`restricted` member variables

[Paul Backus]

On Monday, 20 June 2022 at 11:04:16 UTC, Mike Parker wrote:
> From that perspective, I see massive gaping hole here. I've 
> done a complete 180 on need for further restricting member 
> variable access. But I'm seeing it more granularly than 
> class-level and down to the function level.
>
> After some spitballing, here's something I like:
>
> ```d
> class E
> {
>    restricted int _y;
>    restricted(_y) void y(int newY) { _y = newY; }
> }
> ```

This is very similar in concept to `@system` variables, except 
instead of a single `@system`/`@trusted` attribute pair, you have 
individual `@trusted`-like attributes for each specific variable.

For comparison:

```d
class E
{
     @system int _y;
     @trusted void y(int newY) { _y = newY; }
}
```

I'm not convinced the extra granularity is worth adding an entire 
new attribute for.