As of Xcode 12, Apple has matured Swift Bundle Manger to a level the place it is smart so as to add assist for Swift packages to your libraries. There are nonetheless just a few stumbling stones on the trail which haven’t any apparent answer. So I determine, I’d share with you ways I obtained round them after I just lately added SPM assist to DTCoreText, DTFoundation and Kvitto.
Earlier than SwiftPM, my basic strategy for a library can be to have all library code in a `Core` subfolder, with a `Supply` folder containing code which will get compiled and a Assets folder for all types of sources, like for instance asset catalogs or XIB recordsdata.
A Little bit of Historical past
For the primary 7 iOS variations the product of this product might solely be a static library, Apple solely launched the flexibility to create dynamic frameworks for Goal-C as of iOS 8. With Swift it was the opposite approach round: you can solely have dynamic frameworks with Swift code. For the primary 4 variations of Swift the ABI (Utility Binary Interface) was an excessive amount of in flux to permit a statically linked product. With Swift 5, in 2019, we lastly obtained the required stability and thus Xcode gained the flexibility to provide static libraries containing Swift code. That is additionally the principle cause why Xcode all the time added a bunch of dylibs to your apps, containing Swift wrappers to all of the frameworks your app could be interfacing. These dynamic libraries are the third form of libraries now we have encountered up to now.
Oh boy, I bear in mind all of the hackery we needed to do to provide a „pretend“ framework that was primarily a fats static library (with slices for all supported processors) and all public headers. We’d that in order that any person utilizing our library might drop it simply into their venture and have all uncovered interfaces be seen. In Goal-C you would wish to have the header recordsdata obtainable for public capabilities and courses contained within the library. These `.framework` bundles supplied a pleasant encapsulation of that, in order that it was nearly like dealing with a single package deal including a third-party framework to your app.
Dynamic frameworks – in actual life, on gadget – truly don’t include any headers any extra as these change into ineffective after compiling. The principle good thing about first-party dynamic frameworks is that Apple can have their APIs and code shared between all apps put in on the gadget. The one and solely UIKit framework – put in as a part of iOS – is being accessed by and dynamically linked to all put in iOS apps. Solely a single occasion is current in RAM at any time. Customized frameworks can’t be shared between a number of apps on account of all apps being contained in their very own little sandbox. Each iOS app containing DTCoreText for instance has to have its distinctive copy of it inside its app bundle. If an app has a substantial amount of third-party frameworks that technique of loading all frameworks into reminiscence and dynamically linking can noticeably decelerate app launch.
Swift By no means Had Headers
With the improvements introduced with Swift additionally added the idea of modules to Xcode. The Swift Programming Language Web site gives this definition of modules.
A module is a single unit of code distribution—a framework or software that’s constructed and shipped as a single unit and that may be imported by one other module with Swift’s import key phrase. Every construct goal (corresponding to an app bundle or framework) in Xcode is handled as a separate module in Swift.
Whenever you import a module in your code, then Xcode by some means magically is aware of all concerning the public interfaces contained in it, with out ever having to have a separate header file. I don’t understand how precisely that works, however I’m glad that it does!
It was the issue of discovering and integrating third-party libraries into your codebase, that Cocoapods was invented to resolve. The primary public launch of it was nearly precisely 9 years in the past, in September 2011. With the default settings – not utilizing frameworks – Cocoapods would compile the third-party code and merge it with your individual, leading to a single monolithic app binary. And naturally it might handle all these Goal-C headers for you. For those who added use_frameworks! to your Podfile then the technique would change to as a substitute create a framework/module per pod/library. And that will be the requirement for whenever you had been utilizing exterior libraries written in Swift, or so I assumed …
I’ve all the time used that in apps I’m engaged on which use Cocoapods for dependencies. Think about me rambling on to a shopper of mine concerning the disadvantages of dynamic frameworks, making an attempt to persuade him of the advantages of Swift Bundle Supervisor. Think about my shock once we inspected his app’s bundle, solely to seek out however a single framework in there. All of the third occasion code he had ended up fused with the app binary, my library – written in Swift and built-in by way of git submodule and Xcode sub venture – leading to the one dynamic framework in his app.
