PairHash.h

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#pragma once
 
#ifndef _PAIR_HASH_H_
#define _PAIR_HASH_H_
 
namespace Utils
{
 
// or simply use boost::hash
template <typename T1, typename T2 = T1> class PairHash
{
  public:
    size_t operator()(const std::pair<T1, T2> &p) const
    {
        const auto h1 = std::hash<T1>{}(p.first);
        const auto h2 = std::hash<T2>{}(p.second);
 
        // alternative with boost combine:
        /*
        std::size_t seed = 0;
        boost::hash_combine(seed, h1);
        boost::hash_combine(seed, h1);
 
        return seed;
        */
 
        return (h1 << 5) ^ h2;
    }
};
 
} // namespace Utils
 
#endif