shared - i need it to be useful

[Timon Gehr]

On 17.10.2018 15:40, Steven Schveighoffer wrote:
> On 10/17/18 8:02 AM, Timon Gehr wrote:
>> Now, if a class has only shared members, that is another story. In 
>> this case, all references should implicitly convert to shared. There's 
>> a DIP I meant to write about this. (For all qualifiers, not just shared).
> 
> When you say "shared members", you mean all the data is shared too or 
> just the methods are shared?
> 
> If not the data, D has a problem with encapsulation. Not only all the 
> methods on the class must be shared, but ALL code in the entire module 
> must be marked as using a shared class instance. Otherwise, other 
> functions could modify the private data without using the proper synch 
> mechanisms.
> 
> We are better off requiring the cast, or enforcing that one must use a 
> shared object to begin with.
> 
> I think any sometimes-shared object is in any case going to benefit from 
> parallel implementations for when the thing is unshared.
> 
> -Steve

The specific proposal was that, for example, if a class is defined like 
this:

shared class C{
     // ...
}

then shared(C) and C are implicitly convertible to each other. The 
change is not fully backwards-compatible, because right now, this 
annotation just makes all members (data and methods) shared, but child 
classes may introduce unshared members.