Reverse Range in Swift

Question

Is there a way to work with reverse ranges in Swift?

For example:

for i in 5...1 {
  // do something
}

is an infinite loop.

Answer 1

It appears that the answers to this question have changed a bit as we've progressed through the betas. As of beta 4, both the by() function and the ReversedRange type have been removed from the language. If you're looking to make a reversed range, your options are now as follows:

1: Create a forward range, and then use the reverse() function to reverse it.

for x in reverse(0 ... 4) {
    println(x) // 4, 3, 2, 1, 0
}

for x in reverse(0 ..< 4) {
    println(x) // 3, 2, 1, 0
}

2: Use the new stride() functions that were added in beta 4, which includes functions to specify the starting and ending indexes, as well as the amount to iterate by.

for x in stride(from: 0, through: -8, by: -2) {
    println(x) // 0, -2, -4, -6, -8
}

for x in stride(from: 6, to: -2, by: -4) {
    println(x) // 6, 2
}

Note that I've also included the new exclusive range operator in this post as well. .. was replaced with ..<.

Edit: From the Xcode 6 beta 5 release notes, Apple added the following suggestion for handling this:

ReverseRange has been removed; use lazy(x..

Here's an example.

for i in lazy(0...5).reverse() {
    // 0, 1, 2, 3, 4, 5
}