Hashing with Boost Hash Library

[Randalphwa]

Migrated from the original repository
Original issue: serge-sans-paille/frozen#109
Originally reported by: @staticassert

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Is there a method to use the boost hash library as a hash function in frozen::unordered_map?

I have been using boost::hash in std::unordered_map to work with non-integral keys. Using boost::hash in frozen::unordered_map creates an error, because the pmh_table::lookup() function applies 2 parameters: key and static_cast<size_t>(first_seed_), whereas boost::hash only accepts 1 parameter. Is there a workaround for this?