这是合理的Objective-C块实现吗?

问题描述

我想要一个NSRegularExpression的– stringByReplacingMatchesInString:options:range:withTemplate:方法的变体，它采用一个块而不是一个模板.该块的返回值将用作替换值.可以想象，这比模板更灵活.有点像在Perl正则表达式中使用/e修饰符.

I wanted a variation of NSRegularExpression's – stringByReplacingMatchesInString:options:range:withTemplate: method that takes a block instead of a template. The return value of the block would be used as the replacement value. This is more flexible than a template, as you can imagine. Sort of like using the /e modifier in Perl regular expressions.

所以我写了一个类别来添加方法.这是我想出的:

So I wrote a category to add the method. This is what I came up with:

@implementation NSRegularExpression (Block)

- (NSString *)stringByReplacingMatchesInString:(NSString *)string
                                       options:(NSMatchingOptions)options
                                         range:(NSRange)range
                                    usingBlock:(NSString* (^)(NSTextCheckingResult *result))block
{
    NSMutableString *ret = [NSMutableString string];
    NSUInteger pos = 0;

    for (NSTextCheckingResult *res in [self matchesInString:string options:options range:range]) {
        if (res.range.location > pos) {
            [ret appendString:[string substringWithRange:NSMakeRange(pos, res.range.location - pos)]];
        }
        pos = res.range.location + res.range.length;
        [ret appendString:block(res)];
    }
    if (string.length > pos) {
        [ret appendString:[string substringFromIndex:pos]];
    }
    return ret;
}

@end

这是我第一次尝试在Objective C中玩积木.感觉有点奇怪，但似乎效果很好.我对此有几个疑问:

This is my first attempt to play with blocks in Objective C. It feels a little weird, but it seems to work well. I have a couple of questions about it, though:

1. 这似乎是实施这种方法的明智方法吗?
2. 是否有某种方法可以使用-enumerateMatchesInString:options:range:usingBlock:来实现其内部?我尝试过，但是无法从该块内分配给pos.但是，如果有一种方法可以使它起作用，那么也可以传递NSMatchingFlags和BOOL并以与该方法相同的方式处理它们，这很酷.可以吗?

1. Does this seem like a sane way to implement such a method?
2. Is there some way to implement its internals using -enumerateMatchesInString:options:range:usingBlock:? I tried it, but could not assign to pos from within the block. But if there was a way to make it work, it'd be cool to also pass the NSMatchingFlags and BOOL and handle them in the same way as that method. Do-able?

---

更新

感谢戴夫·德隆(Dave DeLong)的回答，我使用了一个新的代码块:

Thanks to the answer from Dave DeLong, I've got a new version using a block:

@implementation NSRegularExpression (Block)

- (NSString *)stringByReplacingMatchesInString:(NSString *)string
                                       options:(NSMatchingOptions)options
                                         range:(NSRange)range
                                    usingBlock:(NSString * (^)(NSTextCheckingResult *result, NSMatchingFlags flags, BOOL *stop))block
{
    NSMutableString *ret = [NSMutableString string];
    __block NSUInteger pos = 0;

    [self enumerateMatchesInString:string options:options range:range usingBlock:^(NSTextCheckingResult *match, NSMatchingFlags flags, BOOL *stop)
    {
        if (match.range.location > pos) {
            [ret appendString:[string substringWithRange:NSMakeRange(pos, match.range.location - pos)]];
        }
        pos = match.range.location + match.range.length;
        [ret appendString:block(match, flags, stop)];
    }];
    if (string.length > pos) {
        [ret appendString:[string substringFromIndex:pos]];
    }
    return [NSString stringWithString:ret];
}

@end

太棒了，谢谢！

推荐答案

能够从块内分配给pos就像将声明从以下位置更改一样简单:

Being able to assign to pos from within the block would be as simple as changing the declaration from:

NSUInteger pos = 0;

收件人:

__block NSUInteger pos = 0;

有关__block关键字的更多信息: __block变量

More info on the __block keyword: __block Variables

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