Does Perl Always Pass Argument By Reference?

[Akino877]

Hello,

I read on one web page that Perl always passes its arguments by reference.
But on another web page, it was said that Perl can pass its argument by
value :

   printHash(%hash);

Could someone please tell me if the second web page is correct?

Thank you - Akino

[Kelicula]

You need to be clearer as to where you are talking about perl passing things to. Do you mean mean passing arguments to a subroutine? A hash in perl is really an array, (not really but when it comes to passing things) if you pass a named hash to a subroutine (in certain context) it will be "flattened" into an array where the first element is the "key" and the second is the "value" and so on... as in:
%hash = ( name => 'Jim', age => '29');
will become:
(name, Jim, age, 29);
When passed...

[Kelicula]

If you pass an anonymous hash it will be treated as a reference.
eg:
$hash = { name => 'Jim', age => '29'};

[Akino877]

Hi Kelicula,

Thank you very much for your reply.

Akino

[Kelicula]

When passing to subroutines, the convention is; if there are more than 3-4 things you are passing you should probably be using an anonymous hash, otherwise you can just pass the value directly.
eg:

sub passing_things {
    my $thing = shift;
    do stuff with thing passed...
}
# Then later...
passing_things($variable);

The value in $variable will be passed to the subroutine.
However if you find you are sending a lot of things you can just use an anonymous hash:

sub passing_more_things {
    my $things = shift;
    do many things with lots of stuff...
}
# then later...
passing_more_things({ one => $var, two => $var2, three => $var3, four => $var4});

# If you want to you can pass different kinds of things explicitly:
passing_more_things($variable, { one => $var, two => $var2}, @array);

In that case all that stuff will be "flattened" into an anonymous array "@_" inside the sub:

sub big_passing {
    my @all_the_stuff = @_;
}
# Then later
my $var = 'hello';
my @array = ('perl', 'is', 'very', 'flexible');

big_passing($var, @array, { kelicula => 'loves', all => 'things_perl'});

the contents of @all_the_stuff would be:
hello, perl, is, very, flexible, kelicula, loves, all, things_perl.

Get it?

[Akino877]

Yes, I understand it now. Thank you.