Swift字符串扩展报错：Range初始化要求String.Index符合Strideable

我想给Swift的String类实现一个仿Python风格的替换函数（支持指定待替换字符串、替换字符串、替换次数），找到了@rmaddy开发的扩展代码，但添加到Xcode项目时出现错误：

Referencing initializer 'init(_:)' on 'Range' requires that 'String.Index' conform to 'Strideable'

原代码如下：

//Developed by rmaddy @ https://stackoverflow.com/users/2303865/rmaddy

extension String {
    func replacingOccurrences<Target, Replacement>(of target: Target, with replacement: Replacement, count: Int, options: String.CompareOptions = [], range searchRange: Range<String.Index>? = nil) -> String where Target : StringProtocol, Replacement : StringProtocol {
        var matches = [Range<String.Index>]()
        
        //This is where I get the error
        var sRange = searchRange ?? Range(startIndex..<endIndex)
        
        
        while matches.count < count && !sRange.isEmpty {
            if let mRange = range(of: target, options: options, range: sRange, locale: nil) {
                matches.append(mRange)
                if options.contains(.backwards) {
                    sRange = Range(sRange.lowerBound..<mRange.lowerBound)
                } else {
                    sRange = Range(mRange.upperBound..<sRange.upperBound)
                }
            } else {
                break
            }
        }
        
        var res = self
        for range in matches.sorted(by: { $0.lowerBound > $1.lowerBound }) {
            res.replaceSubrange(range, with: replacement)
        }
        return res
    }
}

问题原因与修复方案 #

错误根源在于：Swift的String.Index不遵循Strideable协议，因此不能通过Range()初始化器构造基于String.Index的范围。只需移除所有多余的Range()包装，直接使用半开范围表达式即可。

修改后的可用代码：

//Developed by rmaddy
extension String {
    func replacingOccurrences<Target, Replacement>(of target: Target, with replacement: Replacement, count: Int, options: String.CompareOptions = [], range searchRange: Range<String.Index>? = nil) -> String where Target : StringProtocol, Replacement : StringProtocol {
        var matches = [Range<String.Index>]()
        
        // 直接使用范围表达式，无需Range()包装
        var sRange = searchRange ?? startIndex..<endIndex
        
        while matches.count < count && !sRange.isEmpty {
            if let mRange = range(of: target, options: options, range: sRange, locale: nil) {
                matches.append(mRange)
                if options.contains(.backwards) {
                    sRange = sRange.lowerBound..<mRange.lowerBound
                } else {
                    sRange = mRange.upperBound..<sRange.upperBound
                }
            } else {
                break
            }
        }
        
        var res = self
        // 倒序替换避免索引偏移问题
        for range in matches.sorted(by: { $0.lowerBound > $1.lowerBound }) {
            res.replaceSubrange(range, with: replacement)
        }
        return res
    }
}

使用示例 #

let originalText = "He said hello, she said goodbye, they said hi"
// 替换前2次"said"为"exclaimed"
let modifiedText = originalText.replacingOccurrences(of: "said", with: "exclaimed", count: 2)
// 输出结果："He exclaimed hello, she exclaimed goodbye, they said hi"

内容的提问来源于stack exchange，提问作者Eme Campuzano