# AUTOLOAD is used to 
#  1) 'autoload' constants from the constant() function in ABC.xs  
# If the name is not a constant then it's parsed for 
#  2) a tie package-name::function-name, which if matched is executed

our $AUTOLOAD;  # implicit argument of AUTOLOAD

sub AUTOLOAD {

    # make the base name (without the "package::") 
    (my $constname = $AUTOLOAD) =~ s/.*:://;
    # call the constant lookup routine in ABC.xs
    my $val = constant($constname, 0);
    
    if ($!) {
    
        # the name in $AUTOLOAD is not a constant defined by XYZ::ABC

                      # sah = scalar/array/hash       
        if (my ($abcx, $sah, $function) = 
            $AUTOLOAD =~ /^XYZ::(ABCA?)::(Scalar|Array|Hash|BTree)::([A-Z]+)$/) {
            
            if ($sah eq 'BTree') {$sah = 'Hash'}
            if ($function eq uc("TIE$sah")) {
                my $self = shift;
                my $base_sah = shift; # sah = scalar/array/hash
                return bless \$base_sah, $self;
                
                     # Scalar or Array or Hash
            } elsif ($function eq 'FETCH'
                  || $function eq 'STORE'
                  || $sah ne 'Scalar' # Array or Hash
                  && $function =~ /^(DELETE|EXISTS|CLEAR)$/
                  || $sah eq 'Array'
                  && $function =~ /^(FETCHSIZE|STORESIZE|EXTEND|POP|PUSH|SHIFT|UNSHIFT|SPLICE)$/
                  || $sah eq 'Hash'
                  && $function =~ /^(FIRSTKEY|NEXTKEY|SCALAR)$/) {
                
                $function =~ s/KEY$/_KEY/;
                my $subname = lc($abcx) . '_' . lc($sah) . '_' . lc($function);
                my $base_sah_ref = shift;
                unshift @_, $$base_sah_ref; # dereference the base scalar/array/hash
                goto &$subname;

            } elsif ($function eq 'UNTIE'
                  || $function eq 'DESTROY') {
                return;  # do nothing
        }   }
        croak "$AUTOLOAD is not a defined constant or subroutine for XYZ::ABC";
    }
    # the name in $AUTOLOAD is a constant defined by XYZ::ABC: define it for perl
    eval "sub $AUTOLOAD { $val }"; # can this be $constname rather than $AUTOLOAD?
    goto &$AUTOLOAD; # can this just be 'return' if all of the defined names really are constants?
}