On 5/22/18 12:57 AM, Manu wrote:
On 21 May 2018 at 15:39, Steven Schveighoffer via Digitalmars-d
<digitalmars-d@puremagic.com> wrote:
On 5/21/18 6:26 PM, Manu wrote:
On 21 May 2018 at 14:53, Jonathan M Davis via Digitalmars-d
<digitalmars-d@puremagic.com> wrote:
On Monday, May 21, 2018 14:33:44 Manu via Digitalmars-d wrote:
How do virtual destructors work in normal D classes?
It is my understanding that destructors in D are never virtual but rather
that the runtime handles calling them correctly.
Can someone please elaborate on this?
I want to know exactly what this means in practise.
What he means by never virtual is *ALWAYS* virtual ;) At least in the sense
of virtual C++ destructors, not ordinary virtual functions.
Here is what the runtime does:
https://github.com/dlang/druntime/blob/38d784a8acd9cfe6ff4dadac6883a40f392f7353/src/rt/lifetime.d#L1380
In essence, each classinfo has it's "local" destructor,
Oooooohhh! It's in the classinfo (and not in the vtable!).
I knew that actually, I have run into that code, I just forgot!
It's in the classinfo, but so is the vtable. It's not really any
different, except the "slot" for the destructor is not in the vtable
array, it's just a separate member. See here:
https://github.com/dlang/druntime/blob/38d784a8acd9cfe6ff4dadac6883a40f392f7353/src/object.d#L957
Okay, so it's not directly in the vtable, it's special-case... (it's
actually an additional indirection over C++ to reach the dtor)
Not sure how C++ works. I think it's an extra indirection for any
virtual function in D, since D only stores the classinfo pointer. In
fact, the destructor is one less indirection, because it's not in an array.
Proper extern(C++) handling will need to take that same function and
jam it in the first slot of the C++ vtable instead, but it should be
functionally identical I think.
I don't know if that's true. The destructor itself does NOT call the
base class destructor automatically. That's why the machinery in
lifetime.d exists. It's actually, come to think about it, a LOT of
indirections (2 per class in the hierarchy).
It all depends on how C++ implements virtual destructors.
...Rereading...
Oh wait, you mean jam the *lifetime* function in the slot? Yeah, that
would probably work.
-Steve
