In Swift 2 a String
is not a collection of anything. According to the documentation:
/// `String` is not itself a collection of anything. Instead, it has
/// properties that present the string's contents as meaningful
/// collections:
///
/// - `characters`: a collection of `Character` ([extended grapheme
/// cluster](http://www.unicode.org/glossary/#extended_grapheme_cluster))
/// elements, a unit of text that is meaningful to most humans.
///
/// - `unicodeScalars`: a collection of `UnicodeScalar` ([Unicode
/// scalar
/// values](http://www.unicode.org/glossary/#unicode_scalar_value))
/// the 21-bit codes that are the basic unit of Unicode. These
/// values are equivalent to UTF-32 code units.
///
/// - `utf16`: a collection of `UTF16.CodeUnit`, the 16-bit
/// elements of the string's UTF-16 encoding.
///
/// - `utf8`: a collection of `UTF8.CodeUnit`, the 8-bit
/// elements of the string's UTF-8 encoding.
Assuming you want to find the second character,
var str = "Hello, playground"
let chars = str.characters
let n = 2
let c = str.characters[str.characters.startIndex.advancedBy(n)]