On Tuesday, 2 June 2015 at 02:32:55 UTC, Andrei Alexandrescu
wrote:
On 6/1/15 7:18 PM, deadalnix wrote:
On Tuesday, 2 June 2015 at 00:11:09 UTC, Andrei Alexandrescu
wrote:
On 6/1/15 3:43 PM, deadalnix wrote:
On Monday, 1 June 2015 at 19:43:33 UTC, Andrei Alexandrescu
wrote:
Do not define constructors. They ostensibly imply
commitment to
remembering to call the appropriate destructor. A union can
only be
default constructed (with its init value as described) and
has no
destructor.
This is implied in C++ because of manual memory management.
I don't
think it is in D.
It is because destructors exist in both languages.
It is common in D to have a struct with a constructor and no
destructor.
Probably there's a misunderstanding then. I'm saying the right
way to go is unions have no destructors at all.
No, I asked you what is the rationale used to get types with
postblit/destructor in unions (right now, the spec says no). I
asked about the rationale for introduction of element with
destructor/copy constructor in C++, but it turns out that the
link provided also include constructor, and, in fact, only
explore the constructor case in the rationale.
It is important to consider why C++ did something to know if it
makes sense to import it in D. I remind you that this is a change
that you propose to the current state of affairs, meaning the
burden of proof in on you.
5/ union currently disallow members with postblit and/or
destructor
. It
seems that this was needed in C++ as per Andrei's
comments. It
seems to
me that, because of manual memory management, C++ would
have a lot
more
struct with copy constructor and/or destructor than in D,
so I'm not
sure if this require change in spec. Andrei, can you give
more details
on the C++ situation here ?
That rule has hurt C++ everywhere, and the community
credits Lois
Goldthwaite for pushing the current rule, which allows
types with
cdtors in unions. Let's go the same way, unions are all but
useless
otherwise.
Without knowing the rationale in C++, it is difficult to
assert that
this is also valid in D. You seems to be knowledgeable of
the subject,
so surely you can enlight us on that one.
I intentionally gave enough information to allow easy further
research. http://goo.gl/19Nol5 lists N2412 and N2248 as top
hits,
their motivation sections are relevant.
The abstract of the 2 above mentioned link only discuss the
*constructor* case. It was never question of struct with
constructor not
being able to be in union.
Then again sorry I am misunderstanding something. I'm saying
the right way to go is unions accept all types.
You are saying this. Many on that thread said otherwise. I
personally have no strong opinion one way or another. That is why
I'm asking about what makes you think element with
postblit/destructor needs to be accepted in unions, in order to
have all elements I needs to have an informed opinion.
Right now I'm not getting any of it, and instead I'm getting
confrontation. That is not productive.
You attitude is only weakening your point.
I'm not making a point. There is no debate. You said you want
to work on unions, that would be great. But this is a cut and
dried area. There's no room for creativity here. If you want to
be creative and design new programming language facilities, do
something else. For unions do what needs be done.
That is dishonest. First because there is almost no spec - so
there is much to debate, second because what you propose is
different from what is describe in the little spec there is
(literally, no postblit/destructor in the union or its elements
is the only that is specified).
Please stop projecting. You are the one being creative here.
