Passion Project: Mixing C++, Objective-C++, and Swift

I know a lot of folks have had to go through the process of bridging to C++ so you can use it from Objective-C or Swift. In my case I’m using it from Swift, so I thought I’d share what the middle Objective-C++ layer looks like. If you’ve done any Objective-C it will look like straight Objective-C, until you look a little closer. That’s when you’ll notice a C++ namespace, new, and delete statement. This code is a straight passthrough to the underlying C++ code — it’s here so Swift code can communicate with the C++ code.

Here’s the code that bridges to our Creatinine Clearance calculation.

View the code on Gist.

You’ll notice a class called PKMConvert that has a class method called genderFromPKMGender. I created a set of mirror enums. One on the iOS side the enums use NS_ENUM syntax, on the C++ side they’re straight C style enums, so this code converts between the two. It’s just a simple mapping.

Another thing you’ll notice is I’m still using “old” C++ syntax to create and destroy objects. I’ve been thinking about updating the syntax to C++11 so I’d use unique_ptr instead. We’ll see if that happens. It’s not a big deal.

Something I’ve been mulling over is releasing the entire PKMath C++ Library as an open source project once I have it working for iOS/Mac, Android, and Windows. I don’t know that it would be overly useful for anyone, but there you go.

Since I haven’t actually written any Swift code in the new RxCalc to use the Objective-C++ code I thought I’d share one of my unit tests for the Creatinine Clearance example above.

View the code on Gist.

Here’s how the different layers look from 30,000 feet. I like pictures, don’t you?