SPM-ifying YapDatabase

written by Mickey on 2020-10-18

Converting an existing Objective-C/Swift framework to Swift Package Manager

I'm a big fan of the database library YapDatabase, which is a collection/key/value store for macOS, iOS, tvOS & watchOS. It comes with many high level features and is built atop sqlite.

In the last 5 years, I have used this successfully for many of my projects. It is written in Objective-C and comes with a bunch of Swift files for more Swifty use. Since I recently announced to go all-in with Swift, I want to convert all my dependencies to the Swift Package Management system. I have never been a fan of CocoaPods or Carthage as I found them too invasive.

As this point of time though, YapDatabase is not Swift Package Manager (SPM) compatible and all approaches to do this using the current source layout did fail. So I had a fresh look at it and decided to do it slightly differently: If you don't have to work with the constraints of an existing tree layout, the process is relatively straightforward. Read on to find out what I did.

Prerequisites

• Use swift package init to create a package named YapDatabase.
• Edit Package.swift to make the package create two libraries with associated targets
  • ObjCYapDatabase is going to hold the Objective-C part in Sources/ObjCYapDatabase,
  • SwiftYapDatabase is going to hold the Swift parts in Sources/SwiftYapDatabase.

I couldn't name the Objective-C library simply YapDatabase, since this would have required to rename the (then umbrella) header file YapDatabase.h, which I didn't want to.

Swift vs. Objective-C

At the moment, SPM is not capable of handling mixed language targets, i.e., you either have only Swift files or no Swift files at all in your target – therefore I split the repository accordingly and moved Swift files below Sources/SwiftYapDatabase.

Source and Header file locations

SPM is pretty rigid when it comes to the location of source and header files. This is the reason why I unfortunately could not deliver this work on top of the original source repository.

Fortunately though, the source repository was very well structured. To layout the files in a way that makes SPM happy, I

• Created two header file directory, include for public headers, privateInclude for private headers.
• Moved all header files from Internal directories and those with private in their name to the privateInclude directory.
• Moved the remaining header files to the public include directory.

Swift

The aforementioned steps were enough to make SPM compile the ObjCYapDatabase. To make the Swift part compile, I had to

• Edit all Swift files to import ObjCYapDatabase instead of Foundation via sed -i -e s,Foundation,ObjCYapDatabase,g *.swift.

This made the SwiftYapDatabase compile.

What's Next

There are some parts missing: I didn't include the example programs, the tests, and the Xcode project.

I don't know Robbie Hanson's (creator of YapDatabase) plans. As it stands, this shuffling around was merely a proof-of-concept to find out whether such an approach is sufficient to SPM-ify YapDatabase or whether to there are more problems to consider. I will incorporate this in one of my projects to put it through a real world test.

I have published the repository as mickeyl/SwiftYapDatabase and will report this work via the YapDatabase issue tracker. Let's see what happens next.