playgrounds-2017.md

Playgrounds Conference 2017

The following are my on the fly notes taken at the 2017 Playgrounds Conference in Melbourne.

Disclaimer: There may be some errors

Day One

Swift On The Server

Chris Bailey, IBM

• BFF - back end for front end
• a layer that allows the frontend device to access backend hosted services
• web cares alot about first paint time compared to mobile which already has the UI in place
• https://swapi.co/api/people/1/
• to get a piece of information, may need 3 requests
• GraphQL allows you to request particular sub objects, but means more work in the client
• BFF - allows a custom layer infront of the API that has tailored request/responses
• Suggests that the frontend team writes their own BFF layer
• This means less assumptions and more understanding
• They can write the BFF layer in their native language (js/java/Swift)
• Aim is not to duplicate code, but to have the platform specific APIs only in the BFF
• https://github.com/IBM-Swift/Kitura.git
• $ swiftservergenerator
• kitura.io

High Performance Swift

Matt Gallagher, Cocoa with Love

• How fast is Swift compared to ... c?
• Why is C considered the baseline for performance? Abstractions (or the lack therof)
• C is close to a 1:1 mapping to assembly
• MT19937_64 Mersenne Twister Random Number Generator
• Result: C 0.62s vs Swift 1.04s (of a naive implementation)
• Performance profiling analysis
• Speed up usage of arrays with withUnsafeMutableBufferPointer for looping
• var &+ 1 for an unchecked addition (we don't care about overflow)
• Final result Swift run in 0.52s - with alot of cheating
• But the performance is actually identical if these steps are taken

Your Refactoring Toolbox

Rachel Bobbins, Stitch Fix

• Refactoring is a lot like renovating
• Tools: Deprecation warnings, Other compiler warnings
• Know the problem. Have a vision
• Temporarily deprecate a method to see the scope of the required change
• Temporary protcols - to help bridge the old and the new
• Tests - use them to make sure critical paths don't break

Everything You Ever Wanted To Know About Sequence and Collection

Soroush Khanlou, Fatal Error Podcast

• Sequence > Collection > BidirectionalCollection > RandomAccessCollection > RangeReplaceableCollection
• Sequence: a list of elements, can be infinite, iteration not always repeatable
• Iteator.Element
• Implement a linked list as an enum because its swifty
• indirect please let me reference myself within myself and don't freak out
• Conform to Sequence and you get all the good stuff for free: forEach, map, filter etc
• Next, lets extend Sequence with a count function
• Easy, something a bit harder is to extend it with the eachPair function
• Collection inherits from Sequence, always finite and iteration is repeatable

Cooperative Path Finding

Matt Comi, Big Bucket Games

• Heuristic - the approximate cost of moving from a tile to a destination
• Manhattan distance hueristic - tells you how many moves to the destination
• A* Algorithm - uses the Heuristic, the exploration is guided by the hueristic
• Start at the origin, calculate the cost of getting to the destination
• Loop outwards adding tiles to the closed set when they have the lowest cost
• When the destination is found, reverse the array and you have a path

Once Upon a Rewrite

Wendy Lu, Pinterest

• Pinterest rewrite from 2015-2016, took about a year
• Optimise data sent over the API
• App startup time
• Concurrency
• AsyncDisplayKit to configure views and lay them out off the main thread
• Immutable model layer
• Shared state can be an issue if multiple writers can modify the same model
• Autogenerated model classes - JSON Scheme > Model class files
• Builder object pattern: a mutable representation of an immutable object
• PINCache
• Merge the new data with the cached version and update the cache on object init
• http://moreindirection.blogspot.com/2014/08/nsnotificationcenter-swift-and-blocks.html
• https://engineering.pinterest.com/blog
• https://github.com/linkedin/RocketData

How to Clang Your Dragon 🐉: Building Compilers with LLVM

Harlan Haskins, Bryx & Student

• A compiler is a translator
• Input > Lexer ~> Token Stream > Parser ~> AST > Code Generator
• AST = Abstract Syntax Tree
• LLVM is a set of libraries for Compilers
• Centered around LLVM intermidate representation

