Inherited const when you need to mutate

[Andrei Alexandrescu]

On 7/10/12 7:57 PM, Walter Bright wrote:
> On 7/10/2012 4:16 PM, Timon Gehr wrote:
>> Const is stronger than what is required to bridge the gap between
>> mutable and immutable. It guarantees that a reference cannot be used to
>> mutate the receiver regardless of whether or not the receiver is
>> immutable underneath. That is unnecessary as far as immutable is
>> concerned. It only needs to guarantee that the receiver does not change
>> if it is immutable underneath.
>
> If you have a const function that accepts both mutable and immutable
> args, then that function *by definition* cannot tell if it received
> mutable or immutable args.

It can if immutable(T) is invalid.

> Furthermore, a const function is saying it will not change, even if
> mutable data is passed to it.

Lazy computation does not produce detectable change.

> Everything falls apart once you allow "logical const" in. You'll be in
> the same boat as C++ const, which is faith-based programming rather than
> checkable programming.

Then please do not suggest pimpl and casting. That is UNDEFINED. If you 
want to ascribe any meaning to it, you ruin all the work we've done on 
immutability.


Andrei