On Saturday, 26 May 2012 at 11:35:29 UTC, Jacob Carlborg wrote:
On 2012-05-25 14:05, foobar wrote:
If you have a pointer to a struct you don't know how it was
created.
It's possible it's been created with "new", which means the
garbage
collector needs to delete it.
let's say we add two classes:
class FooA {
A a;
}
class FooPA {
A* pa;
}
For the first case, both the class and the struct share the
same
lifetime thus when an instance of FooA is GC-ed, the GC would
call A's
d-tor and allow it to do what-ever (self) cleaning it
requires. This
means the d-tor will always be called.
Is that the cases even if the destructor of FooA isn't called?
Huh? In my model FooA has no destructor.
For the second case, The GC will only scan "pa" to find inner
class
instances but will *not* handle the struct value itself.
In order to clean what "pa" points to, you need to explicitly
call the
destructor yourself.
Are you saying that the GC won't collect a struct allocated
with "new"?
http://dlang.org/expression.html#NewExpression
"NewExpressions are used to allocate memory on the garbage
collected heap...". I though that everything allocated via the
GC was also collected by the GC.
I indeed propose that structs allocated with "new" will be put in
region of the heap *not* managed by the GC. It's a tiny price to
pay to get more orthogonal semantics which are easier to reason
about.
Please note that this only affects code that directly uses
pointers which is not common in D and is geared towards more
advanced use cases where the programmer will likely want to
manage the memory explicitly anyway.
One way to do this would be to register a callback
with the GC to get notified when an instance of FooPA is
collected and
inside the callback function maintain a reference-counter.
This also means that if you allocate a struct value on the
heap via
"new" you are responsible to call delete _yourself_ and the gc
will not
call it for you.
I think that loosing this small convenience is worth it - we
gay more
orthogonal semantics that are easier to reason about.
