Swift Code, Compatible with Objective-C

Despite the fact that Apple have provided us with detailed documentation on how to use Swift code inside Objective-C application (and vice versa), it doesn’t fell enough when it actually comes to it. When I had to provide a Swift framework with Objective-C compatibility, Apple documentation raised more questions than gave answers (or at least left many gaps). Intensive search proved that the subject is lit quite poorly: a couple of questions on StackOverflow and some introductory articles — that’s all I’d found.

This post is the summary of the information I found and my own experience. All described methods don’t claim to be good practices, they just offer a way to solve the problem.

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TL;DR. In order to use Swift code inside Objective-C one must scrifice some Swift features and write a wrapper around original Swift code that won’t use non-compatible features (like structs, generics, enum associated values, protocol extensions etc.). All wrapper classes must inherit from NSObject.

The Beginning

So, we have an Objective-C-based project and a Swift module. To make it visible from Objective-C code there’s no need in using import of entire module (as we’re used to do in Swift), nor of single files (as we’re used to do in Objective-C)…