How long is a reasonable amount of time to expect to learn Swift after being, say, quite rusty at C#?

Learning Swift, especially if you have a background in C# but are feeling rusty, can vary in time depending on several factors such as your prior programming experience, the amount of time you can dedicate to learning, and the resources you use. However, Swift is designed to be approachable for newcomers and powerful for experts, making it a relatively smooth transition for someone with prior programming experience.

Here are some key points from WWDC sessions that might help you gauge the learning curve:

1. Swift's Design and Features:

   • Swift is a modern programming language with a focus on performance and safety. It has a lightweight syntax that makes it enjoyable to program in and powerful features that can make you productive quickly (A Swift Tour: Explore Swift’s features and design).
   • Swift provides a lot of tools for abstraction that C# developers might find familiar, such as closures and generics, but with non-trivial implementations (Explore Swift performance).

2. Learning Resources and Community:

   • Swift has a strong community and a wealth of resources available, including the Swift Package Manager and a community-driven evolution process (What’s new in Swift).
   • Apple provides extensive documentation and sample projects, which can be very helpful for learning.

3. Practical Application and Migration:

   • If you are looking to migrate an existing app or start a new project, there are sessions like "Migrate your app to Swift 6" that provide practical guidance on adopting Swift and its concurrency model (Migrate your app to Swift 6).

4. Performance Considerations:

   • Understanding Swift's performance characteristics can be crucial, especially if you are coming from a language like C#. Swift has a powerful optimizer, and learning how to write performance-efficient code can be part of your learning journey (Explore Swift performance).

Given these points, a reasonable amount of time to become proficient in Swift could range from a few weeks to a few months, depending on your dedication and the complexity of the projects you undertake. Starting with basic tutorials and gradually moving to more complex projects while leveraging the community and resources provided by Apple can accelerate your learning process.