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