Kotlin and swift full map navigation speed

Question

I'm trying to understand what is the best way to navigate maps in kotlin (and swift), when you need to navigate the whole map. Both languages offer a .values method that make the navigation simpler, but with a C++ background I thought it could not perform in a decent way since it should create a vector of values with an additional navigation of the map (and a relevant memory allocation).

Basically my question is about this code:

val map: MutableMap<Int, String> = mutableMapOf()

for (i in 1.. 1000000) {
    map[i] = "Value of this element is $i"
}

for (v in map.values)
    if (v[0] != 'V')
        Log.e(TAG, "ERROR!")

for ((_, v) in map) // it should be faster!
    if (v[0] != 'V')
        Log.e(TAG, "ERROR!")

... I've done a few benchmark of this code, timing the results with System.currentTimeMillis() and using one or two different maps, to avoid cache effects...

But I cannot get meaningful results... here is a complete program in kotlin native, that shows (differently from kotlin on JVM) a behaviour that is the contrary of the one I expected, I used two different maps and two tests per algorithm to exclude cache advantages.

import kotlin.system.*

fun main() {
    val m1 : MutableMap<Int, String> = mutableMapOf()
    val m2 : MutableMap<Int, String> = mutableMapOf()

    println("Creating map...")
    var st = getTimeMillis()
    for (i in 1..2000000) {
        m1[i] = "Test $i"
        m2[i] = "Test $i"
    }

    var end = getTimeMillis()
    println("Took: ${end - st} msecs, map size: ${m1.size},${m2.size} elements")

    st = getTimeMillis()
    for ((_, v) in m1)
        if (v[0] != 'T')
            println("ERROR!");
    end = getTimeMillis()
    println("Algorithm 1 (k,v): ${end - st} msecs")

    st = getTimeMillis()
    for (v in m2.values)
        if (v[0] != 'T')
            println("ERROR!");
    end = getTimeMillis()
    println("Algorithm 2 (values): ${end - st} msecs")

    st = getTimeMillis()
    for ((_, v) in m2)
        if (v[0] != 'T')
            println("ERROR!");
    end = getTimeMillis()
    println("Algorithm 1bis (k,v): ${end - st} msecs")

    st = getTimeMillis()
    for (v in m1.values)
        if (v[0] != 'T')
            println("ERROR!");
    end = getTimeMillis()
    println("Algorithm 2bis (values): ${end - st} msecs")
}