# Errata on chapter 4

**URL:** <https://forums.kodeco.com/t/errata-on-chapter-4/118331>\
**Category:** Data Structures and Algorithms in Kotlin\
**Created:** [August 25, 2020, 12:22pm UTC](https://forums.kodeco.com/t/errata-on-chapter-4/118331 "2020-08-25T12:22:34Z")\
**Posts on this page:** 3\
**Page:** 1

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**Author:** ![arrmixer](https://assets.chunter.kodeco.com/user_avatar/forums.kodeco.com/arrmixer/32/108693_2.png) [@arrmixer](https://forums.kodeco.com/u/arrmixer)\
**Post date:** [August 25, 2020, 12:22pm UTC](https://forums.kodeco.com/t/errata-on-chapter-4/118331/1 "2020-08-25T12:22:35Z")

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There is a mistake in this chapter where the reader is asked to add a class to the same stack.kt file where the inference is… this is fine except the implementation code is wrong:  
class Stack() {  
private val storage = arrayListOf()

it should be:  
class StackImpl : Stack {  
private val storage = arrayListOf()

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**Author:** ![gdelarosa](https://assets.chunter.kodeco.com/user_avatar/forums.kodeco.com/gdelarosa/32/109063_2.png) [@gdelarosa](https://forums.kodeco.com/u/gdelarosa)\
**Post date:** [August 25, 2020, 3:32pm UTC](https://forums.kodeco.com/t/errata-on-chapter-4/118331/2 "2020-08-25T15:32:10Z")

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Thank you for sharing your implementation @arrmixer!

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<div class="post-metadata">

**Author:** ![shogunkaramazov](https://assets.chunter.kodeco.com/user_avatar/forums.kodeco.com/shogunkaramazov/32/108826_2.png) [@shogunkaramazov](https://forums.kodeco.com/u/shogunkaramazov)\
**Post date:** [April 8, 2021, 3:45am UTC](https://forums.kodeco.com/t/errata-on-chapter-4/118331/3 "2021-04-08T03:45:28Z")

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@mateisuica Can you please help with this when you get a chance? Thank you - much appreciated! :]