Local late initialization in Kotlin

Question

How can I late-initialize a variable in a funtion, since lateinit is not allowed for local variables? Otherwise, what is the good pattern for this case:

private fun displaySelectedScreen(itemID: Int) {
    //creating fragment object
    val fragment: Fragment
    //initializing the fragment object which is selected
    when (itemID) {
        R.id.nav_schedule -> fragment = ScheduleFragment()
        R.id.nav_coursework -> fragment = CourseworkFragment()
        R.id.nav_settings -> {
            val i = Intent(this, SettingsActivity::class.java)
            startActivity(i)
        }
        else -> throw IllegalArgumentException()
    }
    //replacing the fragment, if not Settings Activity
    if (itemID != R.id.nav_settings) {
        val ft = supportFragmentManager.beginTransaction()
        ft.replace(R.id.content_frame, fragment)// Error: Variable 'fragment' must be initialized
        ft.commit()
    }
    drawerLayout.closeDrawer(GravityCompat.START)
}

Answer 1

when is an expression, so

val fragment: Fragment = when (itemID) {
    R.id.nav_schedule -> ScheduleFragment()
    R.id.nav_coursework -> CourseworkFragment()
    ...
    else -> throw IllegalArgumentException()
}

will work for this use case.

There is no lateinit equivalent for local variables. Other language constructs like try or if are expressions as well, so this is never needed.

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Update 2017-11-19

Kotlin 1.2 supports lateinit for local variables, so

lateinit val fragment: Fragment

works starting with Kotlin 1.2.