Implement higher order functions and lambda

Question

i try to add to the higher order function an lambda expression. but my question is : how can I implement the forEach function, which each element from the list with the passed Function action calls?

import java.lang.IndexOutOfBoundsException

    class LinkedList <T> {
        data class Node<T>(val data: T, var next: Node<T>?)

        private var first: Node<T>? = null


        fun addFirst(data: T) {
            val newNode = Node(data, first)
            first = newNode
        }

        fun isEmpty() = first == null

         fun clear(): Any {
           return LinkedList<T>().clear()
        }

        fun get(index: Int): Any {
            var position = 0
            var runPointer = first
            while (runPointer != null && position != index) {
                position += 1
                runPointer = runPointer.next
            }
            return runPointer?.data ?: throw IndexOutOfBoundsException()
        }

         
         
        fun forEach(action: (T) -> Unit) {  
            ...

        }
    }

Same way you implemented get but calling action on runPointer.data — al3c
– al3c, Commented May 12, 2021 at 16:26
I agree with @al3c, you just need to call action on each of the runPointer.data you encounter while you loop. Also, what is clear()'s contract here? It seems to be really really weird: it returns an empty list but doesn't do anything with this list. — Joffrey
– Joffrey, Commented May 12, 2021 at 17:16
can you show me an example with each of the functions, because it doesn't work for me — adersat
– adersat, Commented May 12, 2021 at 17:38

VaiTon · Accepted Answer · 2021-05-12 18:04:16Z

2

As you are using a first: Node you should do:

fun forEach(action: (T) -> Unit) {
    var p = first
    while (p != null) {
        action(p.data)
        p = p.next
    }
}

answered May 12, 2021 at 18:04

VaiTon

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Comments

Ananiya J. Kesto · Accepted Answer · 2021-05-12 17:12:54Z

0

Well forEach is extension function of Iterrable as in std lib

 fun <T> Iterable<T>.forEach(action: (T) -> Unit): Unit {
    for (element in this) action(element)
}

Source https://github.com/JetBrains/kotlin/blob/master/libraries/stdlib/common/src/generated/_Collections.kt

edited May 12, 2021 at 17:12

answered May 12, 2021 at 16:29

Ananiya J. Kesto

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2 Comments

adersat Over a year ago

ok thanks but how can i do it without the iterable. How should i write it in here fun forEach(action: (T) -> Unit) {

Ananiya J. Kesto Over a year ago

Well you can use it with out Iterrable like fun forEach.. but this is applicable for only LinkedList type in other word the variable you call must be a child of the super class

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