Immutability is one aspect of the family of techniques called "functional". Yes, you can right immutable code in C or Java, but the compiler can't verify that i

Immutability is one aspect of the family of techniques called "functional". Yes, you can right immutable code in C or Java, but the compiler can't verify that intent in general, which means that a whole class of bugs are possible, and certain kinds of high-level general functions (combinators) and automatic optimizations (inlining and rewrites and skipping computations) are not possible to write/apply.