You don't want a two-way hash, you want two hashes that are kept in sync:

    my( %one, %two );
    Tie::Hash::Complementary->marry( \%one, \%two );
    $one{foo} = 'bar';    # Also sets $two{bar}= 'foo'
    $two{baz} = 'bif';    # Also sets $one{bif}= 'baz'
    $two{bar} = 'oof';    # Does: $one{oof} = delete $one{foo}
    $one{oof} = 'baz';    # Dies; $two{baz} can't be both oof and bif
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Now you can go find or write Tie::Hash::Complementary.

Of course you can't have overlap between the keys with a single two-way hash. It is a single hash. You found a module that does something somewhat like what you want, but also fundamentally different than what you want.

                - tye