(DMD) problem with closures/delegate literals and structs?

[Johannes Pfau]

Am Sat, 7 Dec 2013 08:43:53 -0800
schrieb "H. S. Teoh" <hsteoh at quickfur.ath.cx>:

> On Sat, Dec 07, 2013 at 10:08:25AM +0100, Johannes Pfau wrote:
> [...]
> > It looks like we actually generate a closure here which contains the
> > this pointer instead of directly using the struct as a context
> > pointer.  That is probably an optimization bug in dmd, but it
> > doesn't matter in this case as the problem would exist for closures
> > and normal delegates.
> 
> The problem is that delegates are never passed the this pointer from
> the caller; it is assumed that it's part of their context. You never
> write `myStruct.dg(args)`, but simply `dg(args)`. But by the time the
> delegate is invoked, you can't guarantee that `this` is still valid.
> Only the caller knows what copy of the struct it still holds, but
> this isn't communicated to the delegate. (On second thought, even if
> it *did* pass the updated `this` to the delegate, it would still be
> wrong, because there could be multiple copies of the struct by then,
> and who knows which copy the delegate was supposed to be operating
> on?)

True, but that's not what I meant ;-)
I always get the terminology related to closures wrong so sorry if that
didn't make sense.

What I meant is this: In the first example I posted,
http://dpaste.dzfl.pl/433c0a3d
the delegate does not access _function variables_. It only accesses the
this pointer. So there's no need for it to be a real closure and
allocate memory, it could instead be a normal delegate with the context
pointer simply set to the this pointer at the moment the delegate is
created.