use strict;
use warnings;
{
    package foo;
    sub new { bless {}, shift};
}
my $foo = foo->new();
print "ref(foo) = ",ref($foo), "\n";
print "foo is a hash\n" if UNIVERSAL::isa($foo,'HASH');


my $bar = {a => 1};
# The following won't work 
# print "bar is a hash\n" if $bar->isa('HASH');

print "bar is a hash\n" if UNIVERSAL::isa($bar,'HASH');