Hello fellow monks. This is actually the first time I end up posting here, because until now, I always found my answer while writing my question, or just before clicking "create". You were all my rubber ducks :). But I can't understand this one.

On the version of perl I have here (strawberry v5.20), this code yields two warnings:

use strict;
use warnings;

use List::Util qw( min );

use Data::Dump qw( pp );

my (@_x, @_y);
my @one = 1;
my @two = 0.5;

pp { one => $#one, two => $#two };
pp @one, @two;
 
for my $_in (1..5) 
{ 
  push @_x, "$_in";
  my $_out = 0;
  
  #pp "$#_x", "$#one", min $#_x, $#one;
  #pp "$#_y", "$#two", min $#_y, $#two;
  
  my $x_max = min $#_x, $#one;
  my $y_max = min $#_y, $#two;
  
  pp { x => $x_max, y => $y_max };
  
  $_out += $one[$_] for 0..$x_max;
  $_out -= $two[$_] for 0..$y_max;
  
  push @_y, $_out;
}

pp { one => $#one, two => $#two };
pp @_y;
[download]

Use of uninitialized value in addition (+) at test.pl line 28
Use of uninitialized value in subtraction (-) at test.pl line 29

Unless I'm mistaken, this means I'm reaching for elements outside of @one and @two, even though $x_max and $y_max should not exceed the highest index.

I don't understand how with $#one == 0 and $x_max = min $#_x, $#one I find that $x_max > 0. What surprises me even more is that the warning disappears when I add the two commented lines (removing the quotes shows that min returns an alias and not a copy of the value).

Did I miss something obvious, or is this some weird side effect of my code?