It's a fully fledged programming language. An open-source programming language, at that, with a lot of community input and involvement.
Not a macOS or iOS app creation DSL.
It's also quite pleasant to use, and has already seen a few uses beyond macOS and iOS apps, including some backend development (Vapor, Kitura, SwiftNIO, probably others).
So you could use it to write command line tools. To write Linux or Windows apps. Or to write servers. Just like any other programming language.
Personally I have some significant experience with maybe 5 different languages, which is already more diverse than the average software dev as far as I know. But I still wouldn't be comfortable to judge something like this.
For instance, I haven't worked with Swift, but I find it hard to believe it's much better than, say, C#, Scala, or Typescript, regarding those metrics. Do you have experience in those languages?
It's subjective, naturally. I don't know if I'd be that enthusiastic, but I definitely like it a lot.
My main languages are Python and C++. I've also used Java, C#, Javascript but not Typescript, among others.
In my opinion Swift does a pretty good job at striking a balance between expressiveness/usability, safety and performance. If it gets more traction under Linux (including a larger ecosystem and better tooling around it) I'd definitely consider it for projects where Python could become a bottleneck but C++-level performance is not absolutely required.
On the other hand, other languages in a similar niche - Rust, Go, even D or Nim? are already more established outside of iOS/MacOS, so I don't know. My experience with Swift has definitely made me more interested in learning Rust, which seems quite similar in some respects.
Sounds like you describe the state of Swift at least three years ago. SourceKit just doesn't crash anymore on me anymore, ever. Compile times are quite good for me nowadays, still not as fast as Objective-C but then again you don't get compile time guarantees for free.
The exponential issue was still there in version 4 and I think 5 as well. Didn't say SourceKit crashed, but it was virtually useless because it functioned like a crap version of the language parser.
So what's particularly hard on the compiler are hard coded sets of data that have mixed types. For example a dictionary that reflects a JSON response that also has nested dictionaries.
It helps if you test declare it like:
let json: [String: Any] = [ /** lots of fields here */ ]
String concatenation: could you give me a specific piece of code that fails? It could be that I really never write code that triggers the problem. Using the + operator to concatenate strings has some performance issues though.
I'm not telling you're crazy, I just noticed that things got so much faster in the past two years.
The string concatenation issue was that if you do a ++ b ++ c... When that got to about 6 variables that single line alone took a minute to compile. Go to 10 variables and just give up on ever seeing a result. I used to try it in online Swift REPLs and it was still happening with whatever was most recent a bit over a year ago.
Not a macOS or iOS app creation DSL.
It's also quite pleasant to use, and has already seen a few uses beyond macOS and iOS apps, including some backend development (Vapor, Kitura, SwiftNIO, probably others).
So you could use it to write command line tools. To write Linux or Windows apps. Or to write servers. Just like any other programming language.