Added the codes used for operator overloading article

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

@@ -0,0 +1,27 @@
+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 +1,14 @@
+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 +1,14 @@
+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)

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

@@ -0,0 +1,30 @@
+interface View
+class TextView(val value: String) : View
+class ImageView(val url: String) : View
+
+class UI {
+    private val views = mutableListOf<View>()
+
+    operator fun String.unaryPlus() {
+        views.add(TextView(this))
+    }
+
+    operator fun View.unaryPlus() {
+        views.add(this)
+    }
+}
+
+fun ui(init: UI.() -> Unit): UI {
+    val ui = UI()
+    ui.init()
+
+    return ui
+}
+
+fun main(args: Array<String>) {
+    val header = ui {
+        +ImageView("http://logo.com")
+        +"Brand name"
+        +"Brand description"
+    }
+}

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

@@ -0,0 +1,4 @@
+operator fun <T> MutableCollection<T>.plusAssign(element: T) {
+    add(element)
+}
+operator fun BigInteger.plus(other: Int): BigInteger = add(BigInteger("$other"))