Kotlin Extension Functions Databinding

You have to import CityKt firstly into xml

<import type="my.package.domain.country.model.CityKt" />

int the data section
then you can use it like this

<TextView
  android:id="@+id/city"
  android:layout_width="wrap_content"
  android:layout_height="wrap_content"
  android:text="@{CityKt.streetName(city)}" />

If you review CityKt you will see that there is static Java method with City as first argument