On Wed, Aug 28, 2013 at 02:13:39AM +0200, deadalnix wrote:
> On Tuesday, 27 August 2013 at 16:57:36 UTC, H. S. Teoh wrote:
[...]
> >Also, the fact that move() uses memcpy is a bit worrying; Adam Ruppe
> >& myself ran into a nasty bug involving closures over struct members
> >when the struct may get moved upon return from a function. For
> >example:
> >
> > struct S {
> > int id;
> > void delegate()[] cleanups;
> >
> > this() {
> > id = acquireResource();
> > cleanups ~= {
> > // N.B.: closure over this.id
> > releaseResource(id);
> > };
> > }
> > }
> >
> > S makeS() {
> > // Problem: S.cleanups[0] is a closure over the struct
> > // instance on this function's stack, but once S is
> > // returned, it gets memcpy'd into the caller's stack
> > // frame. This invalidates the delegate's context
> > // pointer.
> > return S(1);
> > }
> >
> > void main() {
> > auto s = makeS();
> > // Problem: s.cleanups[0] now has an invalid context
> > // pointer. If the stack is reused after this point, the
> > // dtor of s will get a garbage value for s.id.
> > }
> >
> >Using move() to move a resource from a local variable into a member
> >looks like it might be vulnerable to this bug as well -- if the
> >resource has closures over member variables it might trigger this
> >problem.
> >
> >
> >T
>
> Funny, I ran into this twice this week XD
>
> struct are movable by definition, so the compiler should reject this
> unless the delegate is scope.
Is scope even implemented right now? :-/ It's one of those things that
are really, really nice to have, but so far haven't materialized yet.
T
--
Guns don't kill people. Bullets do.
