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

[Andrei Alexandrescu via Digitalmars-d]

On 07/02/2017 02:49 AM, Shachar Shemesh wrote:
> On 02/07/17 02:08, Andrei Alexandrescu wrote:
>> Vaguely related question: should "const" convert implicitly to "const 
>> shared"? The intuition is that the latter offers even less guarantees 
>> than the former so it's the more general type. See 
>> http://erdani.com/conversions3.svg.
> 
> I don't see how it can. They provide different guarantees. If anything, 
> it should be the other way around.
> 
> If you hold a pointer to const, you know the data will not change during 
> the function's execution. No such guarantees for const shared.

That supports the case for allowing the conversion.

const: "You have a view to data that this thread may or may not change."

const shared: "You have a view to data that any thread may or may not 
change."

So the set of const is included in the set of const shared - texbook 
inclusion polymorphism.


Andrei