It's been adopted like crazy. I can't imagine new projects being started in Objective-C. Certainly, I'd never join such a project, for sure. I think the rapid

It's been adopted like crazy. I can't imagine new projects being started in Objective-C. Certainly, I'd never join such a project, for sure. I think the rapid adoption is because you can basically just inherit any Objective-C class in Swift, and then add functionality. And that's just one way of mixing Swift into an existing code base, there are others.