package esmith::AD;

sub doesUserExist
{
    return 0;           # default answer: 'No'
}

package esmith::AD::User;

use List::Util qw( any );

my @user_names;         # class variable

sub doesUserExist
{
    my ($self) = @_;    # assuming that $self is a hash reference

    return any { $_ eq $self->{Name} } @user_names;
}