On Sunday, 15 November 2015 at 14:54:51 UTC, Andrei Alexandrescu
wrote:
On 11/15/2015 09:34 AM, Dicebot wrote:
On Sunday, 15 November 2015 at 14:23:05 UTC, Jonathan M Davis
wrote:
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 ...
Casting away _const_ is already legal if programmer can himself
guarantee underlying object has mutable origin (i.e. not
available via
immutable reference), by the very definition of const. It is
casting
away immutable and mutating that is strictly UB.
Correct. I'm not sure whether that's clarified in the language
documentation yet. -- Andrei
Quite the opposite in fact. Walter recently approved an update to
the spec which clarified that it _is_ undefined behavior to cast
away const and mutate even if the object being referred to isn't
immutable underneath the hood:
https://github.com/D-Programming-Language/dlang.org/pull/1047
And from what I've seen, Walter has always been adamant that D's
const is physical const and that casting away const and mutating
is undefined behavior, arguing that if it weren't, it would be
like C++'s const and that C++'s const is pretty much useless,
because it doesn't provide actual guarantees. So, if he's now
willing to have casting away const and mutating be well-defined
behavior, that's a big shift.
- Jonathan M Davis
