Merge pull request #5800 from alimate/BAEL-2375

BAEL-2375: Operator Overloading in Kotlin

core-kotlin/src/main/kotlin/com/baeldung/operators/Money.kt

@@ -0,0 +1,31 @@
+package com.baeldung.operators
+
+import java.math.BigDecimal
+
+enum class Currency {
+    DOLLARS, EURO
+}
+
+class Money(val amount: BigDecimal, val currency: Currency) : Comparable<Money> {
+
+    override fun compareTo(other: Money): Int =
+            convert(Currency.DOLLARS).compareTo(other.convert(Currency.DOLLARS))
+
+    fun convert(currency: Currency): BigDecimal = TODO()
+
+    override fun equals(other: Any?): Boolean {
+        if (this === other) return true
+        if (other !is Money) return false
+
+        if (amount != other.amount) return false
+        if (currency != other.currency) return false
+
+        return true
+    }
+
+    override fun hashCode(): Int {
+        var result = amount.hashCode()
+        result = 31 * result + currency.hashCode()
+        return result
+    }
+}

core-kotlin/src/main/kotlin/com/baeldung/operators/Page.kt

@@ -0,0 +1,16 @@
+package com.baeldung.operators
+
+interface Page<T> {
+    fun pageNumber(): Int
+    fun pageSize(): Int
+    fun elements(): MutableList<T>
+}
+
+operator fun <T> Page<T>.get(index: Int): T = elements()[index]
+operator fun <T> Page<T>.get(start: Int, endExclusive: Int): List<T> = elements().subList(start, endExclusive)
+operator fun <T> Page<T>.set(index: Int, value: T) {
+    elements()[index] = value
+}
+
+operator fun <T> Page<T>.contains(element: T): Boolean = element in elements()
+operator fun <T> Page<T>.iterator() = elements().iterator()

core-kotlin/src/main/kotlin/com/baeldung/operators/Point.kt

@@ -0,0 +1,31 @@
+package com.baeldung.operators
+
+data class Point(val x: Int, val y: Int)
+
+operator fun Point.unaryMinus() = Point(-x, -y)
+operator fun Point.not() = Point(y, x)
+operator fun Point.inc() = Point(x + 1, y + 1)
+operator fun Point.dec() = Point(x - 1, y - 1)
+
+operator fun Point.plus(other: Point): Point = Point(x + other.x, y + other.y)
+operator fun Point.minus(other: Point): Point = Point(x - other.x, y - other.y)
+operator fun Point.times(other: Point): Point = Point(x * other.x, y * other.y)
+operator fun Point.div(other: Point): Point = Point(x / other.x, y / other.y)
+operator fun Point.rem(other: Point): Point = Point(x % other.x, y % other.y)
+operator fun Point.times(factor: Int): Point = Point(x * factor, y * factor)
+operator fun Int.times(point: Point): Point = Point(point.x * this, point.y * this)
+
+class Shape {
+    val points = mutableListOf<Point>()
+
+    operator fun Point.unaryPlus() {
+        points.add(this)
+    }
+}
+
+fun shape(init: Shape.() -> Unit): Shape {
+    val shape = Shape()
+    shape.init()
+
+    return shape
+}

core-kotlin/src/main/kotlin/com/baeldung/operators/Utils.kt

@@ -0,0 +1,8 @@
+package com.baeldung.operators
+
+import java.math.BigInteger
+
+operator fun <T> MutableCollection<T>.plusAssign(element: T) {
+    add(element)
+}
+operator fun BigInteger.plus(other: Int): BigInteger = add(BigInteger("$other"))

core-kotlin/src/test/kotlin/com/baeldung/operators/PageTest.kt

@@ -0,0 +1,28 @@
+package com.baeldung.operators
+
+import org.junit.Test
+import kotlin.test.assertEquals
+import kotlin.test.assertTrue
+
+class PageTest {
+
+    private val page = PageImpl(1, 10, "Java", "Kotlin", "Scala")
+
+    @Test
+    fun `Get convention should work as expected`() {
+        assertEquals(page[1], "Kotlin")
+        assertEquals(page[1, 3], listOf("Kotlin", "Scala"))
+    }
+
+    @Test
+    fun `In convention should work on a page as expected`() {
+        assertTrue("Kotlin" in page)
+    }
+
+}
+
+private class PageImpl<T>(val page: Int, val size: Int, vararg val elements: T) : Page<T> {
+    override fun pageNumber(): Int = page
+    override fun pageSize(): Int = size
+    override fun elements(): MutableList<T> = mutableListOf(*elements)
+}

core-kotlin/src/test/kotlin/com/baeldung/operators/PointTest.kt

@@ -0,0 +1,48 @@
+package com.baeldung.operators
+
+import org.junit.Test
+import kotlin.test.assertEquals
+import kotlin.test.assertTrue
+
+class PointTest {
+
+    private val p1 = Point(1, 2)
+    private val p2 = Point(2, 3)
+
+    @Test
+    fun `We should be able to add two points together using +`() {
+        assertEquals(p1 + p2, Point(3, 5))
+    }
+
+    @Test
+    fun `We shoud be able to subtract one point from another using -`() {
+        assertEquals(p1 - p2, Point(-1, -1))
+    }
+
+    @Test
+    fun `We should be able to multiply two points together with *`() {
+        assertEquals(p1 * p2, Point(2, 6))
+    }
+
+    @Test
+    fun `We should be able to divide one point by another`() {
+        assertEquals(p1 / p2, Point(0, 0))
+    }
+
+    @Test
+    fun `We should be able to scale a point by an integral factor`() {
+        assertEquals(p1 * 2, Point(2, 4))
+        assertEquals(2 * p1, Point(2, 4))
+    }
+
+    @Test
+    fun `We should be able to add points to an empty shape`() {
+        val line = shape {
+            +Point(0, 0)
+            +Point(1, 3)
+        }
+
+        assertTrue(Point(0, 0) in line.points)
+        assertTrue(Point(1, 3) in line.points)
+    }
+}

core-kotlin/src/test/kotlin/com/baeldung/operators/UtilsTest.kt

@@ -0,0 +1,13 @@
+package com.baeldung.operators
+
+import java.math.BigInteger
+import org.junit.Test
+import kotlin.test.assertEquals
+
+class UtilsTest {
+
+    @Test
+    fun `We should be able to add an int value to an existing BigInteger using +`() {
+        assertEquals(BigInteger.ZERO + 1, BigInteger.ONE)
+    }
+}