in reply to List::MoreUtils' minmax bug?

I can kinda sorta reproduce this, but this probably isn't the same as your problem:

use warnings;
use strict;
use List::MoreUtils 'minmax';
my $envres = [ [], [], [{time=>0.002},{}] ];
my ($min, $max) = minmax(map {$_->{time}} @{$envres->[2]});
use Data::Dump 'dump';
dump $min, $max;
__END__
Use of uninitialized value in subroutine entry at - line 5.
Use of uninitialized value in subroutine entry at - line 5.
(undef, 0.002)

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I smell a bug... what version of Perl and what version of List::MoreUtils?

Also, are you feeding minmax plain scalars, or are they objects/tied vars/some other magical things? (See Devel::Peek)

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Re^2: List::MoreUtils' minmax bug?
by perlancar (Hermit) on Mar 16, 2016 at 18:02 UTC

    I'm on perl 5.22.0 and List::MoreUtils 0.413.

    Dumping $envres->[2][0]{time} with Devel::Peek reveals something:

    When there is no warning: 

    SV = PVNV(0x279ae10) at 0x25ca100
  REFCNT = 1
  FLAGS = (POK,IsCOW,pPOK)
  IV = 0
  NV = 0.00217268600128591
  PV = 0x2895f60 "0.0022"\0
  CUR = 6
  LEN = 10
  COW_REFCNT = 3

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    When there is a warning: 

    SV = PVNV(0x196bf40) at 0x170b110
  REFCNT = 1
  FLAGS = (POK,pPOK)
  IV = 0
  NV = 0.002889619519036
  PV = 0x1a6dbb0 "0.003"\0
  CUR = 5
  LEN = 10
Use of uninitialized value $max in numeric le (<=) at lib/Bencher/Form
+atter/ScaleTime.pm line 30.

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    Trying this with a few other perls: doesn't happen in 5.10.1, always seems to happen in 5.18.4, never seems to happen in 5.20.3 happens too in 5.20.3.

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      Wow, Bencher::Backend has a lot of code, it's difficult to tell where $envres comes from. Unfortunately I think you'll need to boil it down to a code snippet that reproduces the problem (which still smells like a bug).

      I did notice that in one place $envres comes from JSON. Here's an interesting one...

      use warnings;
use strict;
use List::MoreUtils 'minmax';
use JSON::MaybeXS 'decode_json';
use Data::Dump 'dump';
my $envres = decode_json(
    q# [ [], [], [{"time":"0.0022"},{"time":false}] ] # );
dump $envres;
my ($min, $max) = minmax(map {$_->{time}} @{$envres->[2]});
dump $min, $max;
__END__
[
  [],
  [],
  [
    { time => 0.0022 },
    { time => bless(do{\(my $o = 0)}, "JSON::PP::Boolean") },
  ],
]
Segmentation fault (core dumped)

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        Nope, JSON is not involved in this case. I am now able to produce a simpler test case, I'm updating my original post.
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Re^2: List::MoreUtils' minmax bug?
by Anonymous Monk on Mar 16, 2016 at 18:32 UTC

    Reproduce what bug? Where is the bug? 

    use List::MoreUtils 'minmax';
use Data::Dump 'dump';
dump minmax(0.002, undef);

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