Kotlin Koans - Conventions

#	Kotlin Koans
	Kotlin Koans - Introduction
	Kotlin Koans - Conventions
	Kotlin Koans - Collections
	Kotlin Koans - Properties
	Kotlin Koans - Builders
	Kotlin Koans - Generics

1 Comparison

<syntaxhighlight lang='kotlin'> data class MyDate(val year: Int, val month: Int, val dayOfMonth: Int) : Comparable<MyDate> {

   override fun compareTo(other: MyDate) = when {
       year != other.year -> year - other.year
       month != other.month -> month - other.month
       else -> dayOfMonth - other.dayOfMonth
   }

}

fun compare(date1: MyDate, date2: MyDate) = date1 < date2 </source>

2 In range

<syntaxhighlight lang='kotlin'> class DateRange(val start: MyDate, val endInclusive: MyDate) {

   operator fun contains(item: MyDate): Boolean = start <= item && item <= endInclusive

}

fun checkInRange(date: MyDate, first: MyDate, last: MyDate): Boolean {

   return date in DateRange(first, last)

} </source>

3 Range to

<syntaxhighlight lang='kotlin'> operator fun MyDate.rangeTo(other: MyDate) = DateRange(this, other)

class DateRange(override val start: MyDate, override val endInclusive: MyDate): ClosedRange<MyDate>

fun checkInRange(date: MyDate, first: MyDate, last: MyDate): Boolean {

   return date in first..last

} </source>

4 For loop

<syntaxhighlight lang='kotlin'> class DateRange(val start: MyDate, val end: MyDate): Iterable<MyDate>{

   override fun iterator(): Iterator<MyDate> = DateIterator(this)

}

class DateIterator(val dateRange:DateRange) : Iterator<MyDate> {

   var current: MyDate = dateRange.start
   override fun next(): MyDate {
       val result = current
       current = current.nextDay()
       return result
   }
   override fun hasNext(): Boolean = current <= dateRange.end

}

fun iterateOverDateRange(firstDate: MyDate, secondDate: MyDate, handler: (MyDate) -> Unit) {

   for (date in firstDate..secondDate) {
       handler(date)
   }

} </source>

5 Operators overloading

<syntaxhighlight lang='kotlin'> import TimeInterval.*

data class MyDate(val year: Int, val month: Int, val dayOfMonth: Int)

enum class TimeInterval { DAY, WEEK, YEAR }

operator fun MyDate.plus(timeInterval: TimeInterval) = addTimeIntervals(timeInterval, 1)

class RepeatedTimeInterval(val timeInterval: TimeInterval, val number: Int) operator fun TimeInterval.times(number: Int) = RepeatedTimeInterval(this, number)

operator fun MyDate.plus(timeIntervals: RepeatedTimeInterval) = addTimeIntervals(timeIntervals.timeInterval, timeIntervals.number)

fun task1(today: MyDate): MyDate {

   return today + YEAR + WEEK

}

fun task2(today: MyDate): MyDate {

   return today + YEAR * 2 + WEEK * 3 + DAY * 5

} </source>

6 Destructuring declarations

<syntaxhighlight lang='kotlin'> data class MyDate(val year: Int, val month: Int, val dayOfMonth: Int)

fun isLeapDay(date: MyDate): Boolean {

   val (year, month, dayOfMonth) = date

   // 29 February of a leap year
   return year % 4 == 0 && month == 2 && dayOfMonth == 29

} </source>

7 Invoke

Kotlin invoke() 문서를 참고하십시오.

<syntaxhighlight lang='kotlin'> class Invokable {

   var numberOfInvocations: Int = 0
       private set
   operator fun invoke(): Invokable {
       numberOfInvocations++
       return this
   }

}

fun invokeTwice(invokable: Invokable) = invokable()() </source>