Operator Function Overloading in Kotlin

Introduction

Operator Function Overloading is a fundamental concept every Kotlin developer should understand. This topic is part of the Kotlin learning path.

Kotlin lets you define how custom types respond to operators like + or ==. In this tutorial you will learn the syntax, walk through a complete example program, study the sample output, and review best practices so you can apply the concept confidently in your own projects.

Definition

• Kotlin lets you define how custom types respond to operators like + or ==.
• Mark a function with operator and use a supported operator name.
• Common overloads include plus, minus, equals, and get for index access.

Syntax

operator fun plus(other: Point): Point

Operator Function Overloading in Kotlin Example Program in Kotlin

data class Point(val x: Int, val y: Int) {
    operator fun plus(other: Point) = Point(x + other.x, y + other.y)
}

fun main() {
    val p1 = Point(1, 2)
    val p2 = Point(3, 4)
    val sum = p1 + p2
    println("Sum point: (${sum.x}, ${sum.y})")
}

Sample Output

Sum point: (4, 6)

When to use

Reach for operator function overloading when the problem you are solving matches the patterns described in the definition above.

How it works

1. The program starts with a main function — the entry point that runs when you execute the file.

2. Kotlin lets you define how custom types respond to operators like + or ==.

3. Run the program in IntelliJ IDEA, Android Studio, or with the Kotlin command-line compiler (kotlinc / kotlin). Compare your console output with the sample output shown below.

Best Practices

Common Mistakes

Key Points

• Kotlin lets you define how custom types respond to operators like + or ==.
• Mark a function with operator and use a supported operator name.
• Common overloads include plus, minus, equals, and get for index access.
• Test the example locally and verify the output matches the sample.
• Experiment by changing input values to see how behaviour changes.

Notes

• Semicolons at the end of statements are optional in Kotlin.