Decrement index in a loop after Swift C-style loops deprecated

问题

How would you express a decrementing indexed loop in Swift 3.0, where the syntax below is not valid any more?

for var index = 10 ; index > 0; index-=1{
   print(index)
}

// 10 9 8 7 6 5 4 3 2 1

回答1:

Here is an easier (and more Swifty) approach.

for i in (0 ..< 5).reversed() {
    print(i) // 4,3,2,1,0
}

let array = ["a", "b", "c", "d", "e"]
for element in array.reversed() {
    print(element) // e,d,c,b,a
}

array.reversed().forEach { print($0) } // e,d,c,b,a

print(Array(array.reversed())) // e,d,c,b,a

回答2:

C-style loops with a fixed increment or decrement can be replaced by stride():

for index in 10.stride(to: 0, by: -1) {
    print(index)
}

// 10 9 8 7 6 5 4 3 2 1

Use stride(to: ...) or stride(through: ...) depending on whether the last element should be included or not.

This is for Swift 2. The syntax changed (again) for Swift 3, see this answer.

回答3:

From swift 3.0, The stride(to:by:) method on Strideable has been replaced with a free function, stride(from:to:by:)

 for index in stride(from: 10, to: 0, by: -1){
      print(index)
 }

回答4:

You can use stride method:

10.stride(through: 0, by: -1).forEach { print($0) }

or classic while loop.

回答5:

If you still want to use this C-style loop, here is what you need:

let x = 10

infix operator ..> { associativity left }
func ..>(left: Int, right: Int) -> StrideTo<Int> {
    return stride(from: left, to: right, by: -1)
}

for i in x..>0 {
    print(i)
}

来源：https://stackoverflow.com/questions/35032182/decrement-index-in-a-loop-after-swift-c-style-loops-deprecated

标签

swift

for-loop

decrement