Replace specific words in NSString - objective-c

Question

what is the best way to get and replace specific words in string ?
for example I have
NSString * currentString = #"one {two}, thing {thing} good";
now I need find each {currentWord}
and apply function for it
[self replaceWord:currentWord]
then replace currentWord with result from function
-(NSString*)replaceWord:(NSString*)currentWord;

Answer 1

The following example shows how you can use NSRegularExpression and enumerateMatchesInString to accomplish the task. I have just used uppercaseString as function that replaces a word, but you can use your replaceWord method as well:
EDIT: The first version of my answer did not work correctly if the replaced words are
shorter or longer as the original words (thanks to Fabian Kreiser for noting that!) .
Now it should work correctly in all cases.
NSString *currentString = #"one {two}, thing {thing} good";
// Regular expression to find "word characters" enclosed by {...}:
NSRegularExpression *regex;
regex = [NSRegularExpression regularExpressionWithPattern:#"\\{(\\w+)\\}"
options:0
error:NULL];
NSMutableString *modifiedString = [currentString mutableCopy];
__block int offset = 0;
[regex enumerateMatchesInString:currentString
options:0
range:NSMakeRange(0, [currentString length])
usingBlock:^(NSTextCheckingResult *result, NSMatchingFlags flags, BOOL *stop) {
// range = location of the regex capture group "(\\w+)" in currentString:
NSRange range = [result rangeAtIndex:1];
// Adjust location for modifiedString:
range.location += offset;
// Get old word:
NSString *oldWord = [modifiedString substringWithRange:range];
// Compute new word:
// In your case, that would be
// NSString *newWord = [self replaceWord:oldWord];
NSString *newWord = [NSString stringWithFormat:#"--- %# ---", [oldWord uppercaseString] ];
// Replace new word in modifiedString:
[modifiedString replaceCharactersInRange:range withString:newWord];
// Update offset:
offset += [newWord length] - [oldWord length];
}
];
NSLog(#"%#", modifiedString);
Output:
one {--- TWO ---}, thing {--- THING ---} good