Getting C-level performance in Swift for numerical algorithms is quirky but not particularly difficult. If you limit yourself to value types (no classes or existentials), use unsafe pointers and tuples instead of arrays, use overflow discarding operators &+/&-/&* instead of normal +/-/*, use while or repeat/while for your loops, then Swift and clang C will generally compile to identical instructions.
I really recommend reading how Maxim made his FlatBuffer library 10 thousand times faster Swift.
“Teaching C” is really nice write up on what to teach in a C class. It has been a while since I was a student in University but there are some important points that I would have loved to know at that time. I think C is a much better language that people usually says, but the shortcomings make it have really bad publicity. If teachers can do a good job when teaching newcomers maybe we would not be creating software with such a poor performance and quality, and accepting it as a normal thing.
That’s the reason why I have to wait 30 seconds for Word to boot.
The author of the linked post gives some reasons on why Swift is a good language for an introduction to computer science class. I’m really interested in Swift being a good language to teach and I found the post really interesting.