Helping with __mutable (which will be renamed to __metadata)

[Steven Schveighoffer]

On 4/15/19 9:14 AM, Radu wrote:

> I also have the impression that `shared` should be used here instead of 
> `__mutable`. Even in the current incarnation shared offers some limited 
> guarantees that atomicity is required for writing shared values. I think 
> people are working on making stronger guarantees for shared.
> 

Only immutable structs would have shared metadata. Normal mutable 
structs could have thread-local metadata. So that doesn't work.

-Steve