sub DoStuff {
    die 'Nothing to do in a void context' 
        if want( 'VOID' );

    if( want( 'LIST' ) ) {
        return map{
            # Do stuff to generate the list
        } ...;
    }

    my @array;
    alias( @array ) if want( 'ARRAY' );
    push @array, $stuff for ....;
    return \@array if want( 'ARRAY/REF' );

    # The callers array has been filled directly
    # If we were called in an array context.
    return;  
}