Why does this NSMutableAttributedString addAttribute work only if I use a mutableCopy

Question

I have the following code :

NSMutableAttributedString *attrS = [[NSMutableAttributedString alloc] initWithString:@"• Get Tested Son"];
NSMutableAttributedString *boldS = [[NSMutableAttributedString alloc] initWithString:@"Son"];

[boldS addAttribute:NSFontAttributeName value:SOMEBOLDFONT range:NSMakeRange(0, boldS.length)];

[attrS replaceCharactersInRange:[attrS.string rangeOfString:boldS.string]
           withAttributedString:boldS];

As you can see, I want to bold the Son part. This does not work if I do the above statements but only works if I do :

[[attrS mutableCopy] replaceCharactersInRange:[attrS.string rangeOfString:boldS.string]
                         withAttributedString:boldS];

What might be the reason for that?

Answer 1

addAttribute works regardless of whether you take a mutableCopy. Your question is based on a false assumption. It therefore has no answer.

Run this:

NSMutableAttributedString *attrS = [[NSMutableAttributedString alloc] initWithString:@"• Get Tested Son"];
NSMutableAttributedString *boldS = [[NSMutableAttributedString alloc] initWithString:@"Son"];

UIFont *someBoldFont = [UIFont fontWithName:@"Arial" size:23.0f];
[boldS addAttribute:NSFontAttributeName value:someBoldFont range:NSMakeRange(0, boldS.length)];

NSMutableAttributedString *attrSCopy = [attrS mutableCopy];

[attrS replaceCharactersInRange:[attrS.string rangeOfString:boldS.string]
           withAttributedString:boldS];
[attrSCopy replaceCharactersInRange:[attrS.string rangeOfString:boldS.string]
           withAttributedString:boldS];

NSLog(@"%@", [attrS isEqual:attrSCopy] ? @"equal" : @"different");

It will output equal. Comment out the replaceCharactersInRange: for either attrS or attrSCopy and it will output different.