引用数组里面斯威夫特功能 [英] Reference to array inside function in Swift

问题描述

我想引用一个函数里的数组。结果
事情是这样的： A 和 B 是内部阵列秒。

I am trying to reference to an array inside a function.
Something like this: a and b are arrays of Ints.

  var inout refArr = &a
  if(!someFlag) {
     refArr = &b
  }
  refArr[someIndex] = 30

这不能编译，我只能用 INOUT 函数参数？
如果是这样，我该怎么做参考/指针的函数里面呢？

This does not compile, can I only use inout for function arguments? If so, how do I do a reference/pointer inside a function?

推荐答案

＆安培; 只能用来传递变量作为 INOUT 函数参数。所以，简单的解决方案可能是使用一个辅助功能
你的函数中：

& can only be used to pass a variable as an inout argument to a function. So the easiest solution is perhaps to use a helper function inside your function:

func foo() {

    func helper(inout array : [Int]) {
        array[2] = 99
    }

    var a = [1, 2, 3, 5, 6]
    var b = [4, 5, 6, 7]
    let someFlag = true

    if someFlag {
        helper(&a)
    } else {
        helper(&b)
    }

    // ...
}

您的可以的创建，使用 UnsafeMutableBufferPointer 数组的引用：

You can create a reference to the array using UnsafeMutableBufferPointer:

let ref = someFlag ?
    UnsafeMutableBufferPointer(start: &a, count: a.count) :
    UnsafeMutableBufferPointer(start: &b, count: b.count)
ref[2] = 99

但有两个问题的解决方案：

But there are two problems with this solution:

• UnsafeMutableBufferPointer（）创建一个非所属参考，
  所以编译器可能会决定释放而引用数组
  仍在使用。


• 没有界限的阵列上进行检查。

• UnsafeMutableBufferPointer() creates a non-owning reference, so the compiler might decide to deallocate the array while the reference is still used.
• There is no bounds check on the array.

因此​​，为了使这项工作安全，你必须添加一些code：

So to make this work safely, you have to add some code:

withExtendedLifetime(a) { () -> Void in
    withExtendedLifetime(b) { () -> Void in
        let ref = someFlag ?
            UnsafeMutableBufferPointer(start: &a, count: a.count) :
            UnsafeMutableBufferPointer(start: &b, count: b.count)
        if ref.count > 2 {
            ref[2] = 99
        }
    }
}

这是一个有点难看。

which is a bit ugly.

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