PPA for OpenSCAD 2021
The only mutable variables in OpenSCAD are the C style loop variables, so
if you want to iterate over an array and accumulate the result you can't do
it with the classic OpenSCAD loop. You can do it with the C style loop but
making operations on undef a warning has pretty much broken that as you
have to add an ugly guard condition that is pointless. There is no problem
with the final value becoming undefined because it is never used. I only
want to be told a value is undef when I try and use it for something that
needs a definite value, such as cube().
I agree recursion is much cleaner.
On Sun, 25 Apr 2021 at 18:45, adrianv avm4@cornell.edu wrote:
Are you saying that has something to do with iterating over all the
elements in an array?
The problem with the orphan iteration in for loops is almost always a
problem that requires some special handling, whether or not undef is silent
in arithmetic. The problem is the stupid behavior of c-style for, not
undefs. And in my experience the code is harder to read for c-style for
than for recursion. I think the quoted example, a vector sum code, is
harder to read than a basic recursive version. And also, vector sum can be
done non-recursively by vector multiplication: b * [for(x=b) 1]
nophead wrote
You need to use the C style loop to be able to accumulate j in the loop.
Or
use recursion.
On Sun, 25 Apr 2021 at 18:10, adrianv <[hidden email]
http:///user/SendEmail.jtp?type=email&email=avm4%40> wrote:
I did some timing tests with C-like for vs recursion and found that
actually C-like for was slower. I don't know how broadly applicable
those
test results were, but it seems like in many cases (most cases?) it's
better to just use recursion.
I do not understand how undef in arithmetic makes it "slightly harder to
iterate over all values in an array". I don't even see any connection
between these things. To iterate over all values in an array you do
for(entry=array) ....
Ronaldo wrote
That is a well-known design issue of the C-like for. The last iteration
is
useless. See: https://github.com/openscad/openscad/issues/3227
The only way I know to handle the issue is to protect the expressions in
the loop avoiding illegal operations in the last iteration.
b= [1,2,3];
a = [for (i=-1, j=0; i<len(b); i=i+1, j= (i==len(b)) ? j : j+b[i]) j];
echo(a);
Em dom., 25 de abr. de 2021 às 12:50, julianstirling <
[hidden email] <
http:///user/SendEmail.jtp?type=email&email=julian%40.co>
http:///user/SendEmail.jtp?type=email&email=julian%40.co%3E>
escreveu:
Hi @tp3, we now know what happened in our unit tests so I thought I
would
report back.
We have our own OpenSCAD dictionary library inside the OpenFlexure
Micrsocope project, and we test it really carefully because I am
worried
about edge cases causing things to fail. We also always have
hardwarnings
on, so it must run without warnings.
We use the C-style for loop list comprehensions quite a bit, iterating
more than one value in the last section. An dummy example of some code
that
generates the warnings we were getting is:
b= [1,2,3];
a = [for (i=-1, j=0; i<len(b); i=i+1, j=j+b[i]) j];
echo(a);
Here on the last iteration i becomes equal to b, so the loop will
exit.
But the next value of j is calculated before the loop exits. This
means
that OpenSCAD 2021 throws a the warning:
WARNING: undefined operation (number + undefined)
We have just adjusted our library so we no longer set off this
warning.
Our resulting code is actually nicer.
I am not sure if I would class this as unexpected behaviour from
OpenSCAD.
Warning about undef in arithmetic is so important, but then it does
make
it
slightly harder to iterate over all values in an array. But perhaps
there
is a nicer way that I am missing.
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On 25.04.21 13:50, julianstirling wrote:
I am not sure if I would class this as unexpected behaviour from
OpenSCAD. Warning about undef in arithmetic is so important, but
then it does make it slightly harder to iterate over all values
in an array. But perhaps there is a nicer way that I am missing.
No, as Ronaldo already mentioned, it's more an issue with the
implementation of the c-style loop. As the discussion in the
linked issue indicates it might be possible to fix without
bad side effect, specifically as this extra evaluation is not
supposed to have meaningful side effects (it could have an
echo() embedded, but skipping that seems ok too).
As you have a bigger project with a nice CI setup, it would be
great to set that up as reference for the nightly builds of
OpenSCAD. There's a couple of sorely needed but still slightly
tricky changes in progress that will help fixing some of the
strange corner cases of OpenSCAD. Having a couple of reference
projects could help catching potential issues in a more
automated way early and not only after a full release.
Do you think that makes sense? I would not ask much of your time,
maybe just a question here and there when setting things up.
I'm not sure when I'll have the time to get that going, but I
believe it might be quite useful.
ciao,
Torsten.