When you just really need both the current and next elements in a swift sequence

PeekAheadIterator.swift

import Foundation

struct PeekAheadIterator<T> {
	
	let elements:[T]

	public init(elements:[T]) {
		self.elements = elements
	}
	
	func each(closure:(T,T?)->Void) {
			
		var iterator = elements.makeIterator()
		var current  = iterator.next()
		var next     = iterator.next()
			
		while let current_ = current {
			closure(current_ , next)
			current = next
			next    = iterator.next()
		}
	}
}


let peekahead = PeekAheadIterator(elements: [1,2,3,4,5,6,7])
peekahead.each { current, next in
	print("\(current), \(next)")
}

/*
1, Optional(2)
2, Optional(3)
3, Optional(4)
4, Optional(5)
5, Optional(6)
6, Optional(7)
7, nil
*/