7.2. Mutability

Most of the base Foundation value classes come in two flavors: mutable and immutable. The word “mutable” means that the value of the object can be changed. You can’t change the contents of an NSString once you create it, but you can change the contents of an NSMutableString:

NSMutableString* name = [NSMutableString stringWithString:@"Helen"];
[name setString:@"Sarah"];
[name setString:@"Daisy"];