shared - i need it to be useful

[Stanislav Blinov]

On Thursday, 18 October 2018 at 19:51:17 UTC, Erik van Velzen 
wrote:
> On Thursday, 18 October 2018 at 19:26:39 UTC, Stanislav Blinov

>>> Manu said clearly that the receiving thread won't be able to 
>>> read or write the pointer.
>>
>> Yes it will, by casting `shared` away. *Just like* his 
>> proposed "wrap everything into" struct will. There's exactly 
>> no difference.
>>

> Casting is inherently unsafe. Or at least, there's no 
> threadsafe guarantee.

So? That's the only way to implement required low-level access, 
especially if we imagine that the part of Manu's proposal about 
disabling reads and writes on `shared` values is a given. It's 
the only way to implement Manu's Atomic!int, or at least 
operation it requires, for example.

>>> You can still disagree on the merits, but so far it has been 
>>> demonstrated as a sound idea.
>>
>> No, it hasn't been.
>
> I think you are missing the wider point. I can write 
> thread-unsafe code *right now*, no casts required. Just put 
> shared at the declaration. The proposal would actually give 
> some guarantees.

No, I think you are missing the wider point. You can write 
thread-unsafe code regardless of using `shared`, and regardless 
of it's implementation details. Allowing *implicit automatic 
promotion* of *mutable thread-local* data to shared will allow 
you to write even more thread-unsafe code, not less.

The solid part of the proposal is about disabling reads and 
writes. The rest is pure convention: write structs instead of 
functions, and somehow (???) benefit from a totally unsafe 
implicit cast.