r/perl

[removed]

+= behaves differently after Data::Dump::pp. Is this a bug in Data::Dump or possibly in Perl core?

I encountered some unexpected behavior in a simple snippet where regex captures are assigned to variables, formatted via Data::Dump::pp, concatenated, and then incremented using +=.

use v5.10;
use Data::Dump qw( pp );

"9." =~ /^ (\d+) \. (\d*) $/x;
my $n = { i => $1, f => $2 };

say "pp output: ", pp $n;       # { f => "", i => 9 }

$n->{f} = "$n->{i}$n->{f}";     # "9"
$n->{f} += 2;                   # expected: 11

say "result: $n->{f} (expected: 11)";

Observed output:

pp output: { f => "", i => 9 }
result: 2 (expected: 11)

Instead of evaluating 9 + 2 = 11, the += 2 operation behaves as if the value of $n->{f} were numerically 0, resulting in 2.

I am not looking for a 'workaround' (I have already avoided it in the production code), but I would like to understand what causes this, and whether it warrants a bug report to Data::Dump or Perl core.

Observations

I tested several variations:

• using scalar variables instead of hash elements,
• using a direct assignment of constants instead of assigning the regex variables,
• removing the pp output.

The behavior changes as follows:

• With pp $n removed, the result is always correct.
• With scalar variables instead of hash elements, calling pp always causes the wrong value, regardless of whether the value originated from regex captures or constants.
• With hash elements, calling pp does not affect the result after constant assignment, but it does after assignment from regex captures.

My suspicion is that inspecting the variables inside Data::Dump::pp somehow alters their internal state, causing the numeric operation to behave differently.

Does this look like something that should be reported to Perl core, or to the Data::Dump maintainers?

Perl version breakdown

I ran a test script using several Perl versions that I have installed using perlbrew (all with Data::Dump version 1.25):

Perl v5.10.1 – v5.26.3: The bug does not occur.

Perl v5.28.3 – v5.44.0: The bug occurs.

Reproducing the bug

I have uploaded the full test matrix script here: failing_increment.pl, together with a Bash script test_with_available_perls that runs the test script for all Perls that are installed locally with perlbrew.

Thank you for your help!

Hi, On the one hand: I can't seem to find this. On the other hand, it seems so obvious to me that it must have been written before.

I'm looking for a (Newtonian) physics library, to support a (2D) game. Something where you simple define an array of objects (position, travel, mass, spin, shape, etc), and then step through time with them - as they attract each other, bounce off of each other and/or fly off into infinity. There should probably be a few global things to set: a gravity constant, the amount of dimensions required, whether or not there is friction from the environment...

Does this exist?

Hi,

I am trying to figure out how to get this sundial.pl file to create a pdf. Would anyone be able to help?

I download the zip files from here: https://sourceforge.net/projects/analemmatic/

But every time I try to run the sundial.pl file no pdf gets generated.

I have never used Perl before, so I'm not sure what to do.

I run 2 websites. Both contain a calendar with results. The calendar has buttons for previous and next months. On one website the calendar behaves as expected. On the other site the calendar stays on the current month and does not return an error.

They seemed to have got it to work reliably for a while, but for the last week I don't think I've been able to access it.

Does anybody know any news?