On Tuesday, 16 February 2016 at 08:04:32 UTC, Jonathan M Davis
wrote:
For that to work in D, we'd lose out on the guarantee that a
const object can't be mutated via a const reference to that
data - though with the current state of things, const does
become limiting enough that you can't use it under a number of
circumstances that you might like to (e.g. ref-counting), and
some folks mistakenly think that it's defined behavior to cast
away const and mutate and do it in their code.
Yes, casting away transitive const should be impossible.
The real issue is how to deal with calling overloaded C++
functions. Like, some C++ functions implements transitive const,
others do head const combined with mutable. So it is insufficient
to look at the C++ sigature... Which means D ought to have some
stronger way to specifing constness for C++ signatures than C++
provides.
But even if we went that route, that's still a whole other
ballgame from non-transitive const. There are some major
implications for const if we making it legal to cast it away
and mutate as long as the underlying data is mutable rather
than immutable, but from a language complexity standpoint, it's
not particularly problematic, whereas non-transitive const is.
Yes, please don't allow casting from const to mutable, D should
aim for stronger typing and better optimization.
