`val fullTariffList = arrayOf customer reseller vendor flatMap type gt testTariffList map it copy type = type `

`val fullTariffList = arrayOf customer reseller vendor flatM kotlinlang #announcements

01/19/2018, 5:24 PM

val fullTariffList = arrayOf("customer", "reseller", "vendor").flatMap { type ->  testTariffList.map { it.copy(type = type) } }

01/19/2018, 5:27 PM

Thanks, your solution is perfect) But I also want to understand what is going on in my example)

fullTariffList.add(tariffInfo)

is always contains

vendor

. I think I am missing some knowledge about

forEach

01/19/2018, 5:30 PM

You are basically adding one item three times into the list.

01/19/2018, 5:31 PM

println(tariffInfo);

shows me that tariffInfo is different in every iteration

fullTariffList.add(tariffInfo)

processed after finishing forEach?

May be someone could point me to docs)

01/19/2018, 5:34 PM

class Object { var type: String }

val list = mutableListOf<Object>()
val obj = Object()

obj.type = "1"
println(obj.type) // "1"
list += obj // list has one reference to obj, it's type is "1"

obj.type = "2"
println(obj.type) // "2"
list += obj // list has two reference to the same obj, it's type is "2"

obj.type = "3"
println(obj.type) // "3"
list += obj // list has three reference to the same obj, it's type is "3"

list.forEach {
    println(it.type)
}
// prints "3 3 3", as it's the same object and last value of type was "3"

Does it make this clearer? If you are coming from the language with pointers: your container holds objects by reference, not by value. So

.copy

allows you to create new object every iteration and list would have different objects inside it.

01/19/2018, 5:37 PM

Yeah, I got your example

01/19/2018, 7:33 PM

flatMap

solution creates a list with the same items but in a different order than the original code. Turning it inside out would fix this:

testTariffList.flatMap { item -> arrayOf("customer", "reseller", "vendor").map { item.copy(type = it) } }

01/19/2018, 9:02 PM

in general, order does not matter. Neverthless it's useful example, thanks