libcruft-util/hash/tuple.hpp

#pragma once

#include "../hash.hpp"
#include "./mix.hpp"

#include <tuple>


namespace cruft::hash {
    /// Computes a hash for a tuple type by elementwise hashing, then variadic mixing.
    ///
    /// \tparam ElementT  The per-element hash type
    /// \tparam MixT      The mixing hash type. Must support variadic operator()
    template <
        typename ElementT,
        typename MixT = cruft::hash::mixer
    >
    class tuple {
    public:
        using is_transparent = void;

        template <typename ...ValueT>
        auto
        operator() (std::tuple<ValueT...> const &val) const
        {
            return compute (val, std::make_index_sequence<sizeof... (ValueT)> {});
        }

    private:
        template <typename ...ValueT, std::size_t ...IndexV>
        auto
        compute (std::tuple<ValueT...> const &val, std::index_sequence<IndexV...>) const
        {
            return MixT {} (
                ElementT {} (std::get<IndexV> (val))...
            );
        }
    };
}