数组范围迅速 [英] Array range for swift

问题描述

以下python代码的快速等效之处是什么?

What could be the swift equivalent of following python code ?

array =[ "a", "b", "c"]
print(array[1:])

(上面的语句打印从第一个索引到数组末尾的每个元素.
输出 ['b'，'c'])

( Above statement prints every element from first index upto end of array.
Output ['b', 'c'])

修改
有没有一种方法可以使用array.count来完成?由于array.count是多余的，如果我说要从第二个位置开始每个元素

Edit
Is there a way where this could be done with out using array.count ? Since the array.count is redundant if I say want every element from second position

推荐答案

您可以通过以下方式实现所需的目标:

You can achieve what you're looking for in the following way:

1..创建一个自定义结构来存储开始和结束索引.如果 startIndex 或 endIndex 为 nil ，这将表示该范围沿该方向无限扩展.

1. Create a custom struct to store a start and end index. If startIndex or endIndex is nil this will be taken to mean the range extends infinitely in that direction.

struct UnboundedRange<Index> {
    var startIndex, endIndex: Index?

    // Providing these initialisers prevents both `startIndex` and `endIndex` being `nil`.
    init(start: Index) {
        self.startIndex = start
    }

    init(end: Index) {
        self.endIndex = end
    }
}

2..在我的选择中，定义运算符以创建 BoundedRange ，因为必须使用初始化程序会导致一些相当难看的代码.

2. Define operators to create an BoundedRange as having to use the initialisers will lead to some quite unsightly code, in my option.

postfix operator ... {}
prefix  operator ... {}

postfix func ... <Index> (startIndex: Index) -> UnboundedRange<Index> {
    return UnboundedRange(start: startIndex)
}

prefix func ... <Index> (endIndex: Index) -> UnboundedRange<Index> {
    return UnboundedRange(end: endIndex)
}

一些用法示例:

1...  // An UnboundedRange<Int> that extends from 1 to infinity.
...10 // An UnboundedRange<Int> that extends from minus infinity to 10.

3..扩展 CollectionType ，以便它可以处理 UnboundedRange s.

3. Extend the CollectionType so it can handle UnboundedRanges.

extension CollectionType {
    subscript(subrange: UnboundedRange<Index>) -> SubSequence {
        let start = subrange.startIndex ?? self.startIndex
        let end = subrange.endIndex?.advancedBy(1) ?? self.endIndex
        return self[start..<end]
    }
}

4..要在给定的示例中使用它，请执行以下操作:

4. To use this in your given example:

let array = ["a", "b", "c"]

array[1...] // Returns ["b", "c"]
array[...1] // Returns ["a", "b"]

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