# Computation of Relationships between Two Lists in List::Compare's Regular Mode
# Regular Mode => Compares only two lists; computes all relationships at once;
# stores the results in a hash which is blessed into the List::Compare object.
# Below:  _init(), which is called by List::Compare's constructor and which returns
# a reference to the hash which the constructor will bless.

sub _init {
    my $self = shift;
    my ($unsortflag, $refL, $refR) = @_;
    my (%data, %seenL, %seenR);
    my @bag = $unsortflag ? (@$refL, @$refR) : sort(@$refL, @$refR);

    my (%intersection, %union, %Lonly, %Ronly, %LorRonly);
    my $LsubsetR_status = my $RsubsetL_status = 1;
    my $LequivalentR_status = 0;

    foreach (@$refL) { $seenL{$_}++ } 
    foreach (@$refR) { $seenR{$_}++ } 

    foreach (keys %seenL) {
        $union{$_}++;
        if (exists $seenR{$_}) {
            $intersection{$_}++;
        } else {
            $Lonly{$_}++;
        }
    }
    
    foreach (keys %seenR) {
        $union{$_}++;
        $Ronly{$_}++ unless (exists $intersection{$_});
    }

    $LorRonly{$_}++ foreach ( (keys %Lonly), (keys %Ronly) );

    $LequivalentR_status = 1 if ( (keys %LorRonly) == 0);

    foreach (@$refL) {
        if (! exists $seenR{$_}) {
            $LsubsetR_status = 0;
            last;
        }
    }
    foreach (@$refR) {
        if (! exists $seenL{$_}) {
            $RsubsetL_status = 0;
            last;
        }
    }
    
    $data{'seenL'}                = \%seenL; 
    $data{'seenR'}                = \%seenR; 
    $data{'intersection'}         = $unsortflag ? [      keys %intersection ] 
                                                : [ sort keys %intersection ];
    $data{'union'}                = $unsortflag ? [      keys %union ]
                                                : [ sort keys %union ];
    $data{'unique'}               = $unsortflag ? [      keys %Lonly ] 
                                                : [ sort keys %Lonly ];
    $data{'complement'}           = $unsortflag ? [      keys %Ronly ] 
                                                : [ sort keys %Ronly ];
    $data{'symmetric_difference'} = $unsortflag ? [      keys %LorRonly ] 
                                                : [ sort keys %LorRonly ];
    $data{'LsubsetR_status'}      = $LsubsetR_status;
    $data{'RsubsetL_status'}      = $RsubsetL_status;
    $data{'LequivalentR_status'}  = $LequivalentR_status;
    $data{'bag'}                  = \@bag;
    return \%data;
}