Square bracket operator with zero arguments

1

In Scala we can overload the index operator `()` with zero arguments. This is used for instance for the `Signal` and `Var` classes in the Coursera course "Principles of Reactive Programming".

In Kotlin I’d like to have a shorter syntax for foo.value. It would be nice to be able to use foo[] to get and set foo.value.

data class Box<T>(var value: T) {
    public fun get(): T { return this.value }
    public fun set(value: T) { this.value = value }
}



fun main(args: Array<String>) {

  val foo = Box(10)

  println(foo)       // error: expecting an index element

  foo = 12           // error: expecting an index element

  println(foo)       // error: expecting an index element

}

Relevant documentation: http://kotlinlang.org/docs/reference/operator-overloading.html

2

Please use the same "()" operator (invoke) as in Scala.

3

Thanks! Invoke with `()` looks even better. Is there a way to write `foo() = 12`? 

data class Box<T>(var value: T) {
    public fun invoke(): T { return this.value }
    public fun invoke(value: T) { this.value = value }
    public fun set(value: T) { this.value = value }
}

fun main(args: Array<String>) {

  val foo = Box(10)


  // get

    println(foo())


  // set

    foo(12)

  foo() = 12 // error: variable expected

    foo set 12

}


The only way I found so far is to misuse compareTo() in order to write foo() &lt;= 12 instead of foo() = 12. One downside is, that I have to return Box&lt;T&gt; instead of T.

data class Box<T>(var value: T) {
    public fun invoke(): Box<T> { return this }
    public fun invoke(value: T) { this.value = value }
    public fun compareTo(value: T): Int { invoke(value); return 0 }
}

fun main(args: Array<String>) {

  val foo = Box(10)


  println(foo()) // Box(value=10)

    foo() <= 12

    println(foo()) // Box(value=12)

}

4

No, there's no way to support "foo() = x"