Blog Post: https://www.meta.sc/tech/swiftobjc If you are hitting roadblocks in trying to communicate with Core Foundation and C APIs directly from Swift, just wrap them in a friendly Objective-C class that provides an simple API for the rest of your application to use.

1. Facilitating Idiomatic Swift
with Objective-C
Aaron Taylor
aaron@meta.sc
June 15, 2015

2. • Started in pure Swift
• Concision
• Type safety, esp. in data structures
• Functional aspects

3. • Unmanaged data types for unannotated APIs
• All of the ones we are working with
• Documentation issues
• Fix the compiler errors, then get runtime errors
• Lots of head scratching
Core Foundation in Swift

4. getting a file’s MIMEType using UTType
vs.

5. • UnsafePointer, UnsafeMutablePointer,
AutoreleasingUnsafeMutablePointer
• wrap Swift types, clutter your code
• CFunctionPointer
• unavailable in Swift*
Interacting with C APIs

6. Creating an FSEventStream

7. Benefits of Swift are lost
• No longer writing idiomatic Swift
• Type safety (mostly) gone
• Objective-C is more concise
• Basically writing C with more verbose syntax

8. Reclaim the
benefits of Swift
• Wrap Core Foundation and C interactions with
Objective-C classes providing specific functionality
• For us: FileSystemListener and FileSystemCrawler
• Provide a clean API for your project’s use

9. Objective-C and Swift
• Bridging by the compiler
• Syntactic Translation
• Data types
• Cocoapods
https://developer.apple.com/library/ios/documentation/Swift/Conceptual/
BuildingCocoaApps/index.html

10. Bridging
• Header file used to generate Swift bindings
• @objc creates Objective-C bindings for Swift code
• as does inheriting from an Objective-C class

11. Syntactic Translation
• Intuitive conversions for initializers and methods
• unannotated initializers automatically unwrapped
• At the Cocoa level, most things just work

12. Data Types
• Type safety of Swift lost in default cocoa datatypes*
• Conversions are easy
• Some automatic, others just a cast

13. Cocoapods
• Pods written in Swift are treated as dynamically
linked frameworks
• Requires use_frameworks! in your Podfile
• blog.cocoapods.org/CocoaPods-0.36/
• blog.cocoapods.org/Pod-Authors-Guide-to-CocoaPods-Frameworks/

14. Remaining Issues
• Some type safety lost in interop with swift code
• New Objective-C generics help!
• Compiler optimization turned off
• significant performance hit, orders of magnitude
difference in some cases
• Look into `@_semantics(“optimize.sil.never”)`

15. Xcode 7
• Support for CFunctionPointer from closures and
swift functions
• Native support for C function pointers: C functions that take function
pointer arguments can be called using closures or global functions, with
the restriction that the closure must not capture any of its local context.
(16339559)
• Generics in Objective-C
• Typed data structures translate to swift

16. References
• https://developer.apple.com/library/ios/documentation/Swift/Conceptual/
BuildingCocoaApps/WorkingWithCocoaDataTypes.html
• https://developer.apple.com/library/ios/documentation/Swift/Conceptual/
BuildingCocoaApps/InteractingWithCAPIs.html
• https://developer.apple.com/library/ios/documentation/Swift/Conceptual/
BuildingCocoaApps/MixandMatch.html
• https://developer.apple.com/swift/blog/?id=6
• http://dev.eltima.com/post/93497713759/interacting-with-c-pointers-in-swift-
part-2
• http://www.charlessoft.com/hacks/using_c_function_pointers_in_swift.html

17. access any file in seconds,
wherever it is.
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