sub mem {
    print "$_[0]:\n";
    system "/bin/ps", "-osize,vsize", $$;
}

my @a;
my %tests = (
    # immediate data - no references
    iter_flat =>    
        sub {
            my $n = shift;
            push @a, $_*42 for 1..$n;
        },
    func_flat =>
        sub {
            my $n = shift;
            @a = map $_*42, 1..$n;
        },

    # indirect/referenced data
    iter_ref =>
        sub {
            my $n = shift;
            push @a, [ $_*42 ] for 1..$n;
        },
    func_ref =>
        sub {
            my $n = shift;
            @a = map [ $_*42 ], 1..$n;
        }
);

my $what = shift @ARGV;
my $n    = shift @ARGV || 10_000_000;

mem("before");
$tests{$what}->($n);
mem("after");

##</code><code>##

$ ./883539.pl iter_flat         
before:
   SZ    VSZ
  608  22032
after:
   SZ    VSZ
395196 416620

$ ./883539.pl func_flat
before:
   SZ    VSZ
  608  22032
after:
   SZ    VSZ
1390892 1412316           #  map needs 3.5 times as much


$ ./883539.pl iter_ref 
before:
   SZ    VSZ
  608  22032
after:
   SZ    VSZ
1547832 1569256

$ ./883539.pl func_ref
before:
   SZ    VSZ
  608  22032
after:
   SZ    VSZ
2571632 2593056           #  map needs 1.7 times as much