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.
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.
7/ struct with anonymous union in them have one entry per union field in
their tupleof. All the union field should be present as one entry in the
tupleof, with a compiler generated union type.
Again the litmus test here is enabling introspection. Structs with
anonymous union members should have one member called e.g.
__anonymous__ in their tupleof, and in turn introspecting that member
should list its tuple.
Compiler generated tuples are auto flattening in D. That would not work
unless the entry in the struct tuple is an (compiler generated) union.
So it seems like generating an __anonymous__ name is the way to go.
Andrei
