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Comment by jonhohle | Hacker News Reader

    > This is an idea I got that isn't really implemented
    > in any language I know of.

Is this different than an arg declared as a const reference in C++. Or since fields are still mutable, like `final` arguments in Java?

I think yes, it's like declaring every single argument as const.

Algol68 had this property. Consider

  STRUCT (INT x, y) z = (1, 2)

Here z is a const struct. If you wanted a variable, you'd have to say

  STRUCT (INT x, y) z;
  z := (1, 2)

or equivalently

  REF STRUCT (INT x, y) z = LOC STRUCT (INT x, y) := (1, 2)

Basically a variable has a REF mode.