chunk.swift

func chunk<T : Sliceable where T.Index : Strideable>(
    s: T,
    #from: T.Index,
    #to: T.Index,
    #by: T.Index.Stride
) -> GeneratorOf<T.SubSlice> {
    var g = stride(from: from, to: to, by: by).generate()
    return GeneratorOf<T.SubSlice> {
        if let start = g.next() {
            let end = start.advancedBy(by)
            var range = start ..< (end >= to ? to : end)
            return s[range]
        } else {
            return nil
        }
    }
}

// let a = [1, 2, 3, 4, 5, 6, 7, 8, 9, 10]
// let c = chunk(a, from: a.startIndex, to: a.endIndex, by: 3)
// for block in c {
//    println(block)
// }