Implementations of first() and last() functions in Swift.

untitled.swift

func first<S: Sequence> (seq: S) -> S.GeneratorType.Element? {
    var gen = seq.generate()
    return gen.next()
}

func first<S: Sequence> (seq: S, #count: Int) -> Slice<S.GeneratorType.Element> {
    var gen = seq.generate()
    var list = Slice<S.GeneratorType.Element>()
    
    while list.count < count {
        if let elem = gen.next() {
            list.append(elem)
        }
        else {
            break
        }
    }
    
    return list
}

func last<S: Sequence> (seq: S) -> S.GeneratorType.Element? {
    return reduce(seq, nil) { (_: S.GeneratorType.Element?, elem) in
        return elem
    }
}

func last<S: Sequence> (seq: S, #count: Int) -> Slice<S.GeneratorType.Element> {
    // IIRC, .removeAtIndex(0) is faster for Slice than Array;
    // if I'm wrong, you could replace Slice with Array with no change.
    return reduce(seq, Slice<S.GeneratorType.Element>()) { (var list, elem) in
        if list.count >= count {
            list.removeAtIndex(0)
        }
        list.append(elem)
        return list
    }
}