我们先看函数的原型：
public func split(separator: Self.Iterator.Element,maxSplits: Int = default,omittingEmptySubsequences: Bool = default) -> [Self.SubSequence]
第一个参数就不用解释了，传入要切割的字符串，像这样
let line = "BLANCHE: I don't want realism. I want magic!"
print(line.characters.split(separator: " ")
.map(String.init))
// Prints "["BLANCHE:","I","don\'t","want","realism.","magic!"]"
下面看第二个参数，像这样，意思是切割几次，设置为1的话就把原来的字符串切成两个。
// The second example passes `1` for the `maxSplits` parameter,so the
// original string is split just once,into two new strings.
print(line.characters.split(separator: " ",maxSplits: 1)
.map(String.init))
// Prints "["BLANCHE:"," I don\'t want realism. I want magic!"]"第三个参数就很明确了，是否保留隐藏字符
// The final example passes `false` for the `omittingEmptySubsequences`
// parameter,so the returned array contains empty strings where spaces
// were repeated.
print(line.characters.split(separator: " ",omittingEmptySubsequences: false)
.map(String.init))
// Prints "["BLANCHE:","","magic!"]"
看看官方文档对这三个参数的解释，懒得翻译了，也不是很难懂。
/// - Parameters: /// - separator: The element that should be split upon. /// - maxSplits: The maximum number of times to split the collection,or /// one less than the number of subsequences to return. If /// `maxSplits + 1` subsequences are returned,the last one is a suffix /// of the original collection containing the remaining elements. /// `maxSplits` must be greater than or equal to zero. The default value /// is `Int.max`. /// - omittingEmptySubsequences: If `false`,an empty subsequence is /// returned in the result for each consecutive pair of `separator` /// elements in the collection and for each instance of `separator` at /// the start or end of the collection. If `true`,only nonempty /// subsequences are returned. The default value is `true`. /// - Returns: An array of subsequences,split from this collection's /// elements.原文链接：https://www.f2er.com/swift/321952.html
