What is operator overloading and how to use it?

Operator overloading in Kotlin allows you to define or override the behavior of standard operators (e.g., +, -, *, /) for user-defined data types.

It is used by defining special member functions or extension functions with fixed names, marked with the keyword operator.

Functions for operator overloading:

Operator	Function name
+	plus
-	minus
*	times
/	div
%	rem, mod
..	rangeTo
in	contains
==	equals
!=	equals (inverted result)
<	compareTo
>	compareTo
<=	compareTo
>=	compareTo
[]	get, set
()	invoke
a += b	plusAssign
a -= b	minusAssign
a *= b	timesAssign
a /= b	divAssign
a %= b	remAssign, modAssign
+a	unaryPlus
-a	unaryMinus
!a	not
a++, ++a	inc
a--, --a	dec

Example of overloading the + operator for the Vector class:

data class Vector(val x: Int, val y: Int) {
    // Overloading the "+" operator
    operator fun plus(other: Vector): Vector {
        return Vector(x + other.x, y + other.y)
    }
}

fun main() {
    val v1 = Vector(1, 2)
    val v2 = Vector(3, 4)
    val v3 = v1 + v2 // Using the overloaded operator
    println(v3) // Output: Vector(x=4, y=6)
}

Example of overloading the [] (get) operator for a collection class:

class MyContainer(private val elements: List<String>) {
    // Overloading the "[]" (get) operator
    operator fun get(index: Int): String {
        return elements[index]
    }
}

fun main() {
    val container = MyContainer(listOf("A", "B", "C"))
    val element = container[1] // Using the overloaded operator
    println(element) // Output: B
}