Here is an easy one - pass two (or more) arrays (or hashes) to a subroutine: 
use strict;

my @a = (0..4);
my @b = ('a'..'e');

&foo(@a,@b);
&bar(\@a,\@b);

sub foo {
 my (@a,@b) = @_;
 print "a: ", join(',',@a), "\n";
 print "b: ", join(',',@b), "\n";
}

sub bar {
 my ($a,$b) = @_;
 print "a: ", join(',',@$a), "\n";
 print "b: ", join(',',@$b), "\n";
}

[download]
Subroutine foo() tries to pass two arrays, and as a result they are 'squashed' into one array. Subroutine bar() passes the two arrays by reference, and because it 'asks' for references in this line: 
my ($a,$b) = @_;

[download]
the arrays are not squashed. Maybe it would be clearer if you understand that @_ is an array itself, from perldata (with a paraphrase by me): 
  You can actually put an array or hash anywhere in the
  list [subroutine arguments which are passed to @_],
  but the first one in the list will soak up all the
  values, and anything after it will become undefined.

[download]
Hence, in subroutine foo(), @a soaks up all of the elements that were meant for @b.

jeffa

L-LL-L--L-LL-L--L-LL-L--
-R--R-RR-R--R-RR-R--R-RR
F--F--F--F--F--F--F--F--
(the triplet paradiddle)

In reply to (jeffa) Re: Trying to learn about References by jeffa
in thread Trying to learn about References by dru145

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