> They're not. The semantics of value types and reference types are different in the presence of mutation. I think C#'s overloaded term for "value-types" may h

> They're not. The semantics of value types and reference types are different in the presence of mutation. I think C#'s overloaded term for "value-types" may have caused you to misinterpret the above. Let me be more clear, if a value lives on the stack or the heap is completely separable from if it is mutable or not, that's my objection. > ... just as well by modifying and replacing an immutable value in a mutable cell In terms of "correctness", sure. In terms of performance see my 300+ float block example above. I shouldn't have to copy, modify, copy when I can just mutate in-place(and be explicit about that rather than relying on language semantics). Also I can seem to find any mention in the docs about Ref's semantics aside from a passing mention in the FFI section.