Re: Max of 23 and 27 is 23?

[ikegami]

$#a returns a magical value in lvalue contexts. (It used to always returns a magical value, but this was optimized.)

$ perl -MDevel::Peek -e'@a=qw( a b c ); sub { Dump($_[0]) }->( $#a );'
SV = PVMG(0x1d36630) at 0x1cfcfd0
  REFCNT = 1
  FLAGS = (GMG,SMG)
  IV = 0
  NV = 0
  PV = 0
  MAGIC = 0x1cf6ab0
    MG_VIRTUAL = &PL_vtbl_arylen
    MG_TYPE = PERL_MAGIC_arylen(#)
    MG_OBJ = 0x1d07d10

The behaviour you observe is a missing SvGETMAGIC(sv) to handle such scalars.

use strict;
use warnings;

use List::Util      qw( max );
use Variable::Magic qw( cast wizard );

# Make $x a magical variable that always returns 5.
cast(my($x),
   wizard(
      get => sub { ${ $_[0] } = 5 },
   )
);

$x = 3;

if ($ARGV[0]) { no warnings 'void'; 0+$x }

print('max($x, 4)=', max($x, 4), "\n");
print('$x=', $x, "\n");

$ perl a.pl 0
max($x, 4)=4
$x=5

$ perl a.pl 1
max($x, 4)=5
$x=5

[tye]

The behaviour you observe is a missing SvGETMAGIC­(sv) to handle such scalars.

Which is pretty much to be expected with the vast majority of XS code. Which is one reason why I almost never use List::Util routines. Must use XS for "speed!". Correctness, well, that doesn't matter quite as much.

[Anonymous Monk]

> Which is one reason why I almost never use List::Util routines. Must use XS for "speed!". Correctness, well, that doesn't matter quite as much. The authors care about correctness. However, they cannot fix bugs that they are not informed of.