#!/usr/bin/perl

use strict;
use warnings;

package BaseballPlayer;

use Carp;

my %attrib;
sub BEGIN {
  %attrib = map { $_ => 1 }
    qw( RBI Batting_Average Hits Runs Stolen_Bases Games_Played );
  no strict 'refs';
  for my $n ( keys %attrib ) { *$n = sub { $_[0]->{$n} } }
}

sub new {
  my( $class, %arg ) = @_;
  exists $attrib{$_} or croak "Unknown stat: $_" for keys %arg;
  $arg{$_} ||= 0 for keys %attrib;
  bless \%arg, $class;
}

package BaseballPlayer::Pitcher;
our @ISA = 'BaseballPlayer';

{
  my %object;

  sub new {
    my( $class, %arg ) = @_;
    my %pitcher_stat = map { $_ => delete $arg{$_} || 0 } qw( ERA Strikeouts );
    my $base = BaseballPlayer->new(%arg);
    my $ret = bless $base, $class;
    $object{$ret} = \%pitcher_stat;
    $ret;
  }
  sub ERA { $object{$_[0]}{ERA} }
  sub Strikeouts { $object{$_[0]}{Strikeouts} }
  sub DESTROY { delete $object{$_[0]} }
}

package main;

my $p = BaseballPlayer::Pitcher->new( Hits => 23, ERA => 4.32 );
print $p->Hits, "\n";
print $p->ERA, "\n";