How can I do a Swift for-in loop with a step?

The Swift synonym for a “step” is “stride” – the Strideable protocol in fact, implemented by many common numerical types.

The equivalent of (i = 1; i < max; i+=2) is:

for i in stride(from: 1, to: max, by: 2) {
    // Do something
}

Alternatively, to get the equivalent of i<=max, use the through variant:

for i in stride(from: 1, through: max, by: 2) {
    // Do something
}

Note that stride returns a StrideTo/StrideThrough, which conforms to Sequence, so anything you can do with a sequence, you can do with the result of a call to stride (ie map, forEach, filter, etc). For example:

stride(from: 1, to: max, by: 2).forEach { i in
    // Do something
}