NSString+Inflections

NSString+Inflections.m

// Inspired by suggestion to use NSScanner: http://stackoverflow.com/questions/1918972/camelcase-to-underscores-and-back-in-objective-c

#import "NSString+Inflections.h"

@implementation NSString (Inflections)

- (NSString *)underscore
{
    NSScanner *scanner = [NSScanner scannerWithString:self];
    scanner.caseSensitive = YES;

    NSCharacterSet *uppercase = [NSCharacterSet uppercaseLetterCharacterSet];
    NSCharacterSet *lowercase = [NSCharacterSet lowercaseLetterCharacterSet];

    NSString *buffer = nil;
    NSMutableString *output = [NSMutableString string];

    while (scanner.isAtEnd == NO) {

        if ([scanner scanCharactersFromSet:uppercase intoString:&buffer]) {
            [output appendString:[buffer lowercaseString]];
        }

        if ([scanner scanCharactersFromSet:lowercase intoString:&buffer]) {
            [output appendString:buffer];
            if (!scanner.isAtEnd)
                [output appendString:@"_"];
        }
    }
    
    return [NSString stringWithString:output];
}

- (NSString *)camelcase
{
    NSArray *components = [self componentsSeparatedByString:@"_"];
    NSMutableString *output = [NSMutableString string];

    for (NSUInteger i = 0; i < components.count; i++) {
        if (i == 0) {
            [output appendString:components[i]];
        } else {
            [output appendString:[components[i] capitalizedString]];
        }
    }

    return [NSString stringWithString:output];
}

- (NSString *)classify
{
    return [[self camelcase] capitalizedString];
}

@end

Pretty nice, but the method does not work, since -capitalizedString converts a string like "camelCase" to "Camelcase"
This should fix it:

- (NSString *)classify
{
    NSString *camelcase = [self camelcase];
    return [camelcase stringByReplacingCharactersInRange:NSMakeRange(0, 1) withString:[[camelcase substringWithRange:NSMakeRange(0, 1)] uppercaseString]];
}