shared - i need it to be useful

[Kagamin]

On Monday, 15 October 2018 at 18:46:45 UTC, Manu wrote:
> Current situation where you can arbitrarily access shared 
> members
> undermines any value it has.

The value of shared is existence of thread-local data that's 
guaranteed to be not shared, so you don't need to worry about 
thread-local data being shared, and shared protects that value 
well.

> Assuming this world... how do you use shared?

Unique solution for each case.

> If you write a lock-free queue for instance, and all the 
> methods are
> `shared` (ie, threadsafe), then under the current rules, you 
> can't
> interact with the object when it's not shared, and that's fairly
> useless.

Create it as shared.

> Assuming the rules above: "can't read or write to members", and 
> the understanding that `shared` methods are expected to have 
> threadsafe implementations (because that's the whole point), 
> what are the risks from allowing T* -> shared(T)* conversion?

All data becomes possibly shared, so you can't assume it's 
unshared, effectively C-style sharing. BTW D supports the latter 
already.