On Sunday, 15 November 2015 at 12:56:27 UTC, Andrei Alexandrescu
wrote:
On 11/14/2015 05:49 PM, Timon Gehr wrote:
List uses RC internally. I don't think the UB casts will stay
for the
final version, unless you are willing to completely dilute the
meaning
of const in ways that Walter has explicitly expressed will not
be done
in the past.
As I mentioned, he's okay with changing the language to make
the casts well defined. -- Andrei
Well, that's a big change, since it pretty much means that D's
const isn't physical const anymore, and Walter has been _very_
insistent about that in the past - to the point that he's argued
that C++'s const is outright useless because it isn't physical
const. If casting away const and mutating is well-defined
behavior, then we basically have C++'s const except that it's
transitive, and you have to be careful to make sure that the
object isn't actually immutable underneath the hood instead of
mutable, whereas C++ doesn't have immutable.
But if we go that route, personally, I think that it would be far
better to do something like @mutable and leave mutating const and
undefined outside of @mutable, particularly since if we can
implement @mutable properly, then the compiler can guarantee that
the object being mutated isn't actually immutable, and it avoids
the need for casting altogether, which reduces the risk of bugs
even when immutable isn't involved. It also means that the
programmer can determine whether an object is really only
logically const rather than physically const by looking at its
member variables rather than having to dig through all of its
code to see whether it ever casts away const.
- Jonathan M Davis
