Wrapping Objective-C Frameworks in Swift

Wherein we discuss the trials and tribulations endured while wrapping Realm's Objective-C interface in a Swift framework. You'll learn how to craft the perfect Swift interface without duplicating core functionality, as well as tricks to work around tooling limitations. Why let Objective-C die in sadness when we can just hide it in a shiny new Swift suit?

Transcript

1. Lessons Learned Wrapping an Objective-C Framework in Swift NSLondon JP Simard, @simjp, realm.io 1
2. Why? 2
3. Why? API Improvements // Go from this: func objcFunc(a: AnyObject!, b: NSArray!) -> NSString! // to this: func swiftFunc(a: ClassA?, b: [Int]) -> String? // Or using autoclosures, generics, // default parameter values, making types // and optionality explicit, etc. 3
4. Why? To Expose Unmappable Interfaces // Objective-C variable arguments aren't exposed to Swift + (RLMResults *)objectsWhere:(NSString *)format, ...; // neither are #defines #define NSStringFromBool(b) (b ? @"YES" : @"NO") // or certain declarations NSVariableStatusItemLength 4
5. Why Not Rewrite in Swift? 1. Lazy 2. No significant gains from the language 3. Existing codebase complex and/or mature 4. Yup, still lazy 5
6. Step 1: Make dynamic objc framework 6
7. Porting an API RLMObject // ObjC Realm.Object // Swift RLMObject.allObjects() // ObjC objects<T: RLMObject>(type: T.Type) // Swift 7
8. Packaging 1. Dynamic framework, logical 2. Can't statically link Objective-C framework in Swift framework (no modules) 8
9. Exposing Just the Right Interfaces 9
10. Exposing Just the Right Interfaces Making sure Objective-C is still import-able 1. Module Map needs to be preserved 2. Must be a dynamic framework 10
11. Step 2: Setup Swift framework target 11
12. Make Sure Your Framework Compiles ... —when building standalone —when building a target which links against it 12
13. Exposing Just the Right Interfaces Exposing private interfaces just for Swift binding Unfortunately there is no private bridging headers for framework targets 13
14. Exposing Just the Right Interfaces Exposing private interfaces just for Swift binding framework module Realm { umbrella header "Realm.h" export * module * { export * } explicit module Private { header "RLMRealm_Private.h" } } 14
15. Exposing Just the Right Interfaces Don't subclass import Realm class Realm: RLMRealm { // What's wrong with this? } 15
16. Exposing Just the Right Interfaces Don't subclass. Wrap! import Realm class Realm { private var rlmRealm: RLMRealm private init(rlmRealm: RLMRealm) { self.rlmRealm = rlmRealm } } 16
17. Testing 1. Don't test functionality, test interfaces 2. Write equivalency tests 17
18. Documentation 1. Compare Objective-C & Swift interfaces side by side 2. Copy docs from Objective-C 3. Convert doxygen format to ReST 18
19. Publishing —Carthage —CocoaPods 19
20. Links —This talk: github.com/jpsim/talks —Realm: github.com/realm/realm-cocoa —RealmSwift: realm/realm-cocoa/tree/al-swift —jazzy: github.com/realm/jazzy 20
21. Thank You! 21
22. NSLondon().questions?.askThem! JP Simard, @simjp, realm.io 22