迭代器模式
oldbirds
# 迭代器模式
提供一种方法顺序访问一个聚合对象中各个元素, 而又无须暴露该对象的内部表示。
分离了集合对象的遍历行为,抽象出一个迭代器类来负责,这样既可以做到不暴露集合的内部结构,又可让外部代码透明地访问集合内部的数据。
# 样例
struct Book {
let name: String
let author: String
}
struct BookList: Sequence {
private let bookList: [Book]
init(books: [Book]) {
self.bookList = books
}
func makeIterator() -> BookListInterator {
return BookListInterator(books: bookList)
}
}
struct BookListInterator: IteratorProtocol {
typealias Element = Book
private var index = 0
private let books: [Element]
init(books: [Element]) {
self.books = books
}
mutating func next() -> Book? {
defer {
self.index += 1
}
return books.count > index ? books[index] : nil
}
}
let books = BookList(books: [
Book(name: "西游记", author: "吴承恩"),
Book(name: "三国演义", author: "罗贯中")
])
for book in books {
print("书籍:\(book.name) - \(book.author)")
}
结果显示:
书籍:西游记 - 吴承恩
书籍:三国演义 - 罗贯中