In different Kotlin examples for Android I see toast("Some message...") or toastLong("Some long message"). For example:
It can be an extension function for Context:
fun Context.toast(message: CharSequence) =
Toast.makeText(this, message, Toast.LENGTH_SHORT).show()
You can place this anywhere in your project, where exactly is up to you. For example, you can define a file mypackage.util.ContextExtensions.kt and put it there as a top level function.
Whenever you have access to a Context instance, you can import this function and use it:
import mypackage.util.ContextExtensions.toast
fun myFun(context: Context) {
context.toast("Hello world!")
}