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swiftoperator-overloadingsubscript-operator

Swift operator `subscript` []

I am beginner with the Swift having no advance knowledge with operators.

I have the following class

class Container {
   var list: [Any] = [];
}

I want to implement the operator subscript [] in order to access the data from list.

I need something like this: 

var data: Container = Container()
var value = data[5]
// also    
data[5] = 5

Also I want to be able to write something like this:

data[1][2]

Is it possible considering that element 1 from Container is an array?

Thanx for help.

Solution

  • It looks like there are 2 questions here.

    1. How can I enable subscripting on my own custom class?

    To enable subscripting on your class Container you need to implement the subscript computed property like this.

    class Container {
    private var list : [Any] = [] // I made this private

    subscript(index:Int) -> Any {
        get {
            return list[index]
        }
        set(newElm) {
            list.insert(newElm, atIndex: index)
        }
    }
}

    Now you can use it this way.

    var container = Container()
container[0] = "Star Trek"
container[1] = "Star Trek TNG"
container[2] = "Star Trek DS9"
container[3] = "Star Trek VOY"

container[1] // "Star Trek TNG"

    2. Can I access one element of Container that supports subscripting writing something like data[1][2]?

    If we use your example no, you cannot. Because data[1] returns something of type Any. And you cannot subscript Any.

    But if you add a cast it becomes possible

    var container = Container()
container[0] = ["Enterprise", "Defiant", "Voyager"]
(container[0] as! [String])[2] // > "Voyager"