Question

here in my code i am trying to load a ROBOTS.TXT file and then filter them by “Disallow” string, then if that line has “Disallow string” delete this string and return the rest of line.

here is a sample of ROBOTS.TXT

User-agent: *

Disallow:/search

Disallow: /groups

Disallow: /images

Disallow: /catalogs

Allow: /catalogs/about

Disallow: /catalogues

Disallow: /news

Allow: /news/directory

and here is the code that i have :

NSRange range;
NSURL *url=[NSURL URLWithString:@"http://www.google.com/robots.txt"];

NSString *content = [NSString stringWithContentsOfURL:url encoding:NSUTF8StringEncoding error:nil];

NSArray *parsed = [content componentsSeparatedByCharactersInSet:[NSCharacterSet newlineCharacterSet]];

NSMutableArray *robots=[[[NSMutableArray alloc] init] autorelease];

NSMutableString *line= [[[NSMutableString alloc] init] autorelease];


for(line in parsed){
    range=[line rangeOfString:@"Disallow"];
    if (range.location != NSNotFound) {
        [line deleteCharactersInRange: NSMakeRange(1,9 )];
        [robots addObject:line];

    }
}   

and here is the error:

* Terminating app due to uncaught exception ‘NSInvalidArgumentException’, reason: ‘Attempt to mutate immutable
object with deleteCharactersInRange:’

Answer 1

The variable line in for(line in parsed) is immutable because an NSString is returned by the for-in statement construct.

Probably what you need:

for(NSString *line in parsed) {
    if [line hasPrefix:@"Disallow"]) {
        [robots addObject:[line substringFromIndex:9];
    }
}