ioc__template_pattern.kt

class Report(
    val women: List<Person>,
    val men: List<Person>
) {
    fun isEmpty(): Boolean {
        return women.isEmpty() && men.isEmpty()
    }
}

abstract class ReportGenerator(
    private val repository: Repository
) {

    fun create(): Report {
        val people = repository.fetchAllPeople()

        val rawReport = splitByGender(people)
        if (rawReport.isEmpty()) {
            return rawReport
        }

        val filteredReport = filter(rawReport)
        return sortByName(filteredReport)
    }

    abstract fun filter(report: Report): Report

    // ...
}

class AdultsReportGenerator(repository: Repository) : ReportGenerator(repository) {

    override fun filter(report: Report): Report {
        val over21 = { person: Person -> person.age > 21 }
        return Report(
            report.women.filter(over21),
            report.men.filter(over21)
        )
    }
}

// example:
val generator = AdultsReportGenerator(repository)
val reportWithPeopleOver21 = generator.create()