Very limited shared promotion

[aliak]

On Monday, 24 June 2019 at 13:20:23 UTC, Jonathan M Davis wrote:
> However, one issue with that from a usability perspective is 
> that even if you're doing all of the right stuff like 
> protecting access to the shared variable via a mutex and then 
> temporarily casting it to thread-local to operate on it while 
> the mutex is locked, if you want to actually assign anything to 
> the shared variable before releasing the mutex, you'd have to 
> use a pointer to it that had been cast to thread-local, whereas 
> right now, you're actually allowed to just assign to it. e.g.
>
> shared MyClass obj;
>
> synchronized(mutex)
> {
>     obj = cast(shared)someObj;
> }
>
> works right now, but if writing to shared variables were 
> illegal like it arguably should be, then you'd have to do 
> something ugly like
>
> shared MyClass obj;
>
> synchronized(mutex)
> {
>     auto ptr = cast(MyClass*)&obj;
>     *ptr = someObj;
> }

You can have the same usability/aesthetics:

synchronized {
   cast(MyClass)obj = someObj;
}

Doesn't that work?

Ideally though, I think you'd want:

class MyClass {
   void opAssign(MyClass c) shared { ... }
}