Swift Pair Generator

ParingGenerator.swift

/*
* Allows iteration over pairs of a series
* This is useful for comparing or performing actions on
* adjacent items in an array
*/
struct PairingGenerator<Generator: GeneratorType>: GeneratorType {
    
    var generator: Generator
    var previous: Generator.Element?
    let first: Generator.Element?
    
    init(generator: Generator, looparound: Bool){
        self.generator = generator
        self.previous = self.generator.next()
        self.first = looparound ? previous : nil
    }
    
    mutating func next() -> (Generator.Element, Generator.Element)? {
        if let previous = previous, let next = self.generator.next() {
            let pair = (previous, next)
            self.previous = next
            return pair
        }
        else if let first = first, let previous = previous {
            self.previous = nil
            return (previous, first)
        }
        else {
            return nil
        }
    }
}

struct PairSequence<Sequence: SequenceType>: SequenceType {
    let sequence: Sequence
    let looparound: Bool
    
    init(sequence: Sequence, looparound: Bool = false){
        self.sequence = sequence
        self.looparound = looparound
    }
    
    func generate() -> PairingGenerator<Sequence.Generator> {
        return PairingGenerator(generator: sequence.generate(), looparound: looparound)
    }
}

extension SequenceType {
    func pairs(looparound: Bool = false) -> PairSequence<Self> {
        return PairSequence(sequence: sequence, looparound: looparound)
    }
}