my $obj = Win32::Event2Log->new(engine => 'type');

##</code><code>##


use 'base' Win32::Event2Log::Engine;

sub new {
    my ($class, %args) = @_;
    my $self = bless {%args}, $class;

    # select_engine inherited

    return $self->select_engine($self->{engine}); 
}

##</code><code>##

use Win32::Event2Log::Reader;
use Win32::Event2Log::Wevtutil;

sub select_engine {
    shift; # throw away Event2Log object, unless needed/wanted

    my ($engine) = @_;

    my %engines = (
        reader  => sub { return Win32::Event2Log::Reader->new(...); },
        wrapper => sub { return Win32::Event2Log::Wevtutil->new(...); },
    );

    $engines{$engine}->();
}