D2: bug in struct postblit/dtor, or am I a burke?
daniel.keep.lists at gmail.com
Tue Mar 17 23:32:56 PDT 2009
I can't seem to get this to work properly. I'm trying to write a
copy-on-write proxy type. I'm using postblit and dtors along with the
usual ctors and opAssign to manage the refcount of the shared memory.
However, testing with dmd-2.026 (and a few previous versions a little
while ago), the attached program gives me the following output:
(NB: ">" means entering, "<" means leaving; these messages are printed
from in- and out-contracts. Printed values are the array being stored
and the ref count (or zero if the ref count pointer is null.))
> opAssign(T); COWArray(0x 0000[0..0]) @ 0
> ~this(); COWArray(0x 12FE88[0..4424652]) @ 1245120
< ~this(); COWArray(0x 12FE88[0..4424652]) @ 1245119
< opAssign(T); COWArray(0x AA2E40[0..4]) @ 1
> this(this); COWArray(0x AA2E40[0..4]) @ 1
< this(this); COWArray(0x AA2E40[0..4]) @ 2
> ~this(); COWArray(0x AA2E40[0..4]) @ 2
< ~this(); COWArray(0x AA2E40[0..4]) @ 1
For the following code:
a = [1,2,3,4];
// This shouldn't affect ref counts
auto a_str = a.toString;
writefln("a: %s", a_str);
As you can see, it correctly enters opAssign and leaves with the correct
array reference and ref count. However, it also spuriously calls the
destructor with what appears to be a random pointer. It then calls the
postblit when it shouldn't be doing so, resulting in the refcount being
one too high.
I've attached the full source (compile with -debug); does anyone know
what I'm doing wrong, or whether this is a compiler bug?
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