19 Iterators

Intermediate

To implement iteration functionality for user-defined type, it has to implement Iterable interface.

User-created class that implements Iterable interface. Function iterator, returns an Iterator object, which we have to define specifically for the MyArray class.

MyArrayIter inherits from the abstract Iterator class, and has to implement method next().

Here we have for extended for-loops over our class MyArray. It is only possible because it implements the Iterable interface. We do not have to traverse it in order, we can get creative with the MyArrayIter class.

iterators.cj

class MyArray <: Iterable<Int64> {
    let size = 3
    var arr: Array<Int64>

    public init() {
        arr = Array<Int64>(size, {i: Int64 => i})
    }

    public func iterator(): Iterator<Int64> {
        MyArrayIter(this)
    }
}

class MyArrayIter <: Iterator<Int64> {
    private var idx: Int64
    private let arr_to_iterate: MyArray

    public init(arr: MyArray) {
        idx = 0
        arr_to_iterate = arr
    }

    public func next(): Option<Int64> {
        if (idx < arr_to_iterate.size) {
            idx++
            return Some(arr_to_iterate.arr[idx - 1])
        }
        return None
    }
}

main() {
    let a = MyArray()
    for (i in a) {
        for (p in a) {
            println("${i} ${p}")
        }
    }
}

// Output:
// Numbers in Array: 1 2 3 
// Numbers in ArrayList: 4 5 6 
// Numbers in HashMap: (7,Ali) (8,Isaac) (9,Max) 
// Numbers in HashSet: 10 11 12