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[ | ]

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

2 In range[ | ]

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)
}

MyDate.kt

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
    }
}

3 Range to[ | ]

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
}

MyDate.kt

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
    }
}

4 For loop[ | ]

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)
    }
}

MyDate.kt

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
    }
}

operator fun MyDate.rangeTo(other: MyDate) = DateRange(this, other)

DateUtil.kt

import java.util.Calendar

fun MyDate.nextDay() = addTimeIntervals(TimeInterval.DAY, 1)

enum class TimeInterval {
    DAY,
    WEEK,
    YEAR
}

fun MyDate.addTimeIntervals(timeInterval: TimeInterval, number: Int): MyDate {
    val c = Calendar.getInstance()
    c.set(year, month, dayOfMonth)
    when (timeInterval) {
        TimeInterval.DAY -> c.add(Calendar.DAY_OF_MONTH, number)
        TimeInterval.WEEK -> c.add(Calendar.WEEK_OF_MONTH, number)
        TimeInterval.YEAR -> c.add(Calendar.YEAR, number)
    }
    return MyDate(c.get(Calendar.YEAR), c.get(Calendar.MONTH), c.get(Calendar.DATE))
}

5 Operators overloading[ | ]

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
}

DateUtil.kt

import java.util.Calendar

fun MyDate.addTimeIntervals(timeInterval: TimeInterval, number: Int): MyDate {
    val c = Calendar.getInstance()
    c.set(year, month, dayOfMonth)
    when (timeInterval) {
        TimeInterval.DAY -> c.add(Calendar.DAY_OF_MONTH, number)
        TimeInterval.WEEK -> c.add(Calendar.WEEK_OF_MONTH, number)
        TimeInterval.YEAR -> c.add(Calendar.YEAR, number)
    }
    return MyDate(c.get(Calendar.YEAR), c.get(Calendar.MONTH), c.get(Calendar.DATE))
}

6 Destructuring declarations[ | ]

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
}

7 Invoke[ | ]

Kotlin invoke() 문서를 참고하십시오.

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

fun invokeTwice(invokable: Invokable) = invokable()()