
    val b: String,
    val c: Double,
    val additional1: Additional,
    val additional2: Additional
)

val extended = Extended(original.a, original.b, original.c, add1, add2)

Thus, you combine the fields of the original class with new objects.