By doing optional chaining you can do something like: if let name = result.person?.firstName { ... } which only evaluates firstName if person is not nil, and then stores the result in name which is immutable.
It's easier to avoid mutable code in Swift than in many other languages. For this reason I would love to start working with Swift on the backend at some point in the future.
I like extensions, being able to extend any class I want by just typing it into any file I want. This helps with iterative development and trying something out.
Speaking of iteratively, if I want to try something quick, I can also drop down to a shell and start the Swift REPL to experiment.
I like how built-in functions like zip and mapValues are available, so it in some ways has a Pythonic feel. I like the syntax of building strings by just taking a variable name and going let s = "Hi there \(name)!".
There are lots of other things I enjoy, such as subscripts (see why here: https://docs.swift.org/swift-book/LanguageGuide/Subscripts.h...) and
Some things I would like to see improved is Xcode itself and also Swift's capabilities in the backend.
I've been waiting impatiently for a better Swift backend ecosystem, because I'd love to use it for web development as well.
- rich enums - (https://appventure.me/2015/10/17/advanced-practical-enum-exa...) Much of my code is now encapsulated in the enum, where it logically belongs, instead of distributed throughout some class that consumes the enum.
- highly expressive pattern matching - (https://appventure.me/2015/08/20/swift-pattern-matching-in-d...) Swift's pattern matching is especially powerful with a switch statement. I frequently bundle multiple values into a tuple and switch across them, which allows me to flatten many if-else pyramids, and makes control flow more obvious up front.
- Optional - (https://developer.apple.com/documentation/swift/optional)
- Protocol extensions - (https://docs.swift.org/swift-book/LanguageGuide/Extensions.h...) Other languages use things like abstract classes or traits to implement this behavior, but I find protocols to be much more composable.
- The standard library - Swift's standard library is really well thought out. Many standard types have been built on top of highly reusable (and easy to reason about) types or interfaces that provide enormous utility when I adopt them in my custom types. Examples of this are: Codable (https://developer.apple.com/documentation/foundation/archive...), Equatable and Hashable (https://developer.apple.com/documentation/swift/adopting_com...)
There's more than that, and Swift is definitely not without it's shortcomings, but those features have fundamentally changed how I reason about code. I frequently find myself wishing I could reach for similar tools in other languages.
Swift is a great language to work in.