Because 'seek' is a perl function that magically accesses my own SEEK subroutine, but which *always* coerces its second argument (the first is the fh) to an integer! Do you doubt this? See the code below!
(btw: I fixed my little problem by multiplying the times in the argument list by 1000 and then dividing by same within SEEK.)
- GRR
#!/usr/bin/perl
use strict;
package myNull;
sub TIEHANDLE {
my $class = shift;
my $fh = local *FH;
bless \$fh, $class;
}
sub SEEK {
my $class = shift;
my $offset = shift;
my $whence = shift;
print "SEEK: offset = $offset\n";
}
1;
perl -e 'use myNull; tie *null, "myNull"; seek null, 5.5, 0;'
SEEK: offset = 5
Call with an integer offset in ms rather than a float in seconds. Problem, if not solved, worked around fairly easily. :)
sub READ {
if ( @_ == 3 ) {
# read into buffer
} else {
# read into buffer at offset
}
It turned out that even if you called read() with 3 arguments, READ was always called with 4 arguments, and the 4th (the offset) was set to zero (which I admit makes sense, but it threw a warning about uninitialized value in [substr] in this particular case, and made the conditional pointless).
Many tie methods force their arguments into more regular forms. You can't get anything but non-negative integers for indices into tied arrays ($x[-1] calls $obj->FETCH( $obj->FETCHSIZE() -1 ), for example). You can't use nor return a list where you would usually have a scalar. And so on...
An exception appears to be that you can get more than just the string value for keys passed to tied hashes (and I suspect this was not always the case).
- tye
I thought I might be able to pass a negative number to FETCH if the index was negative and bigger than the number of elements.
Turns out FETCH is not even called in that situation, even though FETCH *is* called for indexes greater than the highest existing index.
use Tie::Array qw( );
our @ISA = 'Tie::StdArray';
sub FETCH {
my ($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
Perl 5.6.1 & 5.8.6