[Gretl-devel] Re: subtle list in bundle in function problem
Am 16.06.2024 um 18:37 schrieb Allin Cottrell:
On Sun, 16 Jun 2024, Sven Schreiber wrote:
...
> Yep, I basically know all that. I'm also not exactly sure what I'd
> prefer in this case. But the point is that when leaving the function,
> the list inside the bundle becomes invalid, but nobody tells the user
> about this situation. Instead, you get type changes and other side
> effects that are only expected when you really know the internals of
> gretl. So perhaps what I'm trying to say is that some warning or
> error might be useful.
"Doctor, it hurts when I do this." "Well then, don't do that."
Hehe -- well, it all started because gretl has a one-element 'ylist' in
its model bundle which I needed/wanted to imitate, not because I had
this crazy idea in the first place...
I agree this is kinda complicated, but I think you're making it more
complicated than it need be. A function writer who has read the
chapter of the User's Guide on User-defined functions should know that
if you return in a bundle a list that references series that are local
to the function it will be little or no use to the caller: so don't do
it. It's not really a matter of hidden "internals" but of documented
behaviour -- but of course if the documentation isn't as clear as it
should be, that ought to be rectified.
I just checked the chapter on user-defined functions and I cannot find
that explanation. I presume that you are talking of the paragraph
"Series and lists as bundle members" in the previous chapter on "Gretl
data types", where functions aren't mentioned (and rightly so, at that
point in the guide).
BTW, in that function-related chapter in the "Return values" section it
says: "Having a function return a list or bundle is a way of permitting
the “return” of more than one variable." Maybe the possibility of arrays
could also be mentioned there.
thanks
sven