Second draft: Sum Type by Struct

[Per Nordlöw]

On Thursday, 10 September 2026 at 16:54:51 UTC, Per Nordlöw wrote:
> On Thursday, 3 September 2026 at 11:45:12 UTC, Richard (Rikki) 
> Andrew Cattermole wrote:
>> This is the second iteration of sumtype by struct proposal.
>
> Can we please reserve the support for sub-byte packing of `N` 
> tag bits for the sake of compacter memory layouts such as 
> polymorphic pointers being only of `2^^N` different types?

I also have written and used a radix-trie that uses the same 
bit-packing of the tag to store a tree value in place and a 
pointer to a sub-tree in the same word (`size_t`).