By default, CocoaPods had been doing all alongside what we all know to be the smarter selection: if third occasion code is obtainable, to merge the thing code it into the app binary. After all closed-source frameworks that are solely obtainable as dynamic framework binaries go away you with out this feature. Personally I attempt to keep away from these, just like the satan avoids holy water.
Oh and I additionally would be the first to confess that I might by no means heat myself to Carthage. I’ve by no means checked out it. So far as I perceive, the distinction in strategy versus CocoaPods is that Carthage solely wants a repo URL so as to add a element, whereas CocoaPods wants a Podspec and can generate an Xcode workspace for you the place all dependencies are arrange in a Pods venture. I imagine it could be this workspace wizardry which may put some folks off Cocoapods.
Resourceful Swift Packages
Earlier than the present model 5.3 of SPM the 2 huge remaining ache factors have been the dearth of dealing with of sources and no assist for distributing binaries as packages. These have now been remedied and what’s the very best half is that Swift packages now have correct integration in Xcode 12.
One other huge benefit that CocoaPods had over different dependency managers was the existence of the “trunk”, a centralised repository of accessible pods. There you can search and discover libraries that will fulfil sure wants of yours. One other necessary side can be that for a model to be launched on the CocoaPods trunk, you would need to “lint” your pod spec which might validate the syntax and make it possible for the library builds with out errors or warnings.
Apple (and the SwiftPM open supply neighborhood) have labored on sharpening the software itself. However the central repository with validation side of package deal administration was unfilled. Till Dave Verver stepped and established the Swift Bundle Index. In his personal phrases:
The Swift Bundle Index is a search engine for packages that assist the Swift Bundle Supervisor.
However this web site isn’t merely a search software. Choosing the proper dependencies is about extra than simply discovering code that does what you want. Are the libraries you’re selecting nicely maintained? How lengthy have they been in improvement? Are they nicely examined? Choosing high-quality packages is difficult, and the Swift Bundle Index helps you make higher choices about your dependencies.
Dave launched the SwiftPM Library within the fall of 2019 which in June 2020 obtained re-engineered because the Swift Bundle Index which we use at the moment.
It was this implementation of a central index, focussing on package deal high quality, that pushed me over the sting to lastly begin embracing SPM. With CocoaPods it has been a tedium to arrange a CI server to maintain constructing your libraries for each change to make it possible for nothing breaks. In contrast, SPI builds your package deal with Swift variations 4.0, 5.0, 5.1, 5.2, 5.3 for iOS, macOS Intel, macOS ARM, Linux, tvOS and watchOS and can then present on the package deal’s web page the place that labored.
This web page offers a really good overview by which builders can acquire an concept as to the standard of this library. And for us venture homeowners it gives an incentive to attempt to maximise the variety of inexperienced checkmarks you see.
SPI nonetheless tracks 5.3 as “beta” though Xcode 12 has gone gold a month in the past. The reason is that Apple has rushed out Xcode 12 and the finalised assist for constructing common apps that may additionally run on Apple Silicon can be in Xcode 12.2 – obtainable later this yr.
I additionally like how SPI tracks each the most recent secure launch (by way of tag on grasp) in addition to the progress on the develop department. I needed for these builds to be coming sooner, ideally proper after pushing modifications to the GitHub repo, however generally it could actually take a very long time for the builds to be scheduled. Additionally a approach to retry a failed construct can be very good, as we’re used to from Travis-CI or GitLab-CI.
Conclusion
At this level I wished to enter the issues I realized so removed from including SPM to a few of my libraries, however I’m nonetheless preventing with SPI over a few of these coveted checkmarks. Additionally this text has already turned out longer than I wished it to, that I’ll try this within the subsequent one.
Let me know if that’s of curiosity to you, by dropping me a tweet. Are you contemplating including SPM your self? Which half did you wrestle with?
Half 2 is right here.
Additionally printed on Medium.
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