Immutability gives guarantees at runtime, a type system gives guarantees at compile time. Or, from a different perspective, immutability guarantees a certain pr

Immutability gives guarantees at runtime, a type system gives guarantees at compile time. Or, from a different perspective, immutability guarantees a certain property – the value – of an item, while a type system guarantees different properties for all items of a type. Those two concerns are mostly orthogonal to each other.