If you are already in touch with Swift, you probably assumed that including third party libraries into your project would be useful. Railsware.com Mobile Developers and Alex Denisov, iOS Engineer and a huge Open Source fan, are ready to talk about it.
Making a custom framework that includes both ObjC and Swift code is very easy because Apple provides a mechanism to distribute code via frameworks (eventually, for iOS too). Next step into proper development is a creation of a pure Swift module, like Apple does with Swift’ std lib and Cocoa/Cocoa Touch bridge.
Basically, we are generating a simple module call Logger that will contain only one method: log.
You need at least three files to form a Swift module, so we should get all of them as an output:
Logger.swiftmodule – public interface/definitions
Logger.swiftdoc – docs (surprisingly)
libLogger.a – built library (there also might be a dylib, it depends on your task)
We can start with creating an unserviceable Logger library:
The class just takes some prefix and logs it before actual object:
Now it’s time to make a libLogger.a. The code will look like this:
xcrun swift -emit-library -emit-object Logger.swift -sdk $(xcrun --show-sdk-path --sdk macosx) -module-name Logger ar rcs libLogger.a Logger.o
-emit-library generates dynamically linked shared library, while -emit-object generates object file and includes main function, so you will have linker errors due to duplicated symbols.
The solution is simple: include both flags -emit-object and -emit-library, as is depicted above.
The next step is generating Logger.swiftdoc and Logger.swiftmodule:
xcrun swift -emit-module Logger.swift -sdk $(xcrun --show-sdk-path --sdk macosx) -module-name Logger
Now that you have a complete module, it is about time to integrate it into a real project. Create a simple Swift project and add the files:
Then setup “Import paths” for Swift:
You can now check out if your project works properly:
Voila!
Dealing with documentation is rather simple, as well. To add documentation to module you need to comment it using ///, e.g.:
You will see documentation on the right after its integration:
Note: to make it work after integrating, you have to restart Xcode.
This approach might not be applied for a regular iOS/OSX developer; it requires creating and supporting Make/CMake file, which complicates the process of generation. However, it may be useful if you want to create a pure module that does not include ObjC at all.
This is a guest post by Alex Denisov