# Abstract class for consideration
#   name() and doit() are a base class object methods.
#   table_name() is a pure virtual method.
#   database() is a base class "static" method.

package Foo;

require Exporter;
use vars ( @ISA );
@ISA = qw( Exporter );

# this is the list of pure virtual functions which must be 
# implemented in any subclass that uses this base class.
my @VIRTUAL_METHODS = qw( table_name );

# this is the constructor, that validates the list of virtual methods.
sub new()
{
   my $class = shift @_;
   $class = ref $class if ref $class;
   my @args = @_;

   # verify pure virtual methods
   for my $method ( @VIRTUAL_METHODS )
   {
      unless ( $class->can( $method ) )
      {
         die "$class:  missing virtual method '$method'\n";
      }
   }

   # create object
   my $obj = {};
   $obj->{NAME} = shift @args;
   bless $obj, $class;

   return( $obj );
} # new

# This is a base-class function that uses a base-class data member.
# You have to call it from a specific object instance of a
# derived class.
sub name
{
   my $obj = shift @_;
   my $key = 'NAME';

   if ( scalar @_ )
   {
      $obj->{$key} = shift @_;
   }
   
   return( $obj->{$key} );
} # name

# This is a base-class function that doesn't need a class instance to
# function properly (it's not virtual, either );
sub database_name
{
   return 'Foobase';
} # database_name

# This is a base-class function that uses a virtual method
# and also uses a base-class method.
sub doit()
{
   my $obj = shift @_;
   my @args = @_;

   # Prove that base class was called from member object
   printf "In %s\::doit() for class %s, ", __PACKAGE__, ref $obj;
   printf "my name is %s, and my table is %s\n",
          $obj->name(), $obj->table_name();

   return(1);
} # doit