Shared Mutable State

How can we deal with the complexities and troubles brought by shared mutable state in our code? Presented at AltConf 2018.

1. @gregheo AltConf, June 2018 Shared Mutable State !
2. @gregheo AltConf, June 2018 State
3. @gregheo AltConf, June 2018 Exclusive Shared Immutable Mutable
4. @gregheo AltConf, June 2018 Make it difficult
 to get wrong
5. @gregheo AltConf, June 2018 "
6. @gregheo AltConf, June 2018 queue1.async {
 
 } queue2.async {
 
 
 } 
 stuff()
 
 things()
 things2()

7. @gregheo AltConf, June 2018 Exclusive Shared Immutable Mutable private let private var
 private queue UIDevice
 Screen size &
8. @gregheo AltConf, June 2018 Fewer entry points
9. @gregheo AltConf, June 2018 internal
 private
 fileprivate
10. @gregheo AltConf, June 2018 Pass in values
11. @gregheo AltConf, June 2018 class Printer { var num: Int func print() { print(num) } }
12. @gregheo AltConf, June 2018 func printNum(num: Int) { print(num) }
13. @gregheo AltConf, June 2018 Who enqueues
 the queues?
14. @gregheo AltConf, June 2018 
 // call from anywhere!
 public func something() {
 privateQueue.sync { … } }

15. @gregheo AltConf, June 2018 Queue Callback
16. @gregheo AltConf, June 2018 
 // always call on the main queue!
 public func something() 

17. @gregheo AltConf, June 2018 
 // always call on the main queue!
 public func something() {
 dispatchPrecondition(condition: .onQueue(.main))
 }

18. @gregheo AltConf, June 2018 # Do I have order right? Is the order even knowable? Is it concurrent?
19. @gregheo AltConf, June 2018 $ Too much access Mutable variables Thread uncertainty
20. @gregheo AltConf, June 2018 ✅ “Limit access “Functional” approach “Private queues
21. @gregheo AltConf, June 2018 # $ ✅
22. @gregheo AltConf, June 2018 Make it difficult
 to get wrong