Fully transitive const is not necessary

[Christian Kamm]

>>  class C
>>  {
>>   mutable int x;
>>   void foo() const { x++; } // const but can't be pure
>>   void bar() pure
>>   { /* can't do anything in here you couldn't have done above */ }
>>  }

Janice Caron wrote:
> But you could equally well write it like this:
> 
>     class C
>     {
>         int x;
>         void foo() { x++; }
>         void bar() pure
>         { /* can't do anything in here you couldn't have done above */ }
>     }
> 
> If it can change, then don't call it const. Seems a simple enough rule to
> me.

Yes, but now const's transitivity isn't a necessity for 'future
multiprogramming features' anymore. Instead, we're discussing a const
scheme where mutable members could be allowed, but aren't - for simplicity,
consistency or some other reason.

I have not used D2 yet, so I'm not sure it is as restricting as some people
suggest. From the outside transitive const certainly looks simpler and more
useful than C++'s variant. However, if there are several genuine cases
where escapes from transitivity would be advantageous, allowing exceptions
should be considered.