Mutability is a great tool; it dramatically simplifies certain algorithms, and dramatically improves performance of others. But it comes at a cost, and there ar

Mutability is a great tool; it dramatically simplifies certain algorithms, and dramatically improves performance of others. But it comes at a cost, and there are situations in which it is inappropriate. So the language should force you to think before reaching for this tool. It shouldn't be the default tool for every problem.