The Twenty-First Floor

Lately I've been following along on the Swift conversation about static and dynamic features and the importance of the dynamic runtime. I'd like to share some of my thoughts as a developer who is using both Swift and Objective-C on an almost daily basis.

The concept of using the right tool for the job is a bit of a cliché, but it describes my views on the static nature of Swift very well. I like that we as developers for Apple's platforms have great options on both ends of the spectrum. Swift is an excellent static language, and Objective-C and the associated dynamic runtime is a great tool as well. I haven't found myself only wanting to use one or the other.

Maybe the point of Swift is to have a strongly-typed static language to use for the things that should have compile time type checking, like building application layers. Having the capability to build your application in a type safe environment while still leveraging a sophisticated dynamic runtime that supports tools and behaviors that make our applications easier to build feels like a huge advantage to me.

I think Swift is a great language and I've been enjoying using it to build applications and internally used frameworks. A team I work with just shipped an app built entirely in Swift with a 0.0% crash rate. There's a lot of places where using a static language makes sense, and I'm not ready to judge Swift's future based on whether it could be used today to replicate UIKit, Core Data, or any other Cocoa frameworks.

The measure of Swift's success shouldn't be whether or not it eradicates Objective-C from our tool chain. Honestly, I don't think that it should. The value it is adding to our existing tool chain as a foundational component, and the capability it brings to build highly sophisticated and powerful tools like Interface Builder and Core Data earn it a place in our tool kit for a very long time to come.

I liked this quote from Manton's blog post about Apple's mindset on Swift dynamic features:

Remember when Steve Jobs came back to Apple and compared NeXTSTEP to constructing a building by starting out on the 20th floor, with so much of the foundation and common patterns already taken care of for you? Cocoa allowed apps to be built significantly faster than before. Steve said at Macworld Expo in 1997 that the goal was to “eliminate 80% of the code that every developer has to write for their app.”

I love this, because I think the building metaphor applies really well to where we are with Objective-C and Swift. The building is Cocoa, and we don't need to re-build the first 20 floors. What's great about the static nature of Swift is it gives developers an option to make that last 20% of code type safe, faster, and more expressive. For a lot of applications and use cases, that's a really great tool to have.


As a brief aside, I know that Swift has a lot of promise in areas with no history of a dynamic runtime, like Linux or perhaps even with embedded devices. I'm not trying to diminish that, or imply that Swift has to exist on top of Objective-C. I'm actually very excited about all of those areas and hope that Swift becomes widely used on other platforms. But I won't mind if much of the core platform for Mac and iOS continues to rely on the dynamic runtime.