On Mon, Sep 23, 2013 at 07:29:39PM -0400, Nick Sabalausky wrote:
> On Mon, 23 Sep 2013 17:02:09 +0200
> "Adam D. Ruppe" <destructiona...@gmail.com> wrote:
>
> > We should really deprecate the new keyword. It'd break like all
> > code ever, but with D's templates, there's no need for it, and
> > when it is there, it is going to spark problems about replacing
> > global allocators or the library allocators being second class
> > citizens.
> >
>
> I think that's addressing the wrong problem, it wouldn't solve much,
> if anything. We'd just end up with a lot of lib writers (and others)
> hardcoding in usage of the default allocator. So it'd be exactly the
> same as now, just with uglier syntax and a ton of breakage.
>
> What's ultimately needed is a way to change the default allocator for
> not only "new" but also array concatenation, closures, and any other
> part of the language that might allocate. That way, we actually *do* get
> the benefits we're looking for, plus we keep the nicer current syntax
> and no breakage.
>
> tl;dr: "new" is a red herring. The real issue is being able to easily
> replace the default allocator.
I thought Walter's DIP already addresses the issue of replacing the
default allocator?
http://wiki.dlang.org/DIP46
I get the feeling that we don't have a good handle on the fundamental
issues, though. Having a stack for managing the default allocator works
for the simpler cases, but it's unclear how things would interact once
you throw in other requirements, like class/struct-scoped allocators,
block scoped allocators inside closures, user-specified allocators that
must interact with the foregoing, etc..
For example, it's relatively easy to understand this:
void doWork() {
gc_push(MyAlloc);
scope(exit) gc_pop();
... // do work
}
void doMoreWork() {
gc_push(AnotherAlloc);
scope(exit) gc_pop();
... // do work
}
void main() {
doWork();
doMoreWork();
}
But once you throw in closures and delegates, things become rather murky:
auto getCallback() {
gc_push(MyAlloc);
scope(exit) gc_pop();
int closed_var;
return {
// What does this do?
closed_var++;
string x = "abc";
x ~= "def"; // which allocator does this use?
};
}
void main() {
auto dg = getCallback();
gc_push(OtherAlloc);
scope(exit) gc_pop();
dg(); // Hmm...
}
T
--
May you live all the days of your life. -- Jonathan Swift
