Re: lvalue trickery

Looking at the FETCH subroutine of Tie::IxHash solves the problem:

sub FETCH {
  my($s, $k) = (shift, shift);
  return exists( $s->[0]{$k} ) ? $s->[2][ $s->[0]{$k} ] : undef;  
}
[download]

You haven't stored anything in the hash yet, so $_[0]->{val}->{one} returns undef, which isn't an lvalue.

Suggested and untested solution: $h {one} = undef after the tie.

Abigail

Comment on Re: lvalue trickery Select or Download Code

Replies are listed 'Best First'.
Re: Re: lvalue trickery by broquaint (Abbot) on Jul 26, 2002 at 14:46 UTC
You haven't stored anything in the hash yet, so $_[0]->{val}->{one} returns undef, which isn't an lvalue. Erm ... `{ package foo; use Tie::IxHash; tie(my %h, 'Tie::IxHash', qw(one two three four)); sub new { bless { val => \%h } } sub val : lvalue { $_[0]->{val}->{one} } } use Data::Dumper; my $obj = foo->new; print Dumper( $obj ); __output__ $VAR1 = bless( { 'val' => { 'one' => 'two', 'three' => 'four' } }, 'foo' );` [download] I figured that the issue might be in the `FETCH` method of `Tie::IxHash`, but I thought that `tie`d variables were meant to behave just like normal variables (in terms of interface at least), apparently not. `_________ broquaint`	[reply] [d/l]

Replies are listed 'Best First'.

Re: Re: lvalue trickery
by broquaint (Abbot) on Jul 26, 2002 at 14:46 UTC

You haven't stored anything in the hash yet, so $_[0]->{val}->{one} returns undef, which isn't an lvalue.

{
    package foo;
    use Tie::IxHash;
    tie(my %h, 'Tie::IxHash', qw(one two three four));

    sub new { bless { val => \%h } }
    sub val : lvalue  { $_[0]->{val}->{one} }
}
use Data::Dumper;
my $obj =  foo->new;
print Dumper( $obj );

__output__

$VAR1 = bless( {
                 'val' => {
                            'one' => 'two',
                            'three' => 'four'
                          }
               }, 'foo' );
[download]

FETCH

Tie::IxHash

tie

_________ broquaint

[reply]
[d/l]