dragonchild is right, you can do $main::a and $main::b, but that is not very portable...

Update I didn't mean portable, I meant re-usable...

here is code that works....

sub by_id {
    my $pkg = (caller())[0];
    ${"${pkg}::a"}->id <=> ${"${pkg}::b"}->id;
}
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dunno how good a way to do it that is... but it should work...

                - Ant