Use Swift Code in Objective-C

When system X is written in Objective-C and system Y is written in Swift, only the API for system Y needs to be compatible with Objective-C. The key is to not tightly intermingle the two languages. But how do we achieve this if our new Swift code lives alongside our existing Objective-C code?

The goal is that the Swift code we write should be idiomatic Swift, following patterns that make sense in Swift. However, it's easy to end up with a 'halfway' Swift codebase that is difficult to work with and requires frequent refactoring efforts. We would create a situation where our model objects become classes for no reason, requiring a second refactoring pass to achieve our fully Swift vision.

In reality, even if we theoretically write the entire project in Swift, once we remove all the Objective-C code, none of the compromises we made will make sense anymore. Instead, we'll be left with an awkward point between an Objective-C and a fully Swift codebase.

When using value types for our model objects, we end up with classes that inherit from NSObject, enums that use Int as their raw value, and everything becomes optional. This approach is possible but may lead to suboptimal results. Value types, generics, enums with associated values, and optionals are all features of Swift that can be sacrificed for Objective-C interoperability.

Swift and Objective-C are interoperable, like a VHS player plugged into a 4K TV, but this doesn't mean we should sacrifice everything great about Swift to achieve compatibility. In our experience, it was difficult to integrate new Swift code into existing Objective-C classes and systems, and the results were minimal.

The initial approach of simply writing all new code in Swift may seem intuitive, but it's not always possible or practical. For example, rewriting a large codebase from scratch in Swift would take years. Instead, we need to find ways to integrate Swift and Objective-C more seamlessly.

In conclusion, using Swift code in Objective-C requires careful planning and consideration of the potential pitfalls. By understanding the limitations and challenges involved, we can create a smooth transition between our existing Objective-C codebase and a new Swift one.

Use swift code in objective c