Rebooting the __metada/__mutable discussion

[Dennis]

On Wednesday, 13 April 2022 at 12:31:44 UTC, Zach Tollen wrote:
> Maybe there is some other natural use for `@system` variables. 
> But none of the use cases I have seen seem particularly 
> incompatible with the additional `__mutable` functionality.

Without conflating `@system` and `__mutable`:
```D
struct Boolean
{
     @system ubyte payload; // must be 0 or 1 or buffer overflows 
could happen
}

immutable Boolean b; // can be placed in read-only data segment
```

When conflating `@system` and `__mutable`, `b` suddenly must be 
placed in mutable memory.