Indeed; the extra referencing is being added by the \&buildlist($_), which is an unnecessary complication. There's no need to build a reference here at all, since buildlist() already explicitly returns one, and it's arguably confusing because \& is normally used to take a reference to a subroutine, not to a return value.

Removing the \& there would enable all the ${$$...}-type constructions to be simplified, so for example the assignment to @tmp would then become just @{$ref->[3]}. This is probably a Good Thing.

"Extra-referencing?!!" I was thinking the \& and the \@ matched, wrt the "type" of the return value. So you've given me something to think about -- I'll try and apply this. Thanks much! ps. the exercise is 5-2. I like the book, it's well structured ;)

use O qw' Deparse -p ';
print \&reference; # real ref
print \&call(1);  # ref to return value
print \( &call(1) ); # same as above, ref to return
print \( call(1) ); # same as above, ref to return
__END__
print((\&reference));
print(\(&call(1)));
print(\(&call(1)));
print(\(call(1)));
__DATA__
[download]

#!/usr/bin/perl -w
use strict;

my %all;

open(INPUT,"<coconet.dat") || die "Can't open coconet.dat";
while (<INPUT>) {
    if ($_ =~ /^#/) { next }
    my ($src, $dest, $bytes) = split;
    # hash of hashes holds the from->to transmission TOTALS; we do not
+ keep all the data
    $all{$src}{$dest}+=$bytes;    
}
close(INPUT);

# simple use of map to create array of references to hashes: my @refli
+st = map { \%{$all{$_}} } keys %all;
# so...create an array of references to arrays (from map callback) of 
+scalars and REFS TO existing hashes and new anonymous arrays! 
my @reflist = sort { $$b[2] <=> $$a[2] } map buildlist($_), keys %all;
+  
# sort by the total of TOTALS 

foreach my $ref (@reflist) { 
    print "$$ref[0] $$ref[2]\n";
    # the next two are the same:
     foreach my $line (@{$ref->[3]}) { print "\t$line ${$ref->[1]}{$li
+ne}\n" }
    # foreach my $line (@{$$ref[3]}) { print "\t$line ${$$ref[1]}{$lin
+e}\n" }
}

sub buildlist {
    my $site = $_;
    my @tmp;
    $tmp[0]=$site;
    $tmp[1]=\%{$all{$site}};
    foreach (keys %{$tmp[1]}) { $tmp[2]+=${$tmp[1]}{$_} }
    # make element 3 a reference to an anonymous array of scalars (the
+ dest site names, ranked)
    @{$tmp[3]} = sort { ${$tmp[1]}{$b} <=> ${$tmp[1]}{$a} } keys %{$tm
+p[1]};
    return \@tmp;   # 0=site name, 1=hash ref, 2=total bytes for all t
+ransmissions from site, 3=ranked dest names ref
}

__DATA__
2000 lines, eg:
gilligan.crew.hut lovey.howell.hut 4721
thurston.howell.hut lovey.howell.hut 4046
professor.hut ginger.girl.hut 5768
gilligan.crew.hut laser3.copyroom.hut 9352
gilligan.crew.hut maryann.girl.hut 1180
fileserver.copyroom.hut thurston.howell.hut 2548
skipper.crew.hut gilligan.crew.hut 1259
[download]

# the next THREE are the same:
# foreach my $line (@{$ref->[3]}) { print "\t$line ${$ref->[1]}{$line}
+\n" }
# foreach my $line (@{$$ref[3]}) { print "\t$line ${$$ref[1]}{$line}\n
+" }
foreach my $line (@{$$ref[3]}) { print "\t$line $all{$$ref[0]}{$line}\
+n" }
}
[download]

Notes ;)