shared - i need it to be useful

[Nicholas Wilson]

On Wednesday, 17 October 2018 at 07:24:13 UTC, Stanislav Blinov 
wrote:
> On Wednesday, 17 October 2018 at 05:40:41 UTC, Walter Bright 
> wrote:
>
>> When Andrei and I came up with the rules for:
>>
>>    mutable
>>    const
>>    shared
>>    const shared
>>    immutable
>>
>> and which can be implicitly converted to what, so far nobody 
>> has found a fault in those rules...
>
> Here's one: shared -> const shared shouldn't be allowed. 
> Mutable aliasing in single-threaded code is bad enough as it is.

Could you explain that a bit more? I don't understand it, mutable 
-> const is half the reason const exists.

I was thinking that mutable -> shared const as apposed to mutable 
-> shared would get around the issues that Timon posted.