Evolution of Asynchronous Programming on iOS

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Ash Furrow, Artsy (on iOS) Evolution of Asynchronous Programming

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Evolution of Async Programming

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Agenda • All decisions are made in a context • iOS developers are human; we tend to conﬂate things • Older solutions have value, too • There are beneﬁts to using older technology

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(•_•) <) )╯ / \ \(•_•) ( (> / \ (•_•) <) )> / \ Decisions are made in a context

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What’s a context?

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Contextual Questions • What technology is available? • How much do I understand the options? What about my team? • How popular is the technology? • How stable are the tools I would need to use? • How easy is it to learn? • How quickly do I need to complete the task?

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Decisions aren’t made in a vacuum

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Unique, in space… and time

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Adopting a codebase

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Context includes experience

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But you don’t have to You can never understand the context a decision was made in

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It is enough to appreciate that a context existed

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Be empathetic

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iOS developers conﬂate things ⽌ •́ ﹏ •̀ ⽎

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conﬂate verb [ with obj. ] combine (two or more ideas, texts, etc.) into one.

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Humans look for patterns

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What does this have to do with iOS development?

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Some popular development practice When learning iOS, we’re bad at that practice Popular development practice is bad + =

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We get better at iOS development New thing comes out, and we’re good at it New thing is good + =

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This is why new things are always so appealing

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Why do iOS devs do this? There are several explanations

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iOS is young … really young

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Always older APIs for us to blame iOS is constantly changing

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I’ve done this a lot You probably have, too

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Only human

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Remember… Don’t be hard on yourself!

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And don’t be hard on others! We’re all just winging it!

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⊂_ヽ　＼＼ Λ＿Λ 　　＼(　ˇωˇ) 　　 /　⌒ 　　/ へ＼　 / 　/　＼＼ ƀɹϊɹɹ ヽ_つ　 /　/ 　(　(ヽ　|　|、 \ 　| ⼃丿＼　| |　　) / ノ )　　Lů Older solutions have merit

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–Lots of people, for hundreds of years “Those who don’t study history are doomed to repeat it.”

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Wrong

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–Me, just now “Those who don’t study the past can’t make informed decisions about the present.”

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History of Async Programming

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performSelector: Family • iOS 2+ • Easy(ish) • Supports delays • Cancellable(ish) • Threadsafe(ish)

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NSThread • iOS 2+ • Difﬁcult, mostly • Sometimes, kind of cancellable • Complicated

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NSOperation • iOS 2+ • Supports concurrency • Supports dependency graphs • Cancellable • More boilerplate

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Blocks / GCD • iOS 4+ • Super-easy • Super-dangerous (reference cycles) • Better in Swift • Not cancellable

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NSOperation + Blocks • iOS 4+ • Everything from NSOperation, but also with blocks • Less boilerplate • Slightly more verbose than blocks (this is Objective-C, remember) • Not popular – why?

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NSProgress • iOS 7+ • Confusing • No one knows what it’s for • I don’t know • Do you know?

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NSURLSessionTask • iOS 7+ • Network-speciﬁc async abstraction • Very nice • Seriously, very nice • (Will discuss more later)

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Let’s build something Those are only tools

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Abstraction Blocks Function pointers NSOperation ???

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Example Abstractions • Adding block callbacks to UIGestureRecognizer, UIAlertView, etc • Futures, promises • Sequences, signals (FRP)

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Those are great abstractions, but… I feel we ignore NSOperation

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NSOperation • Cancellable • Chainable, dependency graphs • Concurrency support • Completion handlers • Prioritization • Interoperate with GCD

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Why so GCDerious?

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Why GCD? • iOS devs favour GCD over other suitable abstractions • Why? • NSOperation is unfamiliar, feels unnecessary • Not-invented-here-syndrome • Apple is good at marketing

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Different solutions work for different problems

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Get familiar with your options

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Don’t be mean to developers who disagree with you

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There are beneﬁts to older solutions (╯°□°）╯︵ ┻━┻

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Developers (like me ) tend to say Objective-C is “old and busted”

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Old, yes, but not busted

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Older Technology • “Old” is stable • “Old” is usually well-documented • “Old” is easy to hire for • “Old” has a lot of helpful resources, libraries, tutorials, etc

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AFNetworking uses NSOperation

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Let’s look at another example

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NSURLSession • Very protocol-oriented • NSURLSessionDelegate • NSURLSessionTaskDelegate • NSURLSessionDataDelegate • NSURLSessionDownloadDelegate

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NSURLSession • Separate delegates isolate different areas of concern • One object may conform to all protocols • Many, small protocols are better than one massive one • Swift protocols don’t even support optional functions!

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NSURLSession • Could have been completely blocks-based… • Instead, based on ideas behind NSOperation • NSURLSession probably wraps an NSOperation, anyway • This is good! No leaky abstractions

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Try to be more like NSURLSession

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Go read NSOperation.h

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Wrap Up • Decisions are made in an unknowable context • Developers are bad at evaluating things • New and shiny things aren’t always better • Old solutions carry extrinsic beneﬁts