NSMutableString s; ... -(void)functionA:(NSString )string { [self.s appendString: string]; }

-(void)functionB:(NSString )string { NSString c = self.s; NSString* c = [NSString stringWithString: self.s]; }

"Returns a string created by copying the characters from another given string."

self.s is a refernce to s, might change over time, stringWithString makes a copy, a "snapshot" of self.s...