将使用除法步骤的C风格for循环转换为Swift 3

I have this loop, decrementing an integer by division, in Swift 2.

我有这个循环，在Swift 2中按分区递减整数。

for var i = 128; i >= 1 ; i = i/2  {
   //do some thing
}

The C-style for loop is deprecated, so how can I convert this to Swift 3.0?

不推荐使用C风格的for循环，那么如何将其转换为Swift 3.0呢？

3 个解决方案

#1

MartinR's solution is very generic and useful and should be part of your toolbox.

MartinR的解决方案非常通用且有用，应该是您工具箱的一部分。

Another approach is to rephrase what you want: the powers of two from 7 down to 0.

另一种方法是改写你想要的东西：2的幂从7下降到0。

for i in (0...7).reversed().map({ 1 << $0 }) {
    print(i)
}

#2

Quite general loops with a non-constant stride can be realized with sequence:

具有非常数步幅的相当一般循环可以通过序列实现：

for i in sequence(first: 128, next: { $0 >= 2 ? $0/2 : nil }) {
    print(i)
}

Advantages: The loop variable i is a constant and its scope is restricted to the loop body.
优点：循环变量i是常量，其范围仅限于循环体。
Possible disadvantages: The terminating condition must be adapted (here: $0 >= 2 instead of i >= 1), and the loop is always executed at least once, for the first value.
可能的缺点：必须调整终止条件（此处：$ 0> = 2而不是i> = 1），并且对于第一个值，循环始终至少执行一次。

One could also write a wrapper which resembles the C-style for loop more closely and does not have the listed disadvantages (inspired by Erica Sadun: Stateful loops and sequences):

人们还可以编写一个类似于C风格for循环的包装器，并且没有列出的缺点（受Erica Sadun启发：有状态循环和序列）：

public func sequence<T>(first: T, while condition: @escaping (T)-> Bool, next: @escaping (T) -> T) -> UnfoldSequence<T, T> {
    let nextState = { (state: inout T) -> T? in
        guard condition(state) else { return nil }
        defer { state = next(state) }
        return state
    }
    return sequence(state: first, next: nextState)
}

and then use it as

然后用它作为

for i in sequence(first: 128, while: { $0 >= 1 }, next: { $0 / 2 }) {
    print(i)
}

#3

I'll suggest that you should use a while loop to handle this scenario:

我建议你应该使用while循环来处理这种情况：

var i = 128
while i >= 1
{
    // Do your stuff
    i = i / 2
}

#1