combined_hash

#include <functional>

/** Combine hash in seed with hash of t1 */
template <typename T1>
void hash_combine(size_t& seed, const T1& t1)
{
    // Combine hashes
    seed ^= std::hash<T1>()(t1) + 0x9e3779b9 + (seed << 6) + (seed >> 2);
}

/** Combine hash in seed with hashes in t1, t2, args... */
template <typename T1, typename T2, typename... Ts>
void hash_combine(size_t& seed, const T1& t1, const T2& t2, const Ts&... args)
{
    // Process t1 and then the rest of the argument pack
    hash_combine(seed, t1);
    hash_combine(seed, t2, args...);
}

/** Calculate a combined hash from args */
template <typename... Args>
size_t& combined_hash(const Args&... args)
{
    size_t hash = 0;

    hash_combine(hash, args...);

    return hash;
}