是否有 Objective-c 正则表达式替换为回调/C# MatchEvaluator 等效项？

Question

我有一个 C# 项目，打算移植到 Objective-C。根据我对 Obj-C 的了解，似乎存在各种令人困惑的正则表达式选项，但我看不到任何有关使用回调进行替换的方法。

我正在寻找相当于 C# MatchEvaluator 委托或 PHP 的 preg_replace_callback 的东西。我想在 C# 中做的一个例子是 -

// change input so each word is followed a number showing how many letters it has

string inputString = "Hello, how are you today ?";
Regex theRegex = new Regex(@"\w+");

string outputString = theRegex.Replace(inputString, delegate (Match thisMatch){
   return thisMatch.Value + thisMatch.Value.Length;
});

// outputString is now 'Hello5, how3 are3 you3 today5 ?'

我怎样才能在 Objective-C 中做到这一点？在我的实际情况中，正则表达式同时具有前向断言和后向断言，因此不幸的是，任何涉及提前查找字符串然后进行一系列直接字符串替换的替代方案都不起作用。

Answer 1

Foundation 有一个 NSRegularExpression 类（ iOS4 及更高版本），这可能对您有用。来自文档：

基本匹配方法
NSRegularExpression 是一个块
迭代器方法允许客户端
提供一个 Block 对象，它将是
每次定期调用
表达式匹配的一部分
目标字符串。还有额外的
返回所有内容的便捷方法
匹配作为数组，总数
比赛次数、第一场比赛、
以及第一个匹配的范围。

例如：

NSString *input = @"Hello, how are you today?";

// make a copy of the input string. we are going to edit this one as we iterate
NSMutableString *output = [NSMutableString stringWithString:input];

NSError *error = NULL;
NSRegularExpression *regex = [NSRegularExpression 
                                regularExpressionWithPattern:@"\\w+"
                                                     options:NSRegularExpressionCaseInsensitive 
                                                       error:&error];

// keep track of how many additional characters we've added (1 per iteration)
__block NSUInteger count = 0;  

[regex enumerateMatchesInString:input
                        options:0
                          range:NSMakeRange(0, [input length])
                     usingBlock:^(NSTextCheckingResult *match, NSMatchingFlags flags, BOOL *stop){

    // Note that Blocks in Objective C are basically closures
    // so they will keep a constant copy of variables that were in scope
    // when the block was declared
    // unless you prefix the variable with the __block qualifier

    // match.range is a C struct
    // match.range.location is the character offset of the match
    // match.range.length is the length of the match        

    NSString *matchedword = [input substringWithRange:match.range];

    // the matched word with the length appended
    NSString *new  = [matchedword stringByAppendingFormat:@"%d", [matchedword length]];

    // every iteration, the output string is getting longer
    // so we need to adjust the range that we are editing
    NSRange newrange = NSMakeRange(match.range.location+count, match.range.length);
    [output replaceCharactersInRange:newrange withString:new];

    count++;
}];
NSLog(@"%@", output); //output: Hello5, how3 are3 you3 today5?

Answer 2

我修改了 atshum 的代码，使其更加灵活：

__block int prevEndPosition = 0;
[regex enumerateMatchesInString:text
                        options:0
                          range:NSMakeRange(0, [text length])
                     usingBlock:^(NSTextCheckingResult *match, NSMatchingFlags flags, BOOL *stop)
{
    NSRange r = {.location = prevEndPosition, .length = match.range.location - prevEndPosition};

    // Copy everything without modification between previous replacement and new one
    [output appendString:[text substringWithRange:r]]; 
    // Append string to be replaced
    [output appendString:@"REPLACED"];

    prevEndPosition = match.range.location + match.range.length;
}];

// Finalize string end
NSRange r = {.location = prevEndPosition, .length = [text length] - prevEndPosition};
[output appendString:[text substringWithRange:r]];

现在似乎可以工作（可能需要更多测试）