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Saved by @CodyyyGardner

It makes me smile every time I notice IGListKit at work in Instagram. We put a lot of work into making and improving it. Proud to see it holding up 4 years later.

🧵 with some memories on how it was built:

 At Instagram, product work slowed around the holidays, so we used the time to pay down tech debt. In winter 2014 I reviewed a +12k line refactor from UITableView to UICollectionView.

We recently dropped iOS 5 so we could use the new 6+ APIs without backwards compatibility.
That review taught me a lot about UICV: data sources should mutate in one place else risk out-of-sync exceptions, the first view layout may reloadData, sticky headers make good perf hard, and many more UICV tidbits
We used reloadData for everything and it worked, for the most part.

Except two things bugged the hell out of me:

1. No animated changes (duh)
2. Images could flicker and the like animation could cancel
I dug into the latter and learned that if you reloadData, every cell on screen gets reused. So even if nothing in the UI changes, you still reuse (or init) cells, bind data, set images, etc. that’s a lot of work!
When you liked a post, we’d call reloadData. Since all cells are replaced: we had to track the liked row, reload, and THEN perform the like animation. 😓

If something triggered another reload after the animation started, the cell cancelled the animation (thus the UI bug)
The image flickering issue was simpler:

When an image cell is reused set the background to grey, async load the image (cache or network), set the image. The async time between reuse and fetch/set from cache is where the flicker came from.
(@ryanolsonk solved the image flicker with an insanely clever “weak image cache” design. It’s a great interview question 😉 )
This all got me thinking: what if we only updated cells when the data changes? This general idea was gaining traction (ahem, React): bind data to views, and diff the data on change to only rebind changed data+views.

Enter UICV performBatchUpdates
Using the principle of only updating the data source in one place, I could diff the from/to data and use UICVs APIs to insert/delete/reload/move. Anything unchanged wouldn’t get touched!

So how the hell do I write a diffing algorithm? I literally had never done this.
I researched several algos: rsync, Myers, react...

I settled on Paul Heckel’s https://t.co/jpxuHNlpXg

Why?

1. It’s output matched UICV’s APIs: inserts, deletes, updates, and moves
2. There were example implementations I could actually understand
A pivotal decision was how we define identity and equality. I wanted to piggy-back off NSObject’s -hash and -isEqual: methods to spare our engineers having to write/understand diffing concepts.
@ryanolsonk convinced me I was wrong bc writing proper -hash is complex https://t.co/4PgDCykAna

Foundation hashes can collide
https://t.co/h9eVHO342U

Or are too basic for diffing
https://t.co/Pp0eVFRS5e https://t.co/ZNPJnXlXa4
We settled on a hybrid API: a protocol with custom identifier and -isEqual: We later scrapped the NSObject tricks as they were easy to abuse & forget, resulting in crashes.
Fun fact: the library was originally called “IGStoryKit” but my director hated that so we renamed it. Glad we did, guess what launched 6 months later? 🤪
Over the next several months, @jesse_squires and I refactored probably 20k lines so that we could run our new infra alongside the old one. This let us safely A/B test performance before rolling out.
We started with single-item feeds but quickly moved to support the main feed. Main feed was scary (we were starting to run ads 😬) but if we could replace feed, then the rest of the app would fall in line.
@ocrickard and I spent a couple months investigating crashes and tuning performance. I learned a lot about ObjC++ during this time (unordered_map was waaaay faster than NSDictionary for our diffing).
We ended up filing 4 UICV radars from all this investigation! Some have been closed

https://t.co/BACvyI2l08+
When everything was fixed, we launched. I spent a year advocating the eng org help refactor and deprecate the old infra. It came down to the profile view. I rolled up my sleeves and did it myself. It was TOUGH

With profile done, I submitted a -12k change to remove the old infra.
From the start we wanted to open source the library. It ended up being a lot of paper work and internal politics, but we did it. Forever grateful to @jesse_squires for setting the project up for success and @mikeyk for having our back.
We started writing the library in late 2015, launched feed summer of 2016, and deleted the old infra in early 2017.

