Swift 3.0 iterate over String.Index range

If you want to traverse over the characters of a `String`, then instead of explicitly accessing the indices of the `String`, you could simply work with the [`CharacterView`](

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) of the `String`, which conforms to [`CollectionType`](

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), allowing you access to neat subsequencing methods such as `prefix(_:)` and so on.

/* traverse the characters of your string instance,
up to middle character of the string, where "middle"
will be rounded down for strings of an odd amount of
characters (e.g. 5 characters -> travers through 2) */
let m = "alpha"
for ch in m.characters.prefix(m.characters.count/2) {
print(ch, ch.dynamicType)
} /* a Character
l Character */

/* round odd division up instead */
for ch in m.characters.prefix((m.characters.count+1)/2) {
print(ch, ch.dynamicType)
} /* a Character
l Character
p Character */

If you'd like to treat the characters within the loop as strings, simply use `String(ch)` above.

---

With regard to your comment below: if you'd like to access a range of the `CharacterView`, you could easily implement your own extension of `CollectionType` (specified for when `Generator.Element` is `Character`) making use of both `prefix(_:)` and `suffix(_:)` to yield a sub-collection given e.g. a half-open (`from..<to`) range

/* for values to >= count, prefixed CharacterView will be suffixed until its end */
extension CollectionType where Generator.Element == Character {
func inHalfOpenRange(from: Int, to: Int) -> Self {
guard case let to = min(to, underestimateCount()) where from <= to else {
return self.prefix(0) as! Self
}
return self.prefix(to).suffix(to-from) as! Self
}
}

/* example */
let m = "0123456789"
for ch in m.characters.inHalfOpenRange(4, to: 8) {
print(ch) /* \ */
} /* 4 a (sub-collection) CharacterView
5
6
7 */