sub doit {
    my( $self, $a, $b ) = @_;
    $self->_validate_self( __PACKAGE__ );
    $self->{validators}{'doit_a'}->( $a );
    $self->{validators}{'doit_b'}->( $b );
    $self->{befores}{'doit'}->( $self, $a, $b );
    my( @results ) = $self->{arounds}{'doit'}->( $self->{setters}{doit}, $self, $a, $b  );
    $self->{afters}{'doit'}->( $self, $a, $b );
    return @results;
}