#!/usr/bin/perl

use strict;

my $n = 25;
my $m = 16;

my $a = [ 0..$n-1 ];            # create list reference

sub foo  {
    my ($aref, @idx) = @_;      # unpack sub arguments
    foreach my $i ( @idx ) {
        $aref->[$i] = 42;       # dereference element using ->
    }
}

my @subarray;                   # create list
for ( my $i=0; $i < $m; $i += 2 ) {
    push @subarray, $a->[$i];   # dereference element using ->
}

foo($a, @subarray);             # pass list reference and list

print join ', ', @{ $a };       # dereference list using @{ }