Pragmatic Swift

Pragmatic Swift
Blake Merryman

A collection of "use everyday" tips & tricks 
to help keep your code base  
maintainable, understandable, & extendable.

Covered tonight…
Documentation
Organization
Striving for Smallness
Access Control
Early Exits
Collection-Type APIs
Property Initialization
Lazy Loading
Lazy Sequences
Slow Build Times

Documentation
Save valuable time when ⌥ + clicking around
Easily write rich Quick Help docs in Markdown
Add quick notes to function, variable, etc.:
/// Important (but brief) QH note.
Auto-document functions: ⌘ + ⌥ + /

Documentation
Useful comments… 
// TODO: *** Shows in Jump Bar ***
// NOTE: Something important!
Integrate these into build systems with scripts  
or special tools (e.g. swiftlint)

Documentation
// Forces Xcode to flag a warning at compile time
// Source: http://stackoverflow.com/a/26869489/1418335
// Disclaimer: Not tested; I use swiftlint :)
if [ "${CONFIGURATION}" = "Debug" ]; then
TAGS=“TODO:|FIXME:"
echo "searching ${SRCROOT} for ${TAGS}"
find "${SRCROOT}" ( -name "*.swift" ) -print0 | xargs -0 egrep
--with-filename
--line-number
--only-matching "($TAGS).*$"
| perl -p -e "s/($TAGS)/ warning: $1/"
fi

Organization
A well organized project can save hours of time
Files are Free!
Group according to large ideas
Extensions are great for grouping functionality: 
// MARK: - Private Helpers
extension MyViewController { /***/ }
// MARK: - + UICollectionViewDataSource
extension MyViewController: UICollectionViewDataSource { /***/ }

Strive for Smallness
Being small at scope improves understanding
Take advantage of typed parameters: 
func configure(_ cell: MyCollectionViewCell, at indexPath: IndexPath)
func configure(_ cell: YourCollectionViewCell, at indexPath: IndexPath)
func configure(_ cell: TheirCollectionViewCell, at indexPath: IndexPath)

Strive for Smallness
How else can we keep things small? 
 
Extensions, Data Sources, Network Stacks,  
Inheritance, Composition, Rich Enums,  
Generics, Access Control

Access Control
What is need to know and Who needs to know it?
Access Control dictates how an API is viewed
Levels:  
private, ﬁleprivate, internal, public, open
Tips: 
- Use private to hide extension helpers 
- Use ﬁleprivate to hide extensions

Early Exits
Help prevent nesting
Important validation logic is up front
Clearly indicates success/failure
Prefer “guard” over “if”

Early Exits
// Not Preferred
if let a = optionalA, a.someBoolean == true {
// Do GOOD thing :)
}
else {
// Do BAD thing :(
}
// Preferred
guard let a = optionalA, a.someBoolean == true else {
// Do Bad thing :(
return
}
// Do GOOD thing! :D
❌
✅

Take advantage of new closure-based APIs to 
keep logic tight & readable
Chainable to allow for building complex logic fast
Great reference implementation for using 
Protocols (with default implementations) + Generics

var numbers = [Int]()
numbers += 1...1_000
var oddNumbers = [Int]()
for x in numbers {
if x % 2 != 0 {
oddNumbers.append(x)
}
}
var multNumbers = [Int]()
for x in oddNumbers {
let x10 = x * 10
multNumbers.append(x10)
}
for x in multNumbers {
print(x)
}
// Prints: 10, 30, 50, ..., 9950, 9970, 9990

numbers += 1...1_000
numbers.filter { $0 % 2 != 0 } // Grab all of the odd numbers
.map { $0 * 10 } // Multiply by 10
.forEach { print($0) } // Print out new values
// Prints: 10, 30, 50, ..., 9950, 9970, 9990

class MyViewController: UIViewController {
var collectionView: UICollectionView?
override func viewDidLoad() {
super.viewDidLoad()
let flowLayout = UICollectionViewFlowLayout()
flowLayout.scrollDirection = .horizontal
collectionView = UICollectionView(frame: .zero,  
collectionViewLayout: flowLayout)
collectionView?.translatesAutoresizingMaskIntoConstraints = false
collectionView?.isPagingEnabled = true
collectionView?.backgroundColor = .clear
collectionView?.showsHorizontalScrollIndicator = false
view.addSubview(collectionView!)
// Auto Layout Code ...
}
}

let collectionView: UICollectionView = {
let flowLayout = UICollectionViewFlowLayout()
flowLayout.scrollDirection = .horizontal
let collectionView = UICollectionView(frame: .zero,  
collectionViewLayout: flowLayout)
collectionView.translatesAutoresizingMaskIntoConstraints = false
collectionView.isPagingEnabled = true
collectionView.backgroundColor = .clear
collectionView.showsHorizontalScrollIndicator = false
return collectionView
}()
// MARK: - Lifecycle
super.viewDidLoad()
view.addSubview(collectionView)
}
}

Lazy Loading
Initialize at access rather than init 
lazy var collectionView = UICollectionView.configuredCollectionView()
super.viewDidLoad()
}
}

Lazy Loading
ProTip: Limit the scope of setter with Access Control 
private(set) lazy var collectionView = UICollectionView.configuredCollectionView()
super.viewDidLoad()
}
}

Lazy Loading
Constants declared at global scope & statically are
lazy by default. Does not apply to constants
declared at instance scope.

Lazy Sequences
lazy property on SequenceType & CollectionType
Lazily access elements in sequences/collections
Huge performance beneﬁt!
Easy to implement…

Lazy Sequences
numbers += 1...1_000
let newNumbers = numbers
.filter { $0 % 2 != 0 } // Executed 1,000 times
.map { $0 * 10 } // Executed 500 times
newNumbers.last
All calculations completed before access!

Lazy Sequences
numbers += 1...1_000
let newNumbers = numbers.lazy
.filter { $0 % 2 != 0 } // Executed 1 time
.map { $0 * 10 } // Executed 1 time
newNumbers.last
Calculations performed as needed on access!

Slow Build Times
Sometimes Swift build times are slow 
(**cough** type inference **cough**)
Setting to add build times to logs: 
- Project Settings > Build Settings > Other Swift Flags 
- Add -Xfrontend -debug-time-function-bodies 
- “Expand All Transcripts” (look for new XX ms)

Slow Build Times
Pro Tip: Prioritize build time optimizations:
“Copy transcripts for shown results” for logs then in
Terminal, run:
pbpaste | egrep '.[0-9]ms' | sort -t "." -k 1 -n | tail -10
Highlights the top 10 build time hogs in project

Sources
https://developer.apple.com/reference/swift
http://stackoverﬂow.com/a/26869489/1418335
https://thatthinginswift.com/kill-your-viewdidload/
http://alisoftware.github.io/swift/2016/02/28/being-lazy/
https://thatthinginswift.com/debug-long-compile-times-swift/
https://twitter.com/erikaderstedt/status/725217977314992128

Pragmatic Swift

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