Throughout this the eng team 10x’d and users 4x’d, we launched tons of products (Stories!), IG opened a NY office, UICV got diffable data sources, and more.
After we launched 4y ago I calc’d our diffing algorithm executes over 40,000 times a second. I can’t imagine what that is now!
Building IGListKit was a career’s-worth of learning packed into a couple years.

I’m proud that it’s still powering Instagram today, but I’m looking forward to learning about what replaces it.

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@aetherlev
Great bit of journalism here by Sophia :) fun fact, we had some verrrrry interesting conversations about what exactly the Trump campaign might be doing on TikTok.

So let’s talk about that!


Super glad I could be of help btw :P

Anyhoo: my background = senior web dev, data analysis a specialty, worked in online marketing/advertising a while back

You’ve got this big TikTok account that’s ostensibly all volunteer, just promoting Trump’s app because they’re politically minded and all that.

Noooooope. They’re being paid.

Sophia says it’s just possible (journalist speak I assume) but I know exactly what I’m looking at and these guys, Conservative Hype House, are getting paid to drive traffic and app installs for Trump.

So how do you know that, Claire?

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The worst things I see among friends and people around me and in social media is they say who sees caste in 2020. They also say caste is wrong and it should be abolished. First friends please understand reality, don't come to a conclusion by seeing whatsapp forwards 1/n

Misleading YouTube videos and the common stuff that comes in cinema and in TV. First you must understand the biggest problem of India ia not Corruption but it's caste.Majority of movies we watch shows that that biggest problem of India is Corruption and if we stop it we will 2/n

Become a developed nation. But according to me these people are cheating us by hiding the biggest problem. For the people who say is there caste in 2020, I just want to ask a question. How many of you during your marriage search for your partner in same caste. 3/n

I think majority will do that, then how can you say there is no caste in 2020. Caste has just gone out of our names that too in TN only, but it's still there in everyone's home and everyone's minds. So please accept the truth and start your journey against it. 4/n

There is one group of people who speaks about everything about cinema, cricket and other stuffs, but when this topic comes to a discussion the becomes silent. I can understand that they don't want to speak about this because they may think it as a sensitive issue. 5/n
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Rajesh Raghavan
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Is WhatsApp already the Super App of India?

Thread 🧵


Below are a few insights I gathered while researching on how Gen-X use WhatsApp as a part of @10kdesigners Cohort!

Okay, let's go!

1/x

Gen-X? Who are they?

Gen-X (short for Generation X) are basically people with birth years around 1960–1980. That’s basically our (millennials’) parents!

2/x

Check out this detailed case study by @zainab_delawala

📮 Communication/Community

This is the primary feature of WhatsApp.

This feature is the entry point for most of the Gen-X, they come to WhatsApp to communicate and engage with small


- WhatsApp group is one of the most used features by Gen-X. Most of the message more on groups than on private chats.

- Forward messages received mostly are written in vernacular languages. They are all well scripted.

4/x
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mark pincus
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Tomorrow, Zynga shuts down FarmVille on Facebook after 11 years. I wanted to share the story of how we created it and why it has played such an important role in the evolution of gaming. 1/x

The real innovation of FarmVille was in making games accessible to busy adults, giving them a place to invest and express themselves and be seen by people in their lives as creative. People thought of FarmVille as a sort of Etch-a-Sketch. 2/x

It was the first game at scale that leveraged big data, and almost everything inside the game was tested and optimized. FarmVille became a training ground for a generation of entrepreneurs and product managers. 3/x

In 2008, Happy Farm reached 20+ million daily active users, setting off a wave of competition from game developers, and numerous farming games began to hit the market. 4/x.

On February 6, 2009, FarmTown reached 1 million DAU on Facebook. Farm Town combined the moving maps from MyFarm with avatars in Zynga’s YoVille. I wrote the date on the wall, and said we need to count the days until we are in the market with our own game. 5/x
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#keralatemples

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@SriramKannan77


Vigrahams and it suddenly started bleeding. Later Devaprashnam was held and thus found out that these were murthy's of Shiva and Vishnu which was worshipped long back. And thus temple is constructed here.
Om Namah Sivaye
Om Namo Narayanaya
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