use constant CONST => {
                         foo => 'bar',
                         fiz => 'baz'
                     };

foreach (keys CONST)
{
    print "$_\n";
}

##</code><code>##

Type of arg 1 to keys must be hash (not constant item)

##</code><code>##

foreach (keys %{CONST})
{
    print "$_\n";
}

##</code><code>##

Variable "%CONST" is not imported