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swiftfor-loopdecrement
netshark1000
netshark1000

Reputation: 7413

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

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

Upvotes: 46

Views: 27530

Answers (5)

Bhavin Bhadani
Bhavin Bhadani

Reputation: 22374

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)
}

// You can also use stride condition like
// {Some Value}.stride(to: 0, by: -1)
// for index in 10.stride(to: 0, by: -1) { }

Upvotes: 33

Jonny
Jonny

Reputation: 2094

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

Upvotes: 62

Martin R
Martin R

Reputation: 539975

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.

Upvotes: 50

ielyamani
ielyamani

Reputation: 18591

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)
}

Upvotes: 1

Sebastian Osiński
Sebastian Osiński

Reputation: 3014

You can use stride method:

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

or classic while loop.

Upvotes: 10

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