Invoke Operator & Operator Overloading in Kotlin

Question

I get to know about the Invoke operator that,

a() is equivalent to a.invoke()

Is there anything more regarding Invoke operator the

Answer 1

The most way to use a invoke operator is use it as a Factory Method, for example:

//          v--- call the invoke(String) operator 
val data1 = Data("1")

//            v--- call the invoke() operator 
val default = Data()

//          v-- call the constructor
val data2 = Data(2)

This is because the companion object is a special object in Kotlin. Indeed, the code Data("1") above is translated to the code as below:

val factory:Data.Companion = Data

//                       v-- the invoke operator is used here
val data1:Data = factory.invoke("1")

---

class Data(val value: Int) {

    companion object {
        const val DEFAULT =-1
        //           v--- factory method
        operator fun invoke(value: String): Data = Data(value.toInt())

        //           v--- overloading invoke operator
        operator fun invoke(): Data = Data(DEFAULT)
    }
}