sub AUTOLOAD {
    return if $AUTOLOAD eq __PACKAGE__.'::'.'DESTROY';
    my $self = shift;
    (my $func = $AUTOLOAD) =~ s/.*:://;
    if ($self->{extension}) {
        my $method = join '::', __PACKAGE__, $self->{extension}, $func;
        $method->($self,@_);
    }
    else {
        die "method $func not defined for $self\n";
    };
}