CODEWITHSUNDEEP
functionkotlinoperator-overloadingoverloading
Zorgan
Zorgan

Reputation: 9143

Understanding overloading plus function

I'm following a kotlin overloading tutorial here and failing to understand this 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 { 
        return Point(x + p.x, y + p.y) 
    } 
}

When you run the program, the output will be:

sum = (5, 1)

Specifically, the return line: return Point(x + p.x, y + p.y)

How is this line working? Why is it x + p.x - where are those values coming from?

Upvotes: 0

Views: 62

Answers (1)

Sergio
Sergio

Reputation: 30695

You have a class class Point(val x: Int = 0, val y: Int = 10) which has x and y properties. Consider operator fun plus(p: Point) : Point as a simple function of class Point that receives another Point as a parameter, creates another instance of Point adding x and y coordinates of current and another point p and returns it. So in that function you have access to the properties of current instance of Point and another Point instance: x and y.

We can read the expression var sum: Point = p1 + p2 as the following: take p1 as a current instance of Point, add p2 as another instance of Point. In this case plus function is called on the p1 instance with passing p2 as the argument of that function. When the function returns variable sum will refer to the instance of newly created Point.

Upvotes: 1

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