Assigning an enumerator and it's reverse to a variable

Question

I'm stuck with this problem... I would like to enumerate in a regular for loop for one condition, and in reverse for another condition. Something like this:

var enumerator = 0..<length
if(stringPosition == .End) {
    enumerator = reverse(enumerator) //[C.Generator.Element] is not convertible to 'Range<Int>'
}
for index in enumerator {
    //do stuff
}

I'm getting a not convertible error there, and can't figure out how to proceed with that. I've tried different typecasting magic but that just doesn't work.

How should I sort out the conversion there?

score 1 · Accepted Answer · edited May 23 '17 at 12:27

1

Just casting to Array should work.

var enumerator = Array(0..<length) // <-- here
if(stringPosition == .End) {
    enumerator = reverse(enumerator)
    // then, enumerator.reverse() is better, I think
}
for index in enumerator {
    //do stuff
}

I think, more (memory) efficient way is like:

let range = lazy(0..<length)
let enumerator = stringPosition == .End ? SequenceOf(range.reverse()) : SequenceOf(range)
for index in enumerator {
    //do stuff
}

SequenceOf is a wrapper of any SequenceType. You can use this to store different sequence type to one variable.
for lazy(), see this answer or this.

edited May 23 '17 at 12:27

Community

1
1

answered Oct 15 '14 at 10:06

rintaro

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I would give you 2 upvotes, but I can only give you 1 :) great answer, thanks! – Marko Hlebar Oct 16 '14 at 06:16
1

Note that, the 2nd one is actually memory efficient, but much slower than 1st one. – rintaro Oct 16 '14 at 10:25

Assigning an enumerator and it's reverse to a variable

1 Answers1