熊谷さんの https://t.co/VICPp6Pmbg を参考にしつつ、さっき書いた植木算ジェネレータをstruct化してみた。 #CodePiece #cswift

CodePiece.swift

struct UekizanGenerator<S: SequenceType, E where S.Generator.Element == E> : GeneratorType {
    typealias Element = E

    private let margin: E
    private var elementGenerator: S.Generator
    private var preserved: E?
    private var isMargin = false

    init(_ sources: S, margin: E) {
        self.margin = margin
        elementGenerator = sources.generate()
        preserved = elementGenerator.next()
    }

    mutating func next() -> E? {
        defer { isMargin = !isMargin }
        return isMargin ? getMargin() : getElement()
    }

    private func getMargin() -> E? {
        guard preserved != nil else { return nil }
        return margin
    }
    private mutating func getElement() -> E? {
        defer { preserved = elementGenerator.next() }
        return preserved
    }
}

let gen = UekizanGenerator([10, 20, 30], margin: 7)
let sequence = AnySequence { gen }
for i in sequence {
    print(i)
}

sequence.reduce(0, combine: +)