Functional Kotlin

Side effects

In a computer program, when a function modifies any object/data outside its own scope, that is called a side effect. For instance, we often write functions that modify a global or static property, modify one of its arguments, raise an exception, write data to display or file, or even call another function which has a side effect.

For example, have a look at the following program:

class Calc { 
    var a:Int=0 
    var b:Int=0 
    fun addNumbers(a:Int = this.a,b:Int = this.b):Int {  
        this.a = a 
        this.b = b 
        return a+b 
    } 
} 
fun main(args: Array<String>) { 
    val calc = Calc() 
    println("Result is ${calc.addNumbers(10,15)}") 
} 

The preceding program is a simple object-oriented program. However, it contains side effects. The addNumbers() function modifies ...