#!/usr/bin/perl
use strict;
use warnings;
use Data::Dump qw(pp);
$| =1;  #some advanced stuff to make the printout in the right order
        #forget about this for now...

# a reference to an array is a scalar value..

my $ref2_array_first_run  = return_array(1);
my $ref2_array_second_run = return_array(4);

print "Scalar value of \$ref2_array_first_run is $ref2_array_first_run\n";
pp $ref2_array_first_run;

print "Scalar value of \$ref2_array_second_run is $ref2_array_second_run\n";
pp $ref2_array_second_run;

my @copy = @$ref2_array_first_run;  # copy array to another block of
                                    # memory called @copy
$ref2_array_first_run = undef;      # zap memory that first call to
                                    # return_array() allocated.
pp $ref2_array_first_run;           # memory no long in use!

pp \@copy;                          # A copy of the first run now
                                    # exists in other memory


sub return_array 
{
    my $start_num = shift; #so that each run is different
    
    # my @array = (1, 2, 3);
    my @array = ($start_num..$start_num+2);
    
    # Question is whether or not calculate() should modify @array?
    # If so, here are 2 ways to do that...
    
    foreach my $element (@array) {
    
        # calculate($element); # does not modify @array!
        # these 2 calculate methods both modify @array...
        
        $element = calculate($element); # most obvious way
        calculate2 (\$element);         # using ref to $element
    }
    return \@array;
}

sub calculate
{
   my $value = shift;
   return ($value *5);  #multiplies by 5 
}

sub calculate2
{
   my $ref2scalar = shift;
   $$ref2scalar *= 10;  # multiplies by 10 
                        # no "return value" needed
}
__END__
Prints:
## This shows that the ARRAY references created by run1 and run2
## do indeed point to different memory

Scalar value of $ref2_array_first_run is ARRAY(0x6c35e0)
[50, 100, 150]  # "pretty print" output for 1,2,3
Scalar value of $ref2_array_second_run is ARRAY(0xfcb430)
[200, 250, 300] #  "pretty_print" output for 4,5,6
undef           # memory used for the first array creation is GONE.
[50, 100, 150]  # the @copy of the first run still exists