I have submitted a fix for bug 5272,
http://d.puremagic.com/issues/show_bug.cgi?id=5272 "Postblit not called on
copying due to array append"
However, I am starting to realize that one of the major reasons for
postblit is to match it with an equivalent dtor.
This works well when the struct is on the stack -- the posblit for
instance increments a reference counter, then the dtor decrements the ref
counter.
But when the data is on the heap, the destructor is *not* called. So what
happens to any ref-counted data that is on the heap? It's never
decremented. Currently though, it might still work, because postblit
isn't called when the data is on the heap! So no increment, no decrement.
I think this is an artificial "success". However, if the pull request I
initiated is accepted, then postblit *will* be called on heap allocation,
for instance if you append data. This will further highlight the fact
that the destructor is not being called.
So is it worth adding calls to postblit, knowing that the complement
destructor is not going to be called? I can see in some cases where it
would be expected, and I can see other cases where it will be difficult to
deal with. IMO, the difficult cases are already broken anyways, but it
just seems like they are not.
The other part of this puzzle that is missing is array assignment, for
example a[] = b[] does not call postblits. I cannot fix this because
_d_arraycopy does not give me the typeinfo.
Anyone else have any thoughts? I'm mixed as to whether this patch should
be accepted without more comprehensive GC/compiler reform. I feel its a
step in the right direction, but that it will upset the balance in a few
places (particularly ref-counting).
-Steve
- what to do with postblit on the heap? Steven Schveighoffer
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