I go one step further than "fly weight objects". I take a lexical hash for each attribute, and index those with the object. This means you never have to use string literals to access attributes (and hence you get the full benefit of using strict), and you only need one hash query instead of two to access the attribute.

Here's my implementation of the BaseballPlayer::Pitcher class. It's totally independent of the implementation of the BaseballPlayer class (although it could be that you want to mask the constructor - but that's ok because the constructor is part of the API). I call this technique "Inside Out Objects" (people who saw my presentation at YAPC know all about it).

package BaseballPlayer::Pitcher; {
    use vars '@ISA';
    @ISA = 'BaseballPlayer';
 
    my (%ERA, %Strikeouts);
 
    sub ERA        : lvalue {$ERA        {+shift}}
    sub Strikeouts : lvalue {$Strikeouts {+shift}}
    sub DESTROY {
        my $self = shift;
        delete $ERA {$self}, $Strikeouts {$self}
    }
}
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Abigail