I am not sure if the title is appropriate, but here is my problem -- given the following code

# In my script
my $dbh = DBI->connect();
my $id  = 1;
my $obj = Obj->new($dbh, $id);
my $foo = $obj->foo;
my $bar = $obj->bar;

# In a nearby package
package Obj;

use constant PI => 3.14;
use constant  G => 9.81;

my %foo_cache;
my %bar_cache;

sub new {
  my ($class, $dbh, $id) = @_;

  my $self = bless {}, $class;
  $self->{dbh} = $dbh;
  $self->{id} = $id;
  
  return $self;
}

sub dbh {
  my $self = shift;
  return $self->{dbh};
}

sub id {
  my $self = shift;
  return $self->{id};
}

sub foo {
  my $self = shift;
  my $id   = $self->id;
  my $dbh  = $self->dbh;

  unless ($self->{foo}) {
  
    # check if foo is in cache
    if (exists $foo_cache{$id}) {
      # return from cache
      $self->{foo} = $foo_cache{$id};
    }
    else {
      $foo_cache{$id} = PI * query_foo_from_db_using($dbh, $id);
      $self->{foo} = $foo_cache{$id};
    }
  }
  
  return $self->{foo};
}

sub bar {
  my $self = shift;
  my $id   = $self->id;
  my $dbh  = $self->dbh;

  unless ($self->{bar}) {
    # check if bar is in cache
    if (exists $bar_cache{$id}) {
      # return from cache
      $self->{bar} = $bar_cache{$id};
    }
    else {
      $bar_cache{$id} = G * query_bar_from_db_using($dbh, $id);
      $self->{bar} = $bar_cache{$id};
    }
  }
  
  return $self->{bar};
}

1;
[download]

I want to convert the package code above to something like

package Obj;

use constant PI => 3.14;
use constant  G => 9.81;

my %foo_cache;
my %bar_cache;

use parent ('Obj::Foo', 'Obj::Bar');

sub new {
  my ($class, $dbh, $id) = @_;

  my $self = bless {}, $class;
  $self->{dbh} = $dbh;
  $self->{id} = $id;
  
  return $self;
}

sub dbh {
  my $self = shift;
  return $self->{dbh};
}

sub id {
  my $self = shift;
  return $self->{id};
}

1;

###############
package Obj::Foo;

sub foo {
  my $self = shift;
  my $id   = $self->id;
  my $dbh  = $self->dbh;

  unless ($self->{foo}) {
  
    # check if foo is in cache
    if (exists $Obj::foo_cache{$id}) {
      # return from cache
      $self->{foo} = $Obj::foo_cache{$id};
    }
    else {
      $Obj::foo_cache{$id} = Obj::PI * query_foo_from_db_using($dbh, $
+id);
      $self->{foo} = $Obj::foo_cache{$id};
    }
  }
  
  return $self->{foo};
}

1;
[download]

Update: The following line $self->{foo} = $Obj::foo_cache{$id}; above doesn't seem to work. How do I access a class variable from Obj.pm from within Obj::Foo.pm? Or, what is a better way to accomplish what I am trying to do?

###############
package Obj::Bar;

sub bar {
  my $self = shift;
  my $id   = $self->id;
  my $dbh  = $self->dbh;

  unless ($self->{bar}) {
    # check if bar is in cache
    if (exists $Obj::bar_cache{$id}) {
      # return from cache
      $self->{bar} = $Obj::bar_cache{$id};
    }
    else {
      $Obj::bar_cache{$id} = Obj::G * query_bar_from_db_using($dbh, $i
+d);
      $self->{bar} = $Obj::bar_cache{$id};
    }
  }
  
  return $self->{bar};
}

1;
[download]

Besides the fact that making Obj inherit from Foo and Bar doesn't seem right (after all, Obj is not a type of Foo or Bar; instead, Foo and Bar are parts of Obj) it does work. My question to you before I embark on the above design -- anything wrong with this? Do I have to be aware of any gotchas?

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