是否可以编写一个 Swift 函数来仅替换像 ‍‍‍ 这样的扩展字素簇的一部分？

Question

我想写一个可以像这样使用的函数：

let ‍‍‍ = "‍‍‍".replacingFirstOccurrence(of: "", with: "")

鉴于，这在 Swift 中可能吗？

Answer 1

根据在获得的见解，一个明智的方法可能是替换 Unicode 标量：

extension String {
    func replacingFirstOccurrence(of target: UnicodeScalar, with replacement: UnicodeScalar) -> String {

        let uc = self.unicodeScalars
        guard let idx = uc.index(of: target) else { return self }
        let prefix = uc[uc.startIndex..<idx]
        let suffix = uc[uc.index(after: idx) ..< uc.endIndex]
        return "\(prefix)\(replacement)\(suffix)"
    }
}

示例：

let family1 = "‍‍‍"
print(family1.characters.map { Array(String([=11=]).unicodeScalars) })
// [["\u{0001F469}", "\u{200D}"], ["\u{0001F469}", "\u{200D}"], ["\u{0001F467}", "\u{200D}"], ["\u{0001F466}"]]

let family2 = family1.replacingFirstOccurrence(of: "", with: "")
print(family2) // ‍‍‍
print(family2.characters.map { Array(String([=11=]).unicodeScalars) })
// [["\u{0001F469}", "\u{200D}"], ["\u{0001F469}", "\u{200D}"], ["\u{0001F466}", "\u{200D}"], ["\u{0001F466}"]]

这是一个可能的版本，它定位并替换任意字符串的 Unicode 标量：

extension String {
    func replacingFirstOccurrence(of target: String, with replacement: String) -> String {
        let uc = self.unicodeScalars
        let tuc = target.unicodeScalars

        // Target empty or too long:
        if tuc.count == 0 || tuc.count > uc.count {
            return self
        }

        // Current search position:
        var pos = uc.startIndex
        // Last possible position of `tuc` within `uc`:
        let end = uc.index(uc.endIndex, offsetBy: tuc.count - 1)

        // Locate first Unicode scalar
        while let from = uc[pos..<end].index(of: tuc.first!) {
            // Compare all Unicode scalars:
            let to = uc.index(from, offsetBy: tuc.count)
            if !zip(uc[from..<to], tuc).contains(where: { [=12=] !=  }) {
                let prefix = uc[uc.startIndex..<from]
                let suffix = uc[to ..< uc.endIndex]
                return "\(prefix)\(replacement)\(suffix)"
            }
            // Next search position:
            uc.formIndex(after: &pos)
        }

        // Target not found.
        return self
    }
}

Answer 2

使用 range(of:options:range:locale:) 解决方案变得非常简洁：

extension String {
    func replaceFirstOccurrence(of searchString: String, with replacementString: String) -> String {
        guard let range = self.range(of: searchString, options: .literal) else { return self }
        return self.replacingCharacters(in: range, with: replacementString)
    }
}

首先在实例中找到 searchString 的范围，如果找到范围，则将范围替换为 replacementString。否则实例只是 returns 本身。而且，由于 range(of:) 方法 returns 一旦找到匹配项，返回的范围保证是第一次出现。

"221".replaceFirstOccurrence(of: "2", with: "3")                // 321
"‍‍‍".replaceFirstOccurrence(of: "\u{1f469}", with: "\u{1f468}") // ‍‍‍

^{*澄清一下，最后一个测试用例将 woman-woman-girl-boy 转换为 man-woman-girl-boy.}

是否可以编写一个 Swift 函数来仅替换像 ‍‍‍ 这样的扩展字素簇的一部分？

Is it possible to write a Swift function that replaces only part of an extended grapheme cluster like ‍‍‍?

string

replace

unicode-string

emoji

swift