Keeping track of a variable

Hi All,

Can someone please tell me how do we keep track of a
variable. ie Whenever a particular variable is
accessed (printed, incremented .... etc.), a counter
should increase, so that we can know how many times it
has been accesssed.

Thanks in Advance,
Regards,
Alok



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Alok Bhatt wrote:
> Hi All,
>
>  Can someone please tell me how do we keep track of a
> variable. ie Whenever a particular variable is
> accessed (printed, incremented .... etc.), a counter
> should increase, so that we can know how many times it
> has been accesssed.

The mechanism is tie, see `perldoc tie`

Here is an example: (See CPAN for others)

#!/usr/bin/perl

package Traced::Var;

use strict;

require Tie::Scalar;

our @ISA = qw(Tie::StdScalar);

sub FETCH {
my $self = shift;
print "FETCH: value is " . ${$self} . "\n";
return ${$self};
}

sub STORE {
my $self = shift;
my $val  = shift;
print "STORE: old value is " . ${$self} . "\n";
${$self} = $val;
print "STORE: new value is " . ${$self} . "\n";
return ${$self};
}

package main;

my $var;
tie $var, 'Traced::Var';

$var = 42;
print "$var\n";

$var = "The answer";
print "$var\n";

__END__