Kotlin Introduction
- Kotlin Hello World
- Kotlin Data Types
- Kotlin Operators
- Kotlin Type Conversion
- Kotlin Expression & Statement
- Kotlin Comments
- Kotlin Input/Output
Kotlin Flow Control
- Kotlin if expression
- Kotlin when Expression
- Kotlin while Loop
- Kotlin for Loop
- Kotlin break
- Kotlin continue
Kotlin Functions
Kotlin OOP
- Kotlin Class and Objects
- Kotlin Constructors
- Kotlin Getters and Setters
- Kotlin Inheritance
- Kotlin Visibility Modifiers
- Kotlin Abstract Class
- Kotlin Interfaces
- Kotlin Nested and Inner Classes
- Kotlin Data Class
- Kotlin Sealed Class
- Kotlin Object
- Kotlin Companion Objects
- Kotlin Extension Function
- Kotlin Operator Overloading
In this article, you will learn about operator overloading (define how operator works for user defined types like objects) with the help of examples.
When you use operator in Kotlin, it’s corresponding member function is called. For example, expression a+b transforms to a.plus(b) under the hood.
fun main(args: Array<String>) {
val a = 5
val b = 10
print(a.plus(b)) // print(a+b)
}
When you run the program, the output will be:
15
In fact, plus() function is overloaded to work with various Kotlin basic types and String.
// + operator for basic types operator fun plus(other: Byte): Int operator fun plus(other: Short): Int operator fun plus(other: Int): Int operator fun plus(other: Long): Long operator fun plus(other: Float): Float operator fun plus(other: Double): Double // for string concatenation operator fun String?.plus(other: Any?): String
You can also define how operator works for objects by overloading its corresponding function. For example, you need define how + operator works for objects by overloading plus() function.
Example: Overloading + Operator
fun main(args: Array<String>) {
val p1 = Point(3, -8)
val p2 = Point(2, 9)
var sum = Point()
sum = p1 + p2
println("sum = (${sum.x}, ${sum.y})")
}
class Point(val x: Int = 0, val y: Int = 10) {
// overloading plus function
operator fun plus(p: Point) : Point {
return Point(x + p.x, y + p.y)
}
}
When you run the program, the output will be:
sum = (5, 1)
Here, the plus() function is marked with operator keyword to tell compiler that + operator is being overloaded.
The expression p1 + p2 is transformed to p1.plus(p2) under the hood.
Example: — Operator Overloading
In this example, you will learn to overload -- operator. The expression --a is transformed to a.dec() under the hood.
The dec() member function doesn’t take any arguments.
fun main(args: Array<String>) {
var point = Point(3, -8)
--point
println("point = (${point.x}, ${point.y})")
}
class Point(var x: Int = 0, var y: Int = 10) {
operator fun dec() = Point(--x, --y)
}
When you run the program, the ouput will be:
point = (2, -9)
Remember that,
operator fun dec() = Point(--x, --y)
is equivalent to
operator fun dec(): Point {
return Point(--x, --y)
}
Few Important Points
1. When you overload operators, you should try to maintain the original spirit of the operator. For example,
fun main(args: Array<String>) {
val p1 = Point(3, -8)
val p2 = Point(2, 9)
var sum = Point()
sum = p1 + p2
println("sum = (${sum.x}, ${sum.y})")
}
class Point(val x: Int = 0, val y: Int = 10) {
// overloading plus function
operator fun plus(p: Point) = Point(x - p.x, y - p.y)
}
Although the program above is technically correct, we have used + operator to subtract corresponding properties of two objects which made the program confusing.
2. Unlike languages like Scala, only a specific set of operators can be overloaded in Kotlin. Visit the page to learn about operators that can be overloaded in Kotlin and their corresponding member functions.
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