I think that you may have made a bad choice of string value for $foo in that some other posters think that you want to interpolate the value of $bar. Is it the case that you want two distinct and possibly unrelated values for $foo, one a string and the other an array reference? If so, I would suggest that you might have a design flaw somewhere (which a hash solution might fix), but on the off chance that you really need this, you could use overload -- though I wouldn't recommend it.

#!/usr/local/bin/perl -w
use strict;
                                                                      
+          
package ArrayOrString;
use overload
    '""'  => \&to_string;
                                                                      
+          
my $STRING_VAL = '';
                                                                      
+          
sub new {
    my ($class, $arrayref) = @_;
    die "not an array ref" unless 'ARRAY' eq ref $arrayref;
    bless $arrayref, $class;
}
                                                                      
+          
sub string {
    shift;
    $STRING_VAL = shift if @_;
    return $STRING_VAL;
}
                                                                      
+          
sub to_string {
    return $STRING_VAL;
}
                                                                      
+          
package main;
                                                                      
+          
my @bar = qw(one two three);
my $foo = ArrayOrString->new(\@bar);
$foo->string('bar');
print "*** $foo ***\n";
                                                                      
+          
foreach my $baz (@$foo) {
    print "Val: $baz \n";
}
[download]

Update: Whoops! I see your reply to dragonchild. You want soft references and that's a bad idea. Ignore my neat code, it doesn't do what you want, though it does what I said it does :)