好就没水文章了,水一波.😁😁😁

import Foundation

  

print("Hello, World!")

  

//protocol IteratorProtocol {

// associatedtype Element

// mutating func next() -> Element?

//}

  

struct Ones: IteratorProtocol {

 typealias Element = Int

 mutating func next() -> Int? {

 return 1

 }

}

  

var ones = Ones()

print(ones.next())

print(ones.next())

  

//struct Fibonacci: IteratorProtocol {

// typealias Element = Int

//

// private var state = (0, 1)

//

// mutating func next() -> Int? {

// let nextNumber = state.0

// state = (state.1, state.0 + state.1)

// return nextNumber

// }

//

//}

  

//var fibonacci = Fibonacci()

//print(fibonacci.next())

//print(fibonacci.next())

//print(fibonacci.next())

//print(fibonacci.next())

//print(fibonacci.next())

//print(fibonacci.next())

//

//var fibonacci1 = fibonacci

//print(fibonacci1.next())

  

//protocol Sequence {

// associatedtype Element

// associatedtype Iterator: IteratorProtocol where Iterator.Element == Element

//

// func makeIterator() -> Iterator

//}

  

struct FiboIter: IteratorProtocol {

 typealias Element = Int

 var state = (0, 1)

 mutating func next() -> Int? {

 let nextNumber = state.0

 self.state = (state.1, state.0 + state.1)

 return nextNumber

 }

}

  

struct Fibonacci: Sequence {

 typealias Element = Int

 func makeIterator() -> FiboIter {

 return FiboIter()

 }

}

  

var fibs = Fibonacci()

var fib1 = fibs.makeIterator()

print(fib1.next())

print(fib1.next())

print(fib1.next())

print(fib1.next())

print(fib1.next())

print(fib1.next())

print(fib1.next())

  

for n in  Fibonacci() {

 if n <= 5 {

 print(n)

 } else {

 break

 }

}

  

var arrayInt: [Int] = []

var sumInt = arrayInt.reduce(0, +)

print(sumInt)

  

var arrStr: [String] = []

var sumStr = arrStr.reduce("", +)

print(sumStr)

  

func reduce1(of sequence: S, _ partical: (E, E) -> E) -> E?

 where S: Sequence, E == S.Element {

 var iter: S.Iterator = sequence.makeIterator()

 guard var accumulated = iter.next() else {

 return nil

 }

 while let element = iter.next() {

 accumulated = partical(accumulated, element)

 }

 return accumulated

}

  

extension  Sequence {

 //FixedWidthInteger, SignedInteger , 先就这么着吧,🙂

 func reduceFromZero(of sequence: S, _ partical: (E, E) -> E) -> E where S: Sequence, E: FixedWidthInteger, E: SignedInteger, E == S.Element {

 var iter = sequence.makeIterator()

 guard var accumulated = iter.next() else { return 0 }

 while let element = iter.next() {

 accumulated = partical(accumulated, element)

 }

 return accumulated

 }

}

  

print(reduce1(of: arrayInt, +))

  

print([1].elementsEqual([1]))

--EOF--