#!/usr/bin/perl

use strict;
use warnings;

package Foo;

sub new
{
 my $class=shift;
 my $self={};
 $self->{count}=0;
 bless($self,$class);
 return $self;
}

sub counter
{
 my $self=shift;
 if(@_)
 {
  my $opt=shift;
  my $val=@_?shift(@_):undef;
  return 0 unless($opt=~/^[+-=]{1,2}|^\d+$/ );
  if($opt eq '=')
  {
   return 0 unless(defined($val));
   $self->{count}=$val+0;
  }
  elsif($opt eq '+=')
  {
   return 0 unless(defined($val));
   $self->{count}+=$val;
  }
  elsif($opt eq '-=')
  {
   return 0 unless(defined($val));
   $self->{count}-=$val;
  }
  elsif($opt eq '++')
  { $self->{count}++; }
  elsif($opt eq '--')
  { $self->{count}--; }
  elsif($opt=~/^\d+$/)
  { $self->{count}=$opt; }
  else
  { return 0; }
  return 1;
 }
 else
 { return $self->{count}; }
}

package main;

my $val=Foo->new();

$val->counter( 3 );
print $val->counter."\n";

$val->counter('++');
print $val->counter."\n";

$val->counter('--');
print $val->counter."\n";

$val->counter qw( =  10);
print $val->counter."\n";

$val->counter qw( +=  5 );
print $val->counter."\n";

$val->counter qw( -=  20 );
print $val->counter."\n";