On Sat, 10 Jul 2010 01:06:39 -0400, Jonathan M Davis
<jmdavisp...@gmail.com> wrote:
I thought that classes always went on the heap and that structs always
went on
the stack - so allocating structs with new wouldn't work. Also, I
thought that
delete was deprecated if not outright removed from D. And yet, we have a
new bug
that Andrei reported about destructors for structs not working correctly
when
they're allocated with new (and delete is being used to destroy it in
the code
in the report).
http://d.puremagic.com/issues/show_bug.cgi?id=4442
Code from bug report:
struct S1{ ~this() { writeln("dtor"); } }
void main() {
auto a = S1();
auto b = new S1();
delete b;
auto c = new S1();
c = null;
GC.collect();
}
Am I missing something here? TDPL was quite clear that classes were
reference
types and structs were value types, and here we appear to have a struct
used as
a reference type. Is this some sort of feature from outside of SafeD, or
is it a
feature that was supposed to be removed but hasn't yet, or what? I know
that
TDPL doesn't cover everything and that what dmd does doesn't always
match it
yet, but from what I understood from reading TDPL, the code above
shouldn't
compile at all since it's using a struct like a class and is using the
supposedy
defunct delete operator.
- Jonathan M Davis
A new statement can also allocate value types on the heap and return a
pointer to them. For example, the type of b and c is S1* and the GC
doesn't know about C's destructor. Please refer to the D spec on new
(http://www.digitalmars.com/d/2.0/expression.html#NewExpression) or TDPL
page 51. Both state that any type can be used with new; no limitations
with regard to reference or non-reference types are mentioned. Also, on
page 269 of TDPL there is an example of containing a Node*.
As for the bug, it's actually somewhat old. Issue 2834 was filed back in
April of 09 - Struct Destructors are not called by the GC, but called on
explicit delete. And this is a bug in the spec, not DMD; the only way to
run struct destructors from the GC is to add vtables to them or hidden in
the GC (i.e. to make them classes). By the way, structs inside of classes
do get their destructors called.
As for delete and clear, the deprecation/transition is still in progress.
clear exists, but delete is not deprecated yet.
