swift - 在 Swift 中的条件下删除集合的最后一个元素

Question

我试图从字符串数组的后面删除 "" & "" 直到最后一项包含一些文本，但我的实现没有开始""。

到目前为止我的实现:

var array = ["A", "B", "", "C", "D", " ", " ", ""]

while true {
    if (array.last == " " || array.last == "") {
        array.removeLast()
    } else {
        break
    }
}

我想要的输出是

["A", "B", "", "C", "D"]

，但我当前的输出是

["A", "B", "", "C", "D", " ", " "]

，while 循环在遇到 ""

后简单地 中断

有什么建议为什么它不接收 ""？

Answer 1

我不知道为什么他们有 drop(while:) 而没有实现 dropLast(while:)。下面的实现适用于任何集合:

extension Collection {
    func dropLast(while predicate: (Element) throws -> Bool) rethrows -> SubSequence {
        guard let index = try indices.reversed().first(where: { try !predicate(self[$0]) }) else {
            return self[startIndex..<startIndex]
        }
        return self[...index]
    }
}

---

"123".dropLast(while: \.isWholeNumber)    // ""
"abc123".dropLast(while: \.isWholeNumber) // "abc"
"123abc".dropLast(while: \.isWholeNumber) // "123abc"

并且扩展 RangeReplaceableCollection 我们还可以实现 remove(while:) 和 removeLast(while:):

extension RangeReplaceableCollection {
     mutating func remove(while predicate: (Element) throws -> Bool) rethrows {
        guard let index = try indices.first(where: { try !predicate(self[$0]) }) else {
            removeAll()
            return
        }
        removeSubrange(..<index)
    }
    mutating func removeLast(while predicate: (Element) throws -> Bool) rethrows {
        guard let index = try indices.reversed().first(where: { try !predicate(self[$0]) }) else {
            removeAll()
            return
        }
        removeSubrange(self.index(after: index)...)
    }
}

---

var string = "abc123"
string.removeLast(while: \.isWholeNumber)
string  // "abc"

var string2 = "abc123"
string2.remove(while: \.isLetter)
string2 // "123"

var array = ["A", "B", "", "C", "D", " ", " ", ""]
array.removeLast { $0 == "" || $0 == " " }
array  // ["A", "B", "", "C", "D"]