NSString Category Methods Question

Question

I'm trying to put together an NSString category to handle a bunch of common string transformations I'm familiar with from working with AppleScript. I've got a few methods working but I'm stumbling over the following code. It would be easier if the NSScanner actually recorded whitespace characters but I don't see how to make that happen. So below is what I tried to do to compensate:
<pre>- (NSString *)stringByRemovingCharactersInSet:(NSCharacterSet *)removeSet {
BOOL scanned; // tracks if each looped scan gets anything
NSCharacterSet *whitespace = [NSCharacterSet whitespaceAndNewlineCharacterSet];
NSString *scannedString = [NSString string]; // to hold the resulting string
NSString *tmp, *whitespacePrefix, *remainingString = [NSString stringWithString:self]; // enumeration vars
NSRange whiteRange;
NSScanner *scanner = [NSScanner scannerWithString:self];
int scanIndex = 0;
while (!(scanIndex == [self length])) {
whiteRange = [remainingString rangeOfCharacterFromSet:whitespace options:NSLiteralSearch]; // check for whitespace prefix first
if (whiteRange.location == 0) { // and if exists store it in whitespacePrefix
whitespacePrefix = [remainingString stringWithPrefixCharactersInSet:whitespace];
scanIndex += [whitespacePrefix length]; // use the length of the whitespacePrefix to adjust scanner's scanLocation
scannedString = [scannedString stringByAppendingString:whitespacePrefix]; // and append whitespacePrefix to scannedString
[scanner setScanLocation:scanIndex];
scanned = [scanner scanUpToCharactersFromSet:removeSet intoString:&tmp];
if (scanned) {
scannedString = [scannedString stringByAppendingString:tmp];
scanIndex += [tmp length];
} else {
scanIndex++;
remainingString = [self substringWithRange:NSMakeRange(scanIndex, [self length] - scanIndex)]; // adjust remainingString
return scannedString;
- (NSString *)stringWithPrefixCharactersInSet:(NSCharacterSet *)prefixSet {
NSString *remainingString, *prefixString = [NSString string];
int s, e, i = 0;
NSRange prefixRange;
remainingString = [NSString stringWithString:self];
while (!(i == [self length])) {
prefixRange = [remainingString rangeOfCharacterFromSet:prefixSet options:NSLiteralSearch];
if (prefixRange.location == NSNotFound) {
break;
} else {
s = prefixRange.location;
e = prefixRange.length; // this should always be 1
if (s == 0) {
prefixString = [prefixString stringByAppendingString:[remainingString substringWithRange:NSMakeRange(s, e)]];
remainingString = [remainingString substringWithRange:NSMakeRange(s + e, [remainingString length] - e)];
} else break;
return prefixString;
}</pre>
Now, this obviously won't work in cases where you want to get rid of the whitespace but I could always make another method with a preserveWhitespace boolean argument, though I don't like this idea. Or I could check if whitespaceAndNewlineCharacterSet intersects with the removeSet and if so, avoid appending the whitespacePrefix to the scannedString but I have two problems with that: I don't want to bother with an NSMutableCharacterSet to get the intersection and, more importantly, I don't know how to check for an empty intersected character set, though I suspect if might be as easy as: if (!intersectedSet). And what if not all of the whitespaceAndNewline characters are in the removeSet, how would I determine which ones are in there? Okay, I guess that's three problems.
Is this kind of method more easily handled some other way? Don't bring up anything to do with regular expressions, though. I'm still not ready for that .
Also, for bonus points, I was thinking about a method that returns two values like NSFileManager's fileExistsAtPath:isDirectory: but I have no idea how to do that and I can't find any example code. I'm hoping to consolidate checking if the string has a prefix made of characters in a passed character set and if so the prefix string that would include any of those characters. Something like:
<pre>- (BOOL)hasPrefixWithCharactersInSet:(NSCharacterSet *)checkSet prefixString:(NSString **)resultString;</pre>
But how do I return two values in the method?
Also note: I have virtually no programming experience, so if I've made some terrible coding errors above, be gentle with me.
iMac G5 20"   Mac OS X (10.4.5)  

Answer 1

could you tell me how did you solve the problem?