Why do "const inout" and "const inout shared" exist?

[Timon Gehr via Digitalmars-d]

On 02.07.2017 15:48, Andrei Alexandrescu wrote:
> On 07/02/2017 09:39 AM, Timon Gehr wrote:
>> In general, depending on the hardware memory model and the language 
>> memory model, data transfer from one thread to another requires 
>> cooperation from both parties. We don't want the thread that has the 
>> unshared data to need to participate in such a cooperation.
> 
> Yes, there must be a handshake. Oh, I see your point. Let me illustrate:
> 
> void fun(const shared int* p1)
> {
>     auto a = atomicLoad(p1);
>     ...
> }
> 
> void gun()
> {
>      int* p = new int;
>      shared const int* p1 = p; // assume this passes
>      spawn(&fun, p);
>      *p = 42; // should be a shared write, it's not
> }
> 
> Is this what you're referring to?
> ...

Yes, precisely.

> So it seems like the hierarchy in http://erdani.com/conversions.svg is 
> minimal?
> 

Yes, I think there is no way to collapse it without bad consequences.