hash.h

#ifndef CACHEMERE_HASH_H
#define CACHEMERE_HASH_H
 
#include <cstdint>
 
namespace cachemere {
 
template<typename Key, typename KeyHash, typename... Tail> struct MultiHash;
 
// Base case.
template<typename Key, typename KeyHash> struct MultiHash<Key, KeyHash> {
    // Declare this type as transparent - this is needed for abseil maps to support heterogeneous lookup.
    using is_transparent = void;
 
    size_t operator()(const Key& key) const
    {
        return m_hash(key);
    }
 
private:
    KeyHash m_hash;
};
 
// Recursive case.
template<typename Key, typename KeyHash, typename... Tail> struct MultiHash : public MultiHash<Key, KeyHash>, public MultiHash<Tail...> {
    // Declare this type as transparent - this is needed for abseil maps to support heterogeneous lookup.
    using is_transparent = void;
 
    // Need to bring back operator() declarations from parent types, so they can all be considered as overloads.
    using MultiHash<Key, KeyHash>::operator();
    using MultiHash<Tail...>::     operator();
};
 
}  // namespace cachemere
 
#endif  // CACHEMERE_HASH_H