Fully transitive const is not necessary

[Steven Schveighoffer]

"Janice Caron" wrote
> On 03/04/2008, Steven Schveighoffer wrote:
>>  > Can you give me a counterexample of a logically const (muty) class in
>>  > which the non-mutable subset is actually useful?
>>
>> Certainly:
>> <snip>
>
> In the example you just gave me, the non-mutable subset consisted of
> the empty set - i.e. no members whatsoever. I don't call that useful.
>
> Given that, the function pure f could just have easily have been taken
> outside the class altogether and been a standalone function.
>
> Do you want to try again?

Have you no imagination? :)

class SuperIntensiveCalculator
{
    private mutable int[int] cache;

    private int configParameterThatIsNecessaryForIntenseCalculation;

    int f(int x) const
    {
         int *result = x in cache;
         if(result !is null)
             return result;
         /* do really intense calculation, cache the value */
    }

    pure int puref(int x) invariant
    {
        /* do really intense calculation, do not use cache */
    }
}