On Saturday, 13 December 2014 at 21:20:43 UTC, Andrey Derzhavin
wrote:
import std.stdio;
class ObjectAType {
bool ok;
this() {ok = true;}
}
void main()
{
auto a = new ObjectAType;
assert(a.ok);
destroy(a);
assert(!a.ok); // a has been destroyed.
}
This method of detection of collected objects is what I needed.
Thanks to everybody for your advise.
Be careful - the memory could still have been reused. For example:
assert(a.ok);
destroy(a);
// ... lots of code, maybe multi-threaded ...
assert(!a.ok); // can fail
If between `destroy()` and the second `assert()`, the memory of
the object is collected, a new object (of the same or different
type) can have been placed there. You will then read an arbitrary
piece of data from that new object, which may or may not evaluate
to `true`.
The only case where this can be safe is when you can guarantee
that there are no new memory allocations between the destruction
and the test, or that the GC doesn't run. The first condition may
also be no longer sufficient if the GC starts moving objects
around (the current one doesn't).
Really, in practice you just cannot safely access GC managed
resources from inside a GC destructor. You're just asking for
trouble if you try to hack around that fact.
