Variance... without Generics! 

Haha, thanks so much, Mike! I do enjoy the challenge!

Thanks so much, Jentaro! Yes, some of the concepts seem a bit counterintuitive at first, but I'm glad this was helpful!

Hey, wow! Thank you so much!

Thank you so much! I'm especially happy to hear that it's helpful for someone who doesn't natively speak English!

Thank you so much! I'm so glad to hear that you've enjoyed the videos and book! I'll keep at it! 👍

You're most welcome! I'm glad you liked it!

Thank you so much - I'm so glad you've found them useful!

Thanks so much! I'll keep at it!

Antonio! Thanks so much! Yes, variance can certainly seem counterintuitive, so I've often had to think twice about it, too. Glad you enjoyed the video!

Haha, thank you! I'm glad you liked it!

Thank you so much! I'm so glad to hear you've enjoyed it!

You're most welcome!

Thank you so much! I'm glad you found it helpful!

You're most welcome! I'm glad you liked it!

I'm so glad it was helpful! And you're most welcome!

Thanks so much, Darwin! I'm glad you liked it!

You're most welcome! I'm glad you found it helpful!

You're most welcome! I'm glad you liked it!

Hey, thank you so much!

Hey Mike, sure thing! Let's say you've got a birthday card that you want to send to your friend. You need to find an envelope receptacle to mail it (i.e., a collection box that accepts envelopes). In this case, the contract you need is that _the receptacle must accept an envelope_. A thin mail slot at an apartment complex would meet your needs - it fulfills the contract, because it accepts an envelope. Now, if you were to go to the post office, they might have a receptacle that's big enough to receive either an envelope _or_ a box package - any kind of mail. That receptacle would _also_ meet your needs, because it still accepts an envelope. Sure, it also happens to accept packages, but that fact is irrelevant to your situation - as long as it accepts an envelope, it meets the contract. Similarly, in Kotlin, you could assign the post office mail receptacle to a variable that's declared as an envelope receptacle, because it can still accept envelopes. --- interface Mail interface Envelope : Mail interface Package : Mail val mailSlot: (Envelope) -> Unit = { /* ... */ } val postOffice: (Mail) -> Unit = { /* ... */ } var envelopeReceptacle: (Envelope) -> Unit envelopeReceptacle = mailSlot // OK - accepts envelopes envelopeReceptacle = postOffice // OK - also still accepts envelopes --- Does that example help to clarify it better?

Thanks @@typealias , I understand the examples but it's also easy to think up examples where this doesn't make sense. You could change the parameter type in the implementation to "Any". Very useful video though - many thanks!

Okay, thanks Mike! If you want, feel free to direct-message me on X or LinkedIn, and I can send you early access to Chapter 19, and see if you still have unanswered questions after reading it. (I'm sure if you'd have some questions, other people would, too!)

I will try to watch the entire video 3-4 times and write notes on it to better understand it.

Wow, watching the video multiple times and taking notes - that's dedication! 👏 The concepts in this video might make more sense for you when chapter 19 comes out, so if it's still not connecting for you after a few times through, don't worry too much!

@@typealias Took 4 more times to rewatch the entire video and understood a lot! Understanding Variance without generics did help to understand how Variance with Generics works! Very nicely explained! Thanks.