Nice! You could also potentially return FragmentTransaction from your lambda extension and then have your transaction chain like it does currently

inline internal fun FragmentManager.transaction(func: FragmentTransaction.() -> FragmentTransaction) {
   // Chained
   beginTransaction().func().commit()
}

Anyone reading may be interested to see you can do a similar thing with SharedPreferences:

inline internal fun SharedPreferences.applyMe(func: SharedPreferences.Editor.() -> SharedPreferences.Editor) {
    this.edit().func().apply()
}
preferences.applyMe { 
    putBoolean("SOMETHING", true)
}