On Tuesday, 16 October 2012 at 17:17:36 UTC, Jonathan M Davis
wrote:
On Tuesday, October 16, 2012 06:40:54 H. S. Teoh wrote:
Notice in the second output range, that the third element is
[20, 203]
instead of [100, 203], and thereafter a bunch of elements are
skipped,
and things just start going haywire after that.
The only difference between the two is that the first is
computed within
main(), and the second is returned from a function call. Does
this mean
that it's unsafe to return composed ranges from functions?
No. I don't know what's going on, but it sounds like there's a
bug somewhere.
I'm trying to
think what might be going wrong. Could it be that the composed
ranges
are stack-allocated temporaries that go out of scope upon
returning from
the function, so the returned range is actually accessing
invalid
memory? (That is a really scary thought.)
If you have a range over static array, then yes, you will have
serious issues
if you return a range over it, because the data is going away,
but that's not
going to happen with a struct or class. The class would be
safely on the heap,
and the struct will get appropriately copied. But one area that
could get
hairy if dmd is buggy is if you're using delegates which access
the stack
frame. It's supposed to work just fine, but it requires that a
closure be
allocated so that the state of the stack frame is saved (and is
therefore
valid after the function call has completed). So, things could
definitely go
funny if there are any bugs in there.
I have no idea what's going wrong for you here (I'd have to
spend time
studying exactly what your code is doing), but there's either a
bug in your
code or a compiler bug which is causing you problems, because
aside from
slices of static arrays, it's perfectly safe to return
stack-allocated stuff
functions - including several layers of ranges.
- Jonathan M Davis
No idea either, but I'll volunteer to investigate ;)
I agree with Jonathan though, sounds like a bug somewhere. There
is no reason for your code to fail.
I'll post back if I find anything.
