...

sealed class Section
object Home : Section()
object Settings : Section()

...

private fun changeSection(section: Section) {
    if (currentSection == section) {
        return // nothing to do
    }
    currentSection = section
    when (section) {
        is Home -> supportFragmentManager.switchFragmentTo("HOME") { HomeFragment() }
        is Settings -> supportFragmentManager.switchFragmentTo("SETTINGS") { SettingsFragment() }
    }
}

...