I have an incomplete understanding of functional programming. Are there other uses for closures (besides readability and practicality) that still work if they don't capture the value of i? If not, is this something someone should suggest as a change in swift-evolution?
Essentially it comes down to the semantics of `=` whether it's declaration or assignment. Swift appears to choose it to be assignment. If I remember right you can declare things constant which would effect declaration only (sort of) but clearly there's an expectation that this happens all the time.
Bindings rather than state, the author has no issue with captured objects being mutable, only with the captured environment being mutable.
Not sure why this "makes nonsense of the idea of a closure." You're closing over variables, not values. If you marked i using let instead of var, then you'd get the "preferred" behavior.
JavaScript also closes over variables, so it's not just "obscure" languages that behave this way.
Java only allows you to close over variables that are effectively final, to remove confusion on both sides (e.g. why doesn't the value in my closure change when I manipulate the original variable? vs. why does my the value in my closure change when I manipulate the original variable?)