Once again, you have correctly corrected me. :-) Thanks. I didn't happen to notice that OP was passing a reference, so, as you say, the issue was moot. On the other hand, whilst you are right that Perl passes by reference and I am grateful for the correction, the usual semantics of parameter usage does involve copies that can clobber a passed in tied scalar:

In this code sample, which compares the usage of a parameter array element directly ($_[0]) with one common usage of the array ($param = shift @_) 

use strict;
use warnings;

{
  package TiedObject;

  sub TIESCALAR {
    my $sClass = shift;
    return bless([ @_ ], $sClass);
  }
  sub STORE {}
  sub FETCH { shift->[0]; }
}

my $sErr;
tie $sErr, 'TiedObject', 5, "More data";
printTiedObject($sErr);

sub printTiedObject {
  my $oErr = tied($_[0]);

  #does not copy scalar, prints out "...is tied to..."
  print "using \@_ directly\n";
  if (defined($oErr)) {
    print "\$_[0] is tied to <$oErr>\n";
  } else {
    print "\$_[0] is not tied";
  }

  #copies scalar, prints out "..is not tied"
  print "\nafter \$param0 = shift \@_\n";
  my $param0 = shift @_;
  $oErr = tied ($param0);
  if (defined($oErr)) {
    print "\$param0 is tied to <$oErr>\n";
  } else {
    print "\$param0 is not tied\n";
  }
}

[download]

we get the following output

using @_ directly
$_[0] is tied to <TiedObject=ARRAY(0x814ed48)>

after $param0 = shift @_
$param0 is not tied

[download]

Best, beth

In reply to Re^3: Using a tied scalar as an in memory file by ELISHEVA
in thread Using a tied scalar as an in memory file by duncs

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