Why only string is immutable & not other data types

Question

I always wonder when it comes to mutability. Why .net designers have developed only stringbuilder class to achieve mutability of string class & not intbuilder for int considering int & string are implemented exactly the same way irrespective of their data types.

Answer 1

Many other languages provide similar design for strings: Java with StringBuffer and StringBuilder, Scala with StringBuilder, Python with MutableString though there are other, beter solutions in Python. In C++ strings are mutable, so no need for a builder.

The reason why builder exist for strings is:

1. Many languages define string as immutable (any change requires a new object in memory)
2. Strings tend to be large, much larger than ints
3. [1] and [2] combined cause inefficiency

The reason why builder doesn't exist for int:

1. It is simple data structure by itself
2. Most CPU have optimised instructions to deal with simple numbers (add, take away, etc)
3. Most CPU would efficiently process [2] instructions in just one or a few cycles, using registers or fast CPU cache
4. [2] and [3] combined remove the need for optimisation
5. There is little need to mutate an int per se, however, if you need to, you can use BitConverter or binary shift operations