How do I customize hashing and equality with std::deque?

In C++, the standard library provides various containers, including `std::deque`, which does not have built-in hashing and equality functions. However, you can customize these functionalities by creating your own hashing and equality functions. This is particularly useful when you want to use `std::deque` as a key in associative containers, such as `std::unordered_map`. Below is an example of how to achieve this:

Keywords: C++, std::deque, hashing, equality, custom hash, unordered_map

Description: Learn how to customize hashing and equality for std::deque in C++. This guide provides a clear example and explanation of creating a custom hash function for use in unordered containers.


        #include 
        #include 
        #include 
        #include 

        // Custom hash function for std::deque
        struct deque_hash {
            template 
            std::size_t operator()(const std::deque& d) const {
                std::size_t hash = 0;
                for (const auto& elem : d) {
                    hash ^= std::hash{}(elem) + 0x9e3779b9 + (hash << 6) + (hash >> 2);
                }
                return hash;
            }
        };

        // Custom equality function for std::deque
        struct deque_equal {
            template 
            bool operator()(const std::deque& lhs, const std::deque& rhs) const {
                return lhs == rhs;
            }
        };

        int main() {
            // Create an unordered_map using std::deque as key
            std::unordered_map<:deque>, std::string, deque_hash, deque_equal> myMap;

            std::deque key1 = {1, 2, 3};
            myMap[key1] = "First";

            std::deque key2 = {4, 5, 6};
            myMap[key2] = "Second";

            // Accessing the map using a std::deque key
            for (const auto& pair : myMap) {
                std::cout << "Key: {";
                for (const auto& k : pair.first) {
                    std::cout << k << " ";
                }
                std::cout << "} - Value: " << pair.second << std::endl;
            }

            return 0;
        }

Keywords: C++ std::deque hashing equality custom hash unordered_map

How do I customize hashing and equality with std::deque?

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How do I customize hashing and equality with std::deque?

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