iOS Module Intro

1. iOS Module Intro JJ Lin
2. Topics covered • #include #import • .pch • Clang Module ◦ pcm ◦ .modulemap • Swift Module ◦ .swiftmodule ◦ .swiftinterface • Umbrella header • Umbrella framework
3. Preprocessor
4. History before Module…
5. #include at ObjC
6. #include at ObjC • Naming collistion • Prevention ◦ AFURLSessionManager ◦ NSObject
7. #include at ObjC • Duplication, compile error • Need #include guard
8. #import at ObjC • No need #include guard • Clang determines if this header has been included already ◦ avoids duplicate inclusion
9. #import at ObjC • Compile-time scalability ◦ N translation units ◦ M headers ◦ In each translation unit, the compiler is performing M x N work ◦ Even though most of the M headers are shared among multiple translation units • Translation unit ◦ consists of a source file after it has been processed by the C preprocessor, meaning that header files listed in #include directives are literally included
10. Pre Compiled Header • .pch • Precompile that bundle of headers into a single precompiled header (PCH file). • Then, when compiling the source files in the project, we load the PCH file first. • Drawback ◦ Every .m can access the .pch
11. Clang Module • Binary .pcm • Usage ◦ @import ◦ And also #include and #import after turn module ON
12. Clang Module • Problems Clang Module do NOT solve: ◦ Naming collistion in the only one namespace
13. Clang Module - modulemap Defines • Umbrella Header: UIKit.h • Sub module which needs to export: All • Linked framework: UIKit
14. Umbrella Header • Umbrella: something that includes or represents a group or range of similar things. 綜合體 (from Cambridge Dictionary) • Master header for a framework
15. Umbrella Framework (by the way…) • Duplicate • Difficult for dependency and version control • Might only suitable if all the frameworks are custom frameworks
16. Swift Module • The closest analogy to C-style header files in Swift is the .swiftmodule file • Binary format (LLVM bitcode) file that records the declarations (types, function signatures, etc.) • When you import that module from another module that you're compiling, `swiftc` loads that `.swiftmodule` file into memory so that it can typecheck in that module. • Has namespace in module
17. Swift Module • Internal compiler data structures ◦ Contains Abstract Syntax Tree(AST) ◦ Swift Intermediate Language(SIL) of framework’s public API.
18. .swiftinterface • Swift Module Stability
19. .swiftinterface • Includes the version of the compiler that produced this interface • Also contains the subset of command line flags that the Swift Compiler needs to import this as a module.
20. .swiftinterface • List all the modules that this framework imports • Dependency graph !
21. .swiftinterface • Include the public API, but not private • class has a de-initializer in the interface. If don't provide an explicit de-initializer, the compiler generates one
22. .swiftinterface if you make an enum without any associated values, then the compiler implicitly makes that conform to an Equitable and Hashable
23. ObjC Interface of Swift Framework • Xcode's default template ◦ Objective-C Umbrella Header ◦ Generated header ▪ containing the Objective-C parts in the framework
24. ObjC Interface of Swift Framework • Objective-C Umbrella Header
25. ObjC Interface of Swift Framework • Generated header: Framework-Swift.h ◦ containing the Objective-C parts in the framework
26. ObjC Interface of Swift Framework
27. Reference • https://clang.llvm.org/docs/Modules.html#problems-with-the-current-model • https://tech.meituan.com/2021/02/25/swift-objective-c.html • Binary Frameworks in Swift