Code Signing Demystified: Certificates, Private Keys And Profiles

Marin Usalj, Lyft

• Quote from apple
• As a user, you're sure you're getting authorized software
• Protects developers from unauthorized copying
• No competition for the App Store (iOS)
• Things break
• Important to understand the underlying technology
• Relies on public-key cryptography based on X.509 standard
• Introduced on OS X 10.8 - Gatekeeper
• CSR consists of info, algorithm and the signature (a public/private key pair is created)
• $ openssl asn1parse
• RSA 2048 bit
• Public key used for the request
• Private key used to sign the binary
• Certificate - a public key combined with some additional information
• The additional info is signer data (issued by Apple, valid til, etc)
• Once again, can use openssl to read the contents of the CER file
• PKCS#12 - archive file format for saving multiple crypto objects in a single file (.p12)
• Team, Bundle, App ID
• App ID is a team id + a bundle id (eg 4R5GH57P.com.yolo.ios.beta)
• Entitlements - iCloud, get-task-allow (only allow in debug), plist
• $ codesign -d --entitlements :- Yolo.app
• Provisioning profiles - contains the app id, cert, entitlements, an ID and an expiry date
• $ security cms -D 0i Yolo.app/embedded.mobileprovision
• tip: use .xcconfigs if you can for code signing settings

Putting Together The Best CI Workflow For Swift Apps

Dennis Pilarinos, buddybuild

• Review software development lifecycle
• Web app continuous build systems are better established than native apps
• Limitations of TestFlight (multiple versions, staging, confusing for users)
• Lots of slides of project usage stats data

Understanding Why Strings Are Evil

Samuel Giddins, CocoaPods

• Strings
• Unformatted data, often have meaning beyond the bytes
• The universal data type? Think UDID, JSON
• C strings are just arrays of chars
• In Objective-C they are backed by a class cluster NSString
• In Swift, String is a value-type struct, which is pretty complex
• Encoding. ASCII, Unicode, et al
• Unicode - puts all characters in a single encoding. Every character. Every language. Unique code/number for each one.
• Swift strings are Unicode-aware (can correctly compare two versions of the same strings)
• 📐 performance, correctness, shipping - choose 2

Playgrounds

Jason Brennan, Meetup

• What is education about? What can we as programmers to do to help?
• Alan Kay - an inspiration
• Book: Mark Johnson - The Meaning of the Body
• Book: Daniel Kahneman - Thinking, Fast and Slow
• Reality is a hallucination 🤔
• We must ensure that human wisdom exceeds human power - Vi Hart
• What to do about it?
• Learn! (read books)
• Learning is hard, you have to train yourself over years to do it!

Day Two

Comparative Asynchronous Programming

Ash Furrow, Artsy

• Synchronous programming is 'normal' programming
• CPU time is valuable and we don't want to waste it
• Asynchronous programming is executing code out of order from the way its written
• You can resume async code later on due to an external event
• Abstractions and tradeoffs, some languages are quite opiniated
• Node JS only has 1 thread, so alot of it is non-blocking
• Imagine if every function returned via a completion handler!
• Swift has built in async capabilities
• GCD - Grand Central Dispatch
• NSOperationQueue is built on top of GCD
• Check out DRBOperationTree, open sourced by Artsy
• Target/Action - used mainly by UI controls
• Callbacks / Completion handlers - short anonymous functions that execute at a later point in time
• Can lead to Callback hell - the traingle of doom
• enum Result<T> { case success(T); case error(Error) } (result types are monads)
• Ok to use callbacks, they are good, but sometimes you need a better abstraction
• Promises/Futures
• Great to reduce the nesting, single point to handle errors
• Functional Reactive programming
• Streams of observables
• FRP is at its best when you are sent a stream of values over time
• FRP has a learning curve, but is a great option
• Actor Model
• Adds constraints and conditions on how you write your code that makes it complicated but very robust
• All the comms between actors is handled by message passing
• What about things we can't do in Swift?
• Async / Await - allows you to write async code that looks sync
• Coroutines and Generator Functions 🤔

Five Unbelievable Secrets Of Reactive Programming The Experts Don’t Want You To Know!

Greg Heo, Instagram

• 🤐🔐
• 1. You already know it!
• Data flows, propagation of change, how data travels as inputs into your program and then as output
• 2. Sequences everywhere
• Everything is a sequence
• An iterator is a sequence
• Sequences aren't indexable, have a single direction and are unbounded?
• 3. Small pieces of logic
• 4. Declarative style
• Think of UIStackView as declarative opposed to layoutSubviews() which is imperative
• 5. Testable code
• Can mock data with a sequence of test data, eg an array

Swift at Scale; Rewriting the Uber app

Alan Zeino, Uber

• Uber scaled from a team of 10's to 200 iOS engineers
• We had a 5,000 line view controller
• Presidio - cool internal code name for the project of Rewriting
• Built in monitoring and analytics, with an opt-out policy
• De-risk experimentation - application framework with Plugin API
• "Riblets" design pattern - RIB - Router Interaction Builder
• And optionally, a Presenter and a View
• http://t.uber.com/rider-app
• 8000 .swift files, about 10% are code generated
• 700,000 lines of Swift
• Compile times increased alot due to Swift
• swiftc -Onone -whole-module-optimization
• -Xfrontend -warn-long-function-bodies=100
• Optimise the number of dylibs as this affects the startup time of the app as the OS loads the
• Takes 250ms to load the Swift standard lib on iPhone 6s
• Swift 3 migration - 160867 insertions, 105132 deletions - ouch
• Keep an eye on compile times
• No compiler setting is untouchable!
• Too many dynamic libs can hurt your startup performance
• Consider using Buck
• File radars because Apple needs them

Opinionated Code

Erica Sadun, Author

• Style rules are personal choices
• Why style?
• Code should be invisible
• Focus on meaning
• Reduce cognitive load
• Uniformity
• Consistent rules produce consistent code
• Underscores in numbers? 1732500 vs 1_732_500
• Same for hex strings 0xffffff vs 0xff_ff_ff

Scaling Open-Source Communities

Felix Krause, fastlane

• 4 stages of open source projects
• 1. Publish source code
• 2. Developers start using your project
• 3. Go-to solution in its field
• 4. Hyper scale projects
• Keeping the momentum
• Handling support
• Reviewing PR's can take as long as just writing the feature itself
• Maintainers are so busy maintaining, they stop using the product, which is a problem
• How to scale open source projects
• Improve your error messages
• Make it easy to find existing issues
• Use bots to filter issues and PRs to filter out the noise
• Responding to pull requests danger
• Be welcoming and friendly 😃
• Local extensions / plugins ro allow developers to extend/customise the functionality for their project

SpriteKit No Magic Required

Hecthor Matos, Capital One

• The Game Loop
• Lag is introduced when your update code takes longer than its alloted in the run loop, causing the next frame to be dropped
• Contact detection/collisions
• SKPhysicsContactDelegate
• For collision behaviour at least one physics body must have a collision bitmask
• Bitmasks are the most efficient way of comparing sprites
• Architecture
• Single responsibility principle
• https://github.com/KrakenDev/SuperMarioWorld

Unit Testing For Designers

Tamar Nachmany, Tumblr

• Do the designers I work with know this concept?
• Have I taken the time to explain to designers how the code/UI layout works?
• Anyone can become a teacher
• Software developlment is the reuse of logics and types across a system
• Unit tests validate individual units of code by executing logic and asserting expected results
• Unit testing is a vehicle for change
• Unit testing automates identifying new issues
• Tests reflect the construction of a codebase or a type
• Modularity is how units become units
• Safety is the reduction of chaos
• Designing a test is a type of abstraction
• Innovation - Don't learn by example, be the example

How I Learned To Stop Worrying And Love Mutation

Chris Eidhof, objc.io

• Functional programming dogma - immutability is the best
• Mutability can make code harder to read as you need to keep track of the current value
• Immutable objects are good for multi threading or async code
• Structs will solve everything - if you let struct then its values are constant (as opposed to an object)
• The mutablily of a struct is controlled by let vs var
• mutating keyword on a struct's func tells you that self is mutable
• Ctrl+Opt+Cmd+F - fix all in scope - handy keyboard shortcut
• A new var for a struct is a new copy, as opposed to a new reference for an object
• Array's are structs so can be treated the same

Taming Touches And Taps

Adam Bell, Facebook

• What made iOS so good? Interaction and Animation
• How can we remove some of the waiting from animations? (So we can interact with the screen all the time)
• Interruptible animations - should be interrupted, cancelled or ignored, begin again with or without interaction
• UIScrollView is interruptable
• Without interruptibility, apps feel laggy, unresponsive or broken
• iOS has been making improvements to this, in the OS and in the animation APIs
• Pro-tip: UIView animations are kind of limiting when it comes to prematurely cancelling animations
• POP is an animation open source animation framework
• Selective interruptibility - should avoid blocking user interaction when possible
• It requires a bit more work, but is worth it to improve usability

Side note: (All/most?) speakers from the northen hemisphere had 1 slide in their deck upside down 🙃🇦🇺