Swift数组实例方法drop(at:Int)

问题描述

Swift中的Array 具有用于排除元素的几种实例方法，例如 dropFirst() ， dropLast() ， drop(while:) 等.drop(at:)怎么办?

注意:我会使用 remove(at:) ，但是我正在使用的数组是let常量.

Note: I'd use remove(at:), but the array I'm working with is a let constant.

推荐答案

您可以扩展RangeReplaceableCollection协议而不是Array类型，也可以在字符串上使用它:

You can extend RangeReplaceableCollection protocol instead of Array type, this way you can use it on Strings as well:

extension RangeReplaceableCollection {
    func drop(at offset: Int) -> SubSequence {
        let index = self.index(startIndex, offsetBy: offset, limitedBy: endIndex) ?? endIndex
        let next = self.index(index, offsetBy: 1, limitedBy: endIndex) ?? endIndex
        return self[..<index] + self[next...]
    }
}

---

var str = "Hello, playground"
str.drop(at: 5)  // "Hello playground"

---

let numbers = [1, 2, 3, 4, 5]
print(numbers.drop(at: 2))  // "[1, 2, 4, 5]\n"

---

如果您还希望在方法中接受String.Index:

---

If you would like to accept also String.Index in your method:

extension RangeReplaceableCollection {
    func drop(at index: Index) -> SubSequence {
        let index = self.index(startIndex, offsetBy: distance(from: startIndex, to: index), limitedBy: endIndex) ?? endIndex
        let next = self.index(index, offsetBy: 1, limitedBy: endIndex) ?? endIndex
        return self[..<index] + self[next...]
    }
}

---

var str = "Hello, playground"
str.drop(at: 0)               // "ello, playground"
str.drop(at: str.startIndex)  // "ello, playground"

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