Covariance & Contravariance in PHP – Full PHP 8 Tutorial

Covariant & Contravariant types are the topic that boggles our minds sometimes. In this video, I try to explain it in more detail the way I wish someone explained it to me when I was learning it because this is one of the topics that was somewhat difficult to grasp in the beginning.

SOME OF THE WAYS YOU CAN SUPPORT THE CHANNEL
👍 Smash the like button
🤝 Subscribe to the channel & turn the notifications on
💬 Post comments, any feedback is greatly appreciated
⭐ Become a Patreon: https://www.patreon.com/programwithgio
THANK YOU!

🛠️ TOOLS & SERVICES I USE
Digital Ocean Hosting – Get 100$ credit – https://m.do.co/c/38b935ad74e5
Domains on Namecheap – https://namecheap.pxf.io/rnRjdQ
Envato Elements – https://1.envato.market/c/2937311/298927/4662
Adobe Photoshop & Premiere – https://clk.tradedoubler.com/click?p=264355&a=3250276

COURSE PLAYLIST

RESOURCES
Docs – https://www.php.net/manual/en/language.oop5.variance.php
RFC that added covariant return & contravariant parameter type support – https://wiki.php.net/rfc/covariant-returns-and-contravariant-parameters
Great article by Nikita Popov about type variance – https://www.npopov.com/2021/11/08/Type-variance-in-PHP.html
Another great article about LSP & type safety – https://stitcher.io/blog/liskov-and-type-safety
Online PHP Shell – https://3v4l.org/

TABLE OF CONTENTS
00:00 – Covariant & Contravariant Types
01:40 – Return Type Covariance Example
04:38 – Paramter Type Contravariance Example
06:39 – Testing Covariance & Contravariance In PHP 7.3
08:06 – Covariant Parameter & Contravariant Return Type Support?
10:16 – Covariance & Contravariance With Union & Intersection Types
11:48 – Liskov Substitution Principle (LSP)

** Affiliate Disclaimer: Some of the above links may be affiliate links, which may generate me a sales commission at no additional cost to you.