NSString+Additions.h

#import <Foundation/Foundation.h>

@interface NSString (Additions)

- (NSString *)stringByReplacingSubstringsAtRanges:(NSArray *) rangeValues
                                      withStrings:(NSArray *)strings;

@end

NSString+Additions.m

#import "NSString+Additions.h"

@implementation NSString (Additions)

- (NSString *)stringByReplacingSubstringsAtRanges:(NSArray *)rangeValues
                                      withStrings:(NSArray *)strings
{
    NSMutableString *resultCode = [[self mutableCopy] autorelease];
    SMAssert(([rangeValues count] == [strings count]), @"Number of ranges and string replacements should be equal");

    NSInteger diff = 0;
    NSRange replaceRange;
    NSString *replaceString;
    for (NSUInteger index =0; index < [rangeValues count]; index++)
    {
        replaceRange = [[rangeValues objectAtIndex:index] rangeValue];
        replaceRange.location += diff;

        replaceString = [strings objectAtIndex:index];
        [resultCode replaceCharactersInRange:replaceRange
                                  withString:replaceString];
        diff += [replaceString length] - replaceRange.length;
    }

    return resultCode;
}

@end