Скачать или смотреть Demystifying Co, Contra, In Kotlin Variance Notations

This video is about Variance and understanding the way it works with keywords out/in and of course nothing. Let's have a look!. We'll talk about covariance, variance and contravariance!

It's been a long time since I've posted a long on this channel. As you know I made a kind of promise that I would be making a lot more long-form videos. However, I still needed to learn a lot about filming, lighting, video resolution, and the capacity of my devices, which isn't great.

This video took a long time to film and a lot more to edit and correct some mistakes I made. I am much more comfortable with the camera than I have ever been and I hope you enjoy this video.

This video is about the keywords in and out in Kotlin are translated to declaring contravariant and covariant generic types. In the live-coding example of this video, we are going to have a look at an example with a single concrete class definition. The supporting repo on Git Hub has a new name. I have given it a new name to reflect better what the repo is about and how it started. Its new name is asnsei-the-right-waf and you can find it here:

Asnsei The Right Waf - https://github.com/jesperancinha/asns...

My apologies because I didn't take notice of a few mistakes I made implementing the getBox method in both Kotlin and Java versions during filming. It is not important for the tutorial itself but it is better to keep your IDE open to read the code while watching the film. Have a look at the source code first, please!

If you have suggestions on how can I make future videos better please feel free to leave a comment. Thank you!

---

Chapters

00:00 Introduction
00:34 Repository introduction
04:01 The example
04:45 The UML Explained
05:15 Live coding
07:40 Building the service with a concrete class
11:43 Creating the service instances
12:24 Creating generic functions
13:02 Gradle Issue (Fast Forward)
13:11 Resuming running application
15:32 Using In and Out for the first time
17:05 Fixing In / Out compiler errors
19:33 "@UnsafeVariance"
20:37 Video Interruption - Correcting the function calls (The getBox method has been fixed in the source code)
23:48 Change of plans. Services are created on the basis of temperature
33:43 The same implementation in Java
44:49 Java folder issue by default in Gradle (Fast Forward)
44:59 Resuming reflections between Java and Kotlin
45:21 Video interruption - Fast scroll on Kotlin Example with abstractions
46:30 Where, how, when, how come In and Out?
47:05 Showing off credentials
47:15 Resuming philosophical discussion
49:09 Project location (It has changed before the video was published!)
49:26 Goodbye and see you in the next video!
---

Slides:

Demystifying Co, Contra, In Kotlin on Scribd: https://www.scribd.com/presentation/7...
Demystifying Co, Contra, In Kotlin on slide-share: https://www.slideshare.net/slideshows...


---

Videos mentioned:

Can You Ace This Covariance Challenge? (JQ07) -    • Can You Ace This Covariance Challenge? Fin...  
UnsafeVariance uncovered! (JA07) -    • UnsafeVariance annotation uncovered! (JA07...  

---

And while you are reading this, if you are interested in knowing about data classes in Kotlin and on the other hand about records and Lombok in Java, please have a look at almost all my repos to see the differences and learn how and where to use them, but for now, I hope you enjoy this video!

My best repos to learn about records are:

JEOrg Spring Test Drives - https://github.com/jesperancinha/jeor...
JEOrg Spring Master Test Drives - https://github.com/jesperancinha/jeor...

And since most of my repos are in Kotlin and can give one example:

Concert Demos Root on GitHub - https://github.com/jesperancinha/conc...

---

All my work and personal interests are discoverable on different sites:

JESC (João Esperancinha Software Creations) -    / @joaoesperancinha  
JACE (João Arts & Crafts Esperancinha)-    / @joaoesperancinhacjace  
JECI (João Esperancinha Cooking Ideas)    / @joaoesperancinhaci  
JEBotanical (João Esperancinha Botanical)   / @joaoesperancinhabotanical  
My Website - https://joaofilipesabinoesperancinha.nl/
Credly - https://www.credly.com/users/joao-esp...
Pinterest -   / jesperancinha  
Instagram -   / joaofisaes  
Facebook -   / joaofisaes  
Spotify - https://open.spotify.com/user/jlnozkc...

---

If you want to discover more about my open-source work please visit me on GitHub at:

GitHub - https://github.com/jesperancinha

And until the next video,

Keep it graceful and stay sharp!