what to do with postblit on the heap?

[Steven Schveighoffer]

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