您可以使用称为stride（to :, by :)的进度循环，每n个元素对元素进行一次迭代：
let array = Array(1...5)
let pairs = stride(from: 0, to: array.endIndex, by: 2).map {
(array[$0], $0 < array.index(before: array.endIndex) ? array[$0.advanced(by: 1)] : nil)
} // [(.0 1, {some 2}), (.0 3, {some 4}), (.0 5, nil)]
print(pairs) // "[(1, Optional(2)), (3, Optional(4)), (5, nil)]\n"
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