試圖從工作Iterator模式

Question

這裏獲得通用代碼是正常工作的代碼，這是實現迭代器模式的：

這裏是我認爲是由於的通用變化的代碼以上，但我有兩個錯誤代碼（見下面的代碼）：

struct Whatevers<T> { 
    let whatevers: [T] 
} 

extension Whatevers: Sequence { 
    func makeIterator() -> Whatevers<T>.Iterator { 
     return WhateversIterator(sequence: whatevers, current: 0) 
    } 
} 


struct WhateversIterator<T>: IteratorProtocol { 
    let sequence: [T] 
    var current = 0 

    mutating func next() -> WhateversIterator.Element? { 
     defer { current += 1 } 
     return sequence.count > current ? sequence[current] : nil 
    } 
} 

error: MyPlayground.playground:854:1: error: type 'Whatevers' does not conform to protocol 'Sequence' extension Whatevers: Sequence { ^

error: MyPlayground.playground:861:8: error: type 'WhateversIterator' does not conform to protocol 'IteratorProtocol' struct WhateversIterator: IteratorProtocol {

有人能解釋什麼是這個代碼不正確。我怎樣才能使它工作？

Answer 1

找到解決方案！

struct Whatevers<T> { 
    let whatevers: [T] 
} 

extension Whatevers: Sequence { 

    func makeIterator() -> WhateversIterator<T> { 
     return WhateversIterator(sequence: whatevers, current: 0) 
    } 
} 


struct WhateversIterator<T>: IteratorProtocol { 
    let sequence: [T] 
    var current = 0 

    mutating func next() -> T? { 
     defer { current += 1 } 
     return sequence.count > current ? sequence[current] : nil 
    } 
} 

所有的錯誤都來自功能makeIterator和下一個返回類型。

希望有人會發現它有幫助！