PragProg Customers

Programming Kotlin: should "variance" be "invariance"? (page 94)

vlastimir

vlastimir

Programming Kotlin: should "variance" be "invariance"? (page 94)

Title: Programming Kotlin: (page 94)
There is sentence:
In this section we’ll first review type variance, which is available in Java.
Should not it be:
In this section we’ll first review type invariance, which is available in Java.
Please tell me, if I am wrong I have deep misunderstanding of Java generics. Thank you.

1 comment
#errata/book-programming-kotlin
1 856 1

First Post!

venkats

venkats

Author of Programming Kotlin, Rediscovering JavaScript (and 6 other titles)

Thank you for the question, Vlastimir.

Languages offer different variance for type in different situations, invariance, covariance, or contravariance. In the section we are going to review the type variance options.

Hope that helps.

Regards,

Venkat

Post #2

Where Next?

View thread on forum
View Programming Kotlin's book portal
Post errata for this book
Post a suggestion for this book
Post a question about this book
Post a review about this book
Home PragProg Customers
#errata/book-programming-kotlin
1 856 1
Last post

Popular Pragmatic Bookshelf topics Top

jimmykiang
PragProg Customers

Distributed Services With Go - Agent_test.go error line 77
This test is broken right out of the box… — FAIL: TestAgent (7.82s) agent_test.go:77: Error Trace: agent_test.go:77 agent_test.go:...
#errata/book-distributed-services-with-go
4 1547 7
New
ianwillie
PragProg Customers

Build Websites with Hugo: Code will not run in a working Hugo setup
Hello Brian, I have some problems with running the code in your book. I like the style of the book very much and I have learnt a lot as...
#question/book-build-websites-with-hugo
0 1500 3
New
simonpeter
PragProg Customers

Web Development with Clojure, Third Edition: (create-migration "guestbook") not working (page 9)
When I try the command to create a pair of migration files I get an error. user=> (create-migration "guestbook") Execution error (Ill...
#errata/book-web-development-with-clojure-third-edition
5 1779 4
New
lirux
PragProg Customers

The Ray Tracer Challenge: "Computing the normal on a transformed sphere" ebook test
Hi Jamis, I think there’s an issue with a test on chapter 6. I own the ebook, version P1.0 Feb. 2019. This test doesn’t pass for me: ...
#errata/book-the-ray-tracer-challenge
10 1451 5
New
jskubick
PragProg Customers

Kotlin and Android Development featuring Jetpack: $kotlin_version ? (page 8)
I’m running Android Studio “Arctic Fox” 2020.3.1 Patch 2, and I’m embarrassed to admit that I only made it to page 8 before running into ...
#errata/book-kotlin-and-android-development-featuring-jetpack
0 1696 3
New
brunogirin
PragProg Customers

Python Testing with pytest, Second Edition: error when installing editable package (page 178)
When installing Cards as an editable package, I get the following error: ERROR: File “setup.py” not found. Directory cannot be installe...
#errata/book-python-testing-with-pytest-second-edition
0 1727 1
New
hazardco
PragProg Customers

Agile Web Development with Rails 7: Example code does not work delete method (page 78)
On page 78 the following code appears: <%= link_to ‘Destroy’, product, class: ‘hover:underline’, method: :delete, data: { confirm...
#suggestion/book-agile-web-development-with-rails-7
1 1265 2
New
rainforest
PragProg Customers

Real-Time Phoenix: use PubSub with implementation of Phoenix.Socket.Transport rather than channels (page 37)
Hi, I’ve got a question about the implementation of PubSub when using a Phoenix.Socket.Transport behaviour rather than channels. Before ...
#question/book-real-time-phoenix#websockets#phoenixsocket#pubsub
0 1506 3
New
tkhobbes
PragProg Customers

Modern Front-End Development for Rails - application does not start after run bin/setup (page xviii)
After some hassle, I was able to finally run bin/setup, now I have started the rails server but I get this error message right when I vis...
#errata/book-modern-front-end-development-for-rails
0 1460 5
New
mcpierce
PragProg Customers

Kotlin and Android Development featuring Jetpack: Unique constraint error when running chapter 5 code changes
@mfazio23 I’ve applied the changes from Chapter 5 of the book and everything builds correctly and runs. But, when I try to start a game,...
/book-kotlin-and-android-development-featuring-jetpack
0 1160 10
New

Other popular topics Top

AstonJ
General Dev>Dev Chat

Best chairs for developers?
What chair do you have while working… and why? Is there a ‘best’ type of chair or working position for developers?
#workspace#opinions
74 4882 41
New
Exadra37
General Dev>Hardware

What monitor(s) do you have for programming?
Please tell us what is your preferred monitor setup for programming(not gaming) and why you have chosen it. Does your monitor have eye p...
#monitors#coding#programming#development
227 8684 88
New
PragmaticBookshelf
Game Dev>Learning Resources

Apple Game Frameworks and Technologies
Design and develop sophisticated 2D games that are as much fun to make as they are to play. From particle effects and pathfinding to soci...
pragprog.com
#pragprog#ios#game-dev#macos/swift#published-book#apple/book-apple-game-frameworks-and-technologies
30 3963 10
New
brentjanderson
General Dev>Hardware

Moonlander Keyboard (Mechanical) (Ergonomic) (Split) (Ortholinear)
Bought the Moonlander mechanical keyboard. Cherry Brown MX switches. Arms and wrists have been hurting enough that it’s time I did someth...
#hardware/keyboards#moonlander#mechanical-keyboards#ortholinear#ergonomic
212 15008 90
New
AstonJ
General Dev>Hardware

Keyboard thock (sound)
I’ve been hearing quite a lot of comments relating to the sound of a keyboard, with one of the most desirable of these called ‘thock’, he...
/keyboards#mechanical-keyboards
14 7927 8
New
Rainer
General Dev>Dev Chat

Do you have any (non-dev) hobbies?
Not sure if following fits exactly this thread, or if we should have a hobby thread… For many years I’m designing and building model air...
#community
200 3586 78
New
Exadra37
Linux>Questions

What is the most minimalist Linux server distro?
I am asking for any distro that only has the bare-bones to be able to get a shell in the server and then just install the packages as we ...
#linux#servers
66 21694 24
New
PragmaticBookshelf
Backend>Learning Resources

Python Testing with pytest, Second Edition
Create efficient, elegant software tests in pytest, Python's most powerful testing framework. Brian Okken @brianokken Edited by Kat...
pragprog.com
#pragprog/python#published-book/book-python-testing-with-pytest-second-edition
16 3580 4
New
rustkas
Backend>Chat

Using Regular Expressions in Erlang
Intensively researching Erlang books and additional resources on it, I have found that the topic of using Regular Expressions is either c...
/erlang#regular-expressions
91 5152 43
New
PragmaticBookshelf
Community>In The Spotlight

Spotlight: Peter Ullrich (Author) Interview and AMA!
Author Spotlight: Peter Ullrich @PJUllrich Data is at the core of every business, but it is useless if nobody can access and analyze ...
/elixir/phoenix/book-building-table-views-with-phoenix-liveview
72 3959 21
New
Back to top

Latest in Programming Kotlin

Programming Kotlin Portal ❯

PragProg Customers

Pragmatic Bookshelf PragProg Customers ❯

Latest on Devtalk

Devtalk ❯

We ❤️ helpful members!

We reward our most helpful members via our MOTM scheme - by giving away a whopping 25 books per year!

Member of the Month

Devtalk Sponsors

Pragmatic Bookshelf

Practical resources that improve the lives of professional developers.

Erlang Solutions

We build trusted fault-tolerant systems that scale to billions of users.

Honeybadger

Real-time error tracking, performance insights, and observability for devs.

Manning Publications

Develop your skills with books, videos, and courses.

AppSignal

Catch errors, track performance, monitor hosts and more.

WyeWorks

Enabling companies to succeed by building software people love.

Pragmatic Studio

Courses that move you from confusion to "Aha, now I get it!"

View all our sponsors ❯

Categories:

Sub Categories:

Popular Portals

Devtalk Sponsors

Pragmatic Bookshelf

Practical resources that improve the lives of professional developers.

Erlang Solutions

We build trusted fault-tolerant systems that scale to billions of users.

Honeybadger

Real-time error tracking, performance insights, and observability for devs.

Manning Publications

Develop your skills with books, videos, and courses.

AppSignal

Catch errors, track performance, monitor hosts and more.

WyeWorks

Enabling companies to succeed by building software people love.

Pragmatic Studio

Courses that move you from confusion to "Aha, now I get it!"

View all our sponsors ❯

We're in Beta

About us Mission Statement See our Roadmap