in reply to Interesting SEEK behavior on tied filehandle

Many tie methods force their arguments into more regular forms. You can't get anything but non-negative integers for indices into tied arrays ($x[-1] calls $obj->FETCH( $obj->FETCHSIZE() -1 ), for example). You can't use nor return a list where you would usually have a scalar. And so on...

An exception appears to be that you can get more than just the string value for keys passed to tied hashes (and I suspect this was not always the case).

- tye        

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Re^2: Interesting SEEK behavior on tied filehandle ($x[-@x-1])
by ikegami (Patriarch) on Aug 02, 2006 at 20:29 UTC

    I thought I might be able to pass a negative number to FETCH if the index was negative and bigger than the number of elements.

    Turns out FETCH is not even called in that situation, even though FETCH *is* called for indexes greater than the highest existing index. 

    use Tie::Array qw( );
our @ISA = 'Tie::StdArray';

sub FETCH {
   my ($self, $idx) = @_;
   warn("Fetching index $idx\n");
   return $self->SUPER::FETCH($idx);
}

my @a;
tie @a, __PACKAGE__;
$#a = 4;

my $s;
$s = $a[-@a+1];  # Fetching index 1
$s = $a[-@a];    # Fetching index 0
$s = $a[-@a-1];  # FETCH not called!

$s = $a[@a];     # Fetching index 5

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    Perl 5.6.1 & 5.8.6

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