First Draft: Static Single Assignment

[Nick Treleaven]

On Wednesday, 3 December 2025 at 04:05:28 UTC, Peter C wrote:
> class Bag
> {
>     final int[] items; // This is a binding-level guarantee - 
> also acts an API invariant.
>     this() { items = []; }
> }
>
> void main()
> {
>     auto b = new Bag();
>     b.items ~= 1; // fine. still mutable.
>     b.items = []; // was expecting an error here??
> }

Just to note that final on a dynamic array `a` should mean that 
`a.ptr` and `a.length` never change, but elements e.g. `a[0]` can 
change. So if final was allowed on fields, both assignments above 
would error.