package FooParent;
use Carp 'croak';

sub new {
    # Return either a FooSpecial1 or FooSpecial2
    my( $class, %options )= @_;
    if( $options{ special } == 1 ) {
        return FooSpecial1->new( %options, special1_param => 'something' );
    } elsif( $options{ special } == 2 ) {
        return FooSpecial2->new( %options, other_special_param => 'something else' );
    } else {
        croak "Unknown special '$options{special}' requested";
    };
};

package FooSpecial1;

package FooSpecial2;

package main;

my $frobnitz = FooParent->new();