https://medium.com/@fardavide/kotlin-dsl-builder-pattern-by-delegation-pt-1-9417cd2a514b

mediumBuilderDelegation_1_3.kt

class NotificationBuilder( private val context: Context ) {
   
    var title: String? = null
    @get: StringRes titleRes: Int? = null
    ...
    
    fun build() : Notification {
        val notificationTitle = title 
            ?: titleRes?.let { context.getString( titleRes ) }!!
        ...
        
        return notification
    }
}