subroutine prototypes in Perl are much discussed because generally using them is a bad idea. For a recent discussion see subroutine prototypes still bad?.

The bottom line is: don't do that. And a follow up line is: Always use strictures (use strict; use warnings;).

Instead of using prototypes consider:

use strict;
use warnings;

my $str = 'Welcome';
my @array = qw(to the world of);

serious ($str, \@array, 'Perl');


sub serious {
    my ($str, $arrayRef, $constStr) = @_;

    print join (' ', $str, @$arrayRef, $constStr), ".\n";
}
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Prints:

Welcome to the world of Perl